Flashcards in Midterm 1 Deck (221):
Geology is a complex, integrated system of related parts, components, or subsystems
What are the principle subsystems of the earth?
Explain historical geology?
Historical geology is concerned with the origin and evolution of Earth's continents, oceans, atmosphere, and life
What is a theory?
In science, a theory is NOT a hunch or guess, but a reliable explanation supported by a large amount of evidence.
e.g. plate tectonics is a theory
How is a theory derived?
from the scientific method, which involves:
–gathering and analyzing facts
–formulating hypotheses to explain the phenomenon
–testing the hypotheses
–and finally proposing a theory.
–Science makes no claim about the existence or nonexistence of the supernatural.
What is a hypothesis?
a tentative explanation
What is a scientific theory?
theory is a testable explanation for some natural phenomenon, that is supported by a large body of evidence
Outline how the universe was formed
• The “Big Bang” theory of how the universe formed is broadly accepted
• Massive explosion 13.7 Ga forms all the universe's known matter and energy
—even space and time
• Immediately after, universe expanded with incomprehensible speed from its pebble-size origin to astronomical scope
• Expansion has continued, but much more slowly, over the ensuing Ga
What is earth's place in the solar system?
–Earth condensed as a solid body from the solar nebula about 4.6 billion years ago.
–Soon after internal heat differentiated the Earth into a layered planet.
Explain how earth is a dynamic and evolving planet?
• Earth has continuously changed during its 4.6 billion year existence as a result of interactions between its various subsystems and cycles.
• Size, shape and distribution of continents and ocean basins have changed.
• Composition of the atmosphere has evolved.
What are the concentric layers of the earth?
Describe the composition of the earth's core
The core consists of:
–a small, solid inner region
–a larger, liquid outer portion
• Composed of iron and a small amount of nickel
Describe the composition of the earth's mantle
• The Mantle –Surrounds the core and is divided into:
• a solid lower mantle.
• a partially molten asthenosphere that overall behaves plastically and flows slowly.
• a solid upper mantle.
–Composed primarily of peridotite, a rock made of the mineral olivine (and it’s high density polymorphs).
Describe the composition of the earth's crust
• The Crust
•Thick Continental ≤80km
• Thin Oceanic ≤10km
–Surrounds the lower mantle.
–Behaves plastically and slowly flows.
–Partial melting in the asthenosphere generates magma (molten rock) that rises to the Earth’s surface.
• The Lithosphere
–The solid outer layer of the Earth.
–The crust and the upper most mantle.
Explain the theory of plate tectonics
The lithosphere is composed of rigid plates that diverge, converge, or move sideways past one another over the asthenosphere.
• Earthquakes and volcanoes occur at the boundaries
Explain the importance of plate tectonic theory in relation to earth systems
–Plate tectonic theory is a unifying explanation for many geologic features and events, helping us understand the composition and internal processes of Earth on a global scale.
Explain the theory of organic evolution
• that all living things are related.
• descent, with modification, from organisms living in the past.
• Charles Darwin proposed that the mechanism of natural selection results in survival to reproductive age of organisms best suited to their environment.
• Fossils, the remains of once-living organisms, provide evidence for evolution and a history of life before humans.
Explain geologic time
–The immensity of geologic time is central to understanding the evolution of the Earth and its life.
–Earth goes through long cycles.
–The geologic time scale is the calendar that geologists use to date past events in Earth’s history.
What is uniformitariamism?
Is the main tenet of geology.
– This principle states that the laws of nature have remained unchanged through time and that the processes observed today also operated in the past, though possibly at different rates.
– Therefore, to understand and interpret geologic events from evidence preserved in rocks, geologists must first understand present-day processes in rocks.
Why is the study of historical geology important?
• Understanding how the Earth’s systems work will help ensure the survival of humanity.
• It will help us to understand how our actions affect the delicate balance between these systems.
• Example: Global Climate Change
–Increasing global temperatures over the past decades.
–Increasing temperatures result from greenhouse gas emissions from the utilization of fossil fuels.
–Analyzing mean global temperature changes during the last 130 years and over geologic time.
A mineral is:
–Characteristic physical properties
–Specific chemical composition.
–Rocks are composed of one or more minerals or other solid substances, such as volcanic glass or organics in coal.
Describe the ferromagnesian silicates of minerals
- silicate minerals that contain iron, magnesium, or both.
–Dense and usually dark in color.
Describe the non-ferromagnesian silicates of minerals
- lack iron and magnesium.
–May contain aluminum, calcium, potassium and/or sodium.
– Often light colored.
Describe the carbonate group of minerals
–All carbonate minerals have carbonate (CO³)-² as in calcite (CaCO³) and dolomite (CaMg[CO³]²). –Carbonate minerals are mostly found in the sedimentary rocks limestone and dolostone.
–Carbonates are derived from the shells and hard parts of marine organisms or are precipitated from seawater as evaporites.
Describe the sulfate group of minerals
–All sulfate minerals have the sulfate radical (SO4-²) as in gypsum (CaSO4•2H2O).
–Sulfate minerals are common in deserts, forming from evaporation of water.
Explain the process of the rock cycle
• Uplift and exposure of rocks
• Weathering of rocks to sediments
• Sediment transport and deposition
• Burial of sediments and lithification
• Melting to form magma
• Crystallization of magma
• Volcanic eruptions
Describe sedimentary rocks and explain how they are formed
• Uplift and exposure of rocks
• Weathering of rocks to sediments
• Sediment transport and deposition
• Burial of sediments and lithification
• Melting to form magma
• Crystallization of magma
• Volcanic eruptions
What are the different particle sizes of sedimentary rocks?
–Gravel (>2 mm)
–Sand (1/16-2 mm)
–Silt (1/256 - 1/16 mm)
–Clay (<1/256 mm), Mud is silt and/or clay.
How are sedimentary rocks transported?
- most effective
Where are sedimentary rocks deposited?
–Conversion of unconsolidated sediment to sedimentary rock
–Burial of sediments
- pressure from burial
What are the three classes of sedimentary rocks?
1. detrital clastic
2. detrital sedimentary rocks
3. chemical sedimentary rocks
Describe the sedimentary class - detrital clastic
• Composed of detritus (clasts in sediments) –Chemical/Biochemical
• Precipitation from water
• Biochemical - precipitation by organisms
• Crystalline and/or clastic textures
Composition of Detrital Clastic Rocks
– Quartz, feldspars, clays, and rock fragments are the most common constituents in
detrital sedimentary rocks.
– Composition of detrital
sedimentary rocks depends mostly on the composition of the source rocks in the area
from which their sediment was derived (the source area).
Describe the sedimentary class - detrital sedimentary rocks
• Gravels cement into conglomerates (rounded clasts) and breccias (angular clasts).
• Sands into quartz sandstones and arkoses.
Mudrocks - siltstones, mudstones and claystones.
• Shales - fissile mudstones, which split along closely spaced parallel planes.
Describe the sedimentary class - chemical sedimentary rocks
• Carbonate rocks - limestones and dolostones.
• Evaporites - rock salt and rock gypsum, precipitate from evaporating seawater.
• Chert - spherical masses of silica.
• Coal - biochemical, buried and compressed peat (plants).
– Limestone and dolostone are the most common.
– Carbonates are mostly deposited in warm, shallow seas where the shells of
organisms can accumulate
– Evaporites, such as rock salt and rock gypsum, mostly form from evaporating
What are the processes in lithification?
- packing sediment grains through burial
- reduces volume by 40%
- involves desiccation which is the loss of water from pore spaces resulting from compaction/evaporation
- minerals precipitate from sediment pore fluids to bind together grains
- most common cements = calcite and quartz
What are igneous rocks?
- magma is molten rock below the Earth's surface
- magma solidifies into plutonic or intrusive igneous rocks
-magma erupts as either lava or pyroclastics materials
- lava and pyroclastic materials cool to form volcanic or extrusive igneous rocks
What are the textures in igneous rocks
- phaneritic (coarse-grained) slower cooling
- aphanitic (fine grained) rapid cooling
- very rapid cooling - glassy,obsidian
- porphyritic - phaneritic phenocrysts in aphanitic groundmass, a porphyry
- vesicular - a lot of cavities (vesicles)
What are the different classifications of igneous rocks based on chemistry
- mafic (ferromagnesian minerals dominant)
- felsic (nonferromagnesum minerals dominant)
What are the different classifications of igneous rocks based on texture
- tuff - composed of volcanic ash
- welded tuff - hot volcanic ash fused together
- lapilli - consolidation of larger pyroclastic materials (2-64mm)
- volcanic breccia - blocks (angular) and bombs (smooth)
- pumice - vesicular volcanic glass
- scoria - vesicular, less glassy than pumice
What are metamorphic rocks?
- igneous and sedimentary rocks that are altered without melting
- metamorphism (the change) can be compositional in which new minerals form or textural when minerals become aligned
What causes metamorphism?
- heat (plutons and lava flows, deep burial)
- pressure (deep burial and differential pressure
- fluid activity (water and other liquids and gases)
What are the different types of metamorphism?
- contact metamorphism (plutons)
- regional metamorphism (plate boundaries continent-continent; oceanic- continent)
- dynamic metamorphism (rocks adjacent to faults)
What are the classification of metamorphic rocks?
- foliated (pressure causes platy and elongated minerals to align)
- non-foliated (low pressure contact metamorphci rocks; rocks without platy or elongated minerals)
List different types of foliated metamorphic rocks
List different types of nonfoliated metamorphic rocks
How does plate tectonics relate to the rock cycle?
- Earth's heat contributes to melting and
• Plate tectonics responsible for rock cycle.
• Sediment along continental margins buried
• Convergent plate boundaries result in
mountain building, metamorphism and
• Mountains erode and produce sediments.
Why are sedimentary rocks important?
– They preserve evidence of
ancient surface processes
of their depositional
environments, such as
running water and
– Most fossils occur in them,
which tell us about the
history and evolution of
life. Fossils are also
important in relative
- They contain valuable resources, such as: oil and natural gas, coal, sand and gravel, gypsum, quartz, phosphate, banded iron formation
What are the different sedimentary rock properties observed in field observations?
thickness and lateral extent
- noting the composition and any
- recording relationships with other rocks
What lab investigations can be performed on sedimentary rocks?
identification, and chemical
How do geologists use the principle of uniformitariansim?
to interpret the depositional
environments of sedimentary
rocks. Modern depositional
environments often provide
important insights into ancient
What are the textures in detrital sedimentary rocks?
Texture refers to the size, size distribution, shape and
clasts in detrital sedimentary rocks.
– Grain size in detrital rocks provides information on transport conditions
– The transport of gravels requires glaciers or rapidly flowing water.
– Muds are deposited in low-energy environments.
In terms of texture in detrital sedimentary rocks what is rounding?
– Rounding refers to the removal of sharp edges and corners from
clasts through abrasion.
– Gravels tend to round very quickly as the particles collide during
– Sand grains round with considerable transport.
– Muds that are suspended in water are usually not well-rounded
In terms of texture in detrital sedimentary rocks what is sorting?
Sorting refers to the size variation of clasts in sediments or
– Well-sorted rocks have particles that are about the same size.
– Poorly sorted rocks have a wide range of particle sizes.
– Wind-deposited sands tend to be well-sorted, whereas glaciers carry
almost anything supplied to them and tills are poorly sorted
What are the different sedimentary structures?
– Larger scale features than textures.
– Often form during deposition or shortly
– Important in interpreting depositional
4. ripple marks
5. mud cracks
What is the difference between laminations and beds?
Layers less than 1 cm thick are laminations. Thicker layers
– Laminations are most common in mudrocks, but also occur
in sandstones and limestones.
– Limestones, sandstones, conglomerates may be bedded.
– Bedding planes separate beds.
What is a graded bedding?
- a layer with an upward decrease in grain size.
– In a mixture of sediment and water with waning currents, the largest and heaviest particles settle first and the smallest
particles settle last.
– Graded bedding deposited by waning floods and turbidity
currents on seafloors.
– Turbidity currents are avalanches on the ocean floor.
Describe cross-bedding in sedimentary structures
Cross-bedding - deposition of sand where individual
beds are deposited at an angle to the surface upon which they accumulate.
– Cross-bedding occurs in desert and beach sand dunes, shallow marine
deposits and stream beds.
– Cross-bedding in
sandstones indicate the direction of flow of ancient currents
Describe ripple marks in sedimentary structures
Ripple marks are small scale alternating ridges and troughs on bedding planes, especially in
– Current ripple marks form from
unidirectional winds or flowing
water in streams. They are
asymmetric with a steep
downstream/down wind slope.
– Wave-formed ripple marks tend
to be symmetrical from waves
swashing back and forth.
Describe mud cracks in sedimentary structures
– Mud cracks are polygonal forms resulting from the drying and shrinking of clay-rich sediments.
– Mud cracks form in alternating wet and dry
environments, such as a lakeshore, river
floodplain or mud exposed at low tide on a seashore
What is the geometry of sedimentary rocks?
Refers to the three-dimensional shape of a
sedimentary rock body.
– May be useful in environmental analyses.
– Must be used with caution:
• Many depositional environments produce similar geometries
• Erosion, deformation and sediment compaction during lithification may distort the geometries.
Explain sheet geometry in sedimentary rocks
Rocks from marine transgressions (rising sea level) and
regressions (falling sea level) have a sheet geometry.
• These rocks are far larger in length and width than thickness.
• The origin of the ‘Principle of lateral continuity’ because most preserved sedimentary rocks are marine in nature
Explain elongate or shoestring geometry of sedimentary rocks
Deposited in stream channels and barrier islands
Describe deltas in relation to geometry of sedimentary rocks
• Lens-shaped geometry in profile
• Lobate geometry from above
close to river
mouth (Foreset beds)
– Silt and clay
– Horizontal beds
deposited on top
of foreset beds
during floods (Topset beds)
Why are fossils important when studying sedimentary rocks?
– When found, they are important for determining depositional environments.
– Was the organism buried where it lived (autochthonous) or was
it transported to its burial location (allochthonous)?
ie. Coral reefs buried in place.
ie. Dinosaur carcasses often washed downstream or out to sea.
– What kind of habitat did the organisms originally occupy?
ie. Corals live in warm and shallow marine waters.
Why are microfossils important when studying sedimentary rocks?
• Found in small
well cuttings in
• If not transported,
may be good environmental indicators.
• Sometimes used as
guide fossils in relative dating
What are depositional environments?
• Depositional environments are locations
where sediments accumulate.
• Physical, chemical and biological
processes operate to yield distinctive
• Three main categories:
Describe continental depositional environments in water systems
– Lakes, streams, deserts, and areas covered
by and adjacent to glaciers.
– Fluvial - streams and rivers can be:
• Braided: gravels and sands are dominant
• Meandering: sands and muds, cross-bedding may have:
– Shoestring geometry
– Point bar deposits
Describe continental depositional environments in deserts
• Dunes: cross-bedding
• Alluvial fans: stream deposits
• Playa lakes: muds and evaporites
• Fossils, if present, are terrestrial plants and animals
Describe continental depositional environments in glaciers
• Tills - poorly sorted, mostly found in moraines
• Outwash - sand and gravel, braided streams
• Striations on outcrops
• Varves - annual sediment accumulations in glacial lakes
• Dropstones from icebergs in lakes, seas and oceans
Describe transitional depositional environments in marine processes
• Marine Deltas - fluvial deposits modified by marine processes, such as waves and tides. Deltas may
also occur in large lakes.
• Deposits may contain petroleum.
• Progradation - deltas build by depositing bottomset, foreset and topset beds.
• Terrestrial fossils in topsets and marine or lake fossils in bottomsets.
• Fluvial-dominated: Mississippi River
• Tide-dominated: Ganges-Brahmaputra River
• Wave-dominated: Nile River
Describe transitional depositional environments in barrier islands
• Offshore along marine coastlines.
• Separated from land by a lagoon.
• Sand-rich deposits.
• Subenvironments include: beach sands, dune sands, lagoonal muds.
• Typically require wide continental shelves, microto meso-tidal ranges, ample sediment supply and stable to increasing sea level
Describe transitional depositional environments in tidal flats
• Along many coastlines.
• Covered with seawater at high tide.
• Exposed at low tide.
• May prograde seaward and produce distinctive herring-bone cross-beds, which consist of sets of cross-beds dipping in opposite directions.
Describe marine depositional environments in the continental shelf
• Gently sloping area adjacent to continent.
• High-energy near-shore affected by waves and
tidal currents with cross-bedded sands, waveformed
ripple marks, bioturbation and fossils.
• Low-energy farther off shore - mud and marine
• At the edge of the continental shelf, turbidity
currents transport sediments through submarine
canyons to form submarine fans on the continental
slope and rise
Describe marine depositional environments in the deep seafloor
• Mostly covered by pelagic clay and ooze.
• Major sources of sediment include: wind-blown
dust, volcanic ash and ooze (shells of
• Mid-oceanic ridges.
• Iceberg dropstones in high latitudes
What are characteristics of carbonate marine environments
–Limestones and dolostones.
– Dolostones - limestones altered by
magnesium fluids during diagenesis &
– Micrite - limey mud.
– Some cross-bedding and ripple marks.
– Mud cracks possible in micrite.
– Some carbonates form in lakes.
– Most form in warm, shallow seas.
What are examples of high energy carbonate environments?
• Barriers, such as reefs.
• Reefs include corals, mollusks and sponges.
• Ooids - spherical carbonate grains that lithify to
• Micrite with marine fossils and bioturbation in
What are evaporite depositional environments
– Mostly rock salt and
– Some deposited in
– Most extensive
deposits form in
seas in arid
What is paleogeography?
• Paleogeography involves reconstructing
the past geography of areas and regions.
• Plate tectonics provides the locations of continents over geologic time.
• Rocks and fossils indicate depositional
• Multiple maps of an area at different
times can illustrate marine transgressions
What is stratigraphy?
Stratigraphy is the branch of geology
concerned mostly with the composition,
origin, age relationships, and geographic
extent of layered, or stratified, rocks.
• Stratigraphy mostly deals with
sedimentary rocks because almost all of
them are stratified.
• Geologists determine both the vertical and
lateral relationships of stratified rocks.
What are the key principles of relative dating
relative dating tells us the relative sequence of events
• Principle of Superposition
• Principle of Original Horizontality
• Principle of Lateral Continuity
• Principle of Cross-Cutting Relationships
• Principle of Inclusions
What is the difference between relative dating and absolute dating?
relative dating tells us the relative sequence of events while absolute dating tells us exactly when a rock is formed
What are vertical stratigraphic relationships?
– In vertical successions of sedimentary rocks,
bedding planes separate individual strata from
one another or strata vertically grade from
one rock type to another.
– Rocks below and above a bedding plane vary in composition, texture, and/or color, which result from a rapid change in sedimentation or
perhaps a period of nondeposition and
erosion followed by renewed deposition.
What information can be learned from the Principle of Superposition?
used to determine the
relative ages of undeformed overlying and underlying sedimentary layers
- If the layers have been deformed by faulting
or folding, relative dating becomes more
difficult. Other sedimentary structures or
fossils can help to resolve relative dating
What is the Principle of Inclusions?
The Principle of Inclusions is another
method to determine relative ages
• The principle states that inclusions or rock
fragments within a rock are older than the
What are unconformities?
are surfaces of erosion
and/or nondeposition within sedimentary
Describe depositions within conformable strata
more or less continuous.
• Unconformities are surfaces of erosion
and/or nondeposition within sedimentary
• Erosion and/or nondeposition may have
lasted for millions of years.
• A hiatus is an interval of geologic time not
represented by strata
What are the three types of unconformities?
– Angular unconformity
separates younger from older sedimentary strata that are parallel to each other.
is an erosional surface cut into igneous or
metamorphic rocks and overlain by younger sedimentary
Explain angular unconformity
is an erosional surface on tilted or folded rocks, over which younger sedimentary
rocks were deposited.
Explain the Principle of Lateral Continuity
• Layers of sediments or sedimentary rocks extend outward in all directions until they terminate.
• Termination may be due to erosion, faults, or the rocks simply pinch out or i
ntertongue with adjacent rocks.
• Lateral gradation - rocks laterally change in composition and/or texture into another rock type.
Explain the role of facies in lateral relationships
– Both intertonguing and lateral gradation
indicate different depositional processes in adjacent environments.
– For example, in a continental shelf, sand may be deposited in a nearshore marine
environment and mud in a quieter offshore
– Deposition in each of these laterally adjacent
environments yields a sedimentary facies.
What are sedimentary facies?
a body of sediment with
distinctive physical, chemical, and biological
– Any attribute of sedimentary rocks that
makes them recognizably different from laterally adjacent rocks of about the same age is sufficient to establish a sedimentary
• Sedimentary facies are used to identify
ancient changes in sea level, called
marine transgressions and regressions.
• A marine transgression occurs when sea
level rises relative to the land, resulting in
offshore facies overlying nearshore facies.
What is a marine regression?
caused when sea
level falls relative to the land, results in
nearshore facies overlying offshore facies.
Explain the extent, rates and different causes of marine transgressions and regressions
– Since the Neoproterozoic (1,000 Ma-), six
widespread marine transgressions and
regressions have occurred in North America.
– On average, the transgression rate was about 5 cm/year, but included minor reversals.
– Transgressions caused by tectonic
subsidence, melting glaciers, and increased
seafloor spreading, where the excess heat
causes oceanic ridges to expand and displace
water onto the continents.
– Regressions result from tectonic movements
elevating land, expanding glaciers removing
seawater, and decreased seafloor spreading.
Explain and describe a fossil
• Fossils are the remains or traces of
prehistoric organisms preserved in rocks.
• They usually occur in sedimentary rocks.
• Fossils provide information on ages,
depositional environments and biological
• Fossils also provide relative ages between
separated columnar sections of rocks.
What are the two categories of fossils?
– Body fossils - shells, bones, teeth, and rarely soft parts.
– Trace fossils - tracks, trails, burrows, nests,
How does a fossil form?
– Favorable conditions for fossilization
• Durable body parts
• Lived where burial in sediment was likely
• Avoided decay, scavenging and metamorphism
What are the different types of fossil preservation?
– Unaltered body fossils - largely retain their original structure and composition
– Altered body fossils - structure and
– Trace fossils
– Molds and casts
• Mold - an impression of an organism
• Cast - minerals or sediments fill the mold, a replica
of the original
Explain the Principle of Fossil Succession
– William Smith (1769-1839) established the
Principle of Fossil Succession.
– The principle states that fossil assemblages
(groups of fossils) succeed one another
through time in a regular and predictable
– Because the succession of fossils in the
geologic record is ordered and not random,
they can be used for relative dating
What two times do fossils of an extinct organism tell use
when they first appeared and when
they became extinct
Explain the relative geologic time scale
• Investigations by naturalists beginning in
the 1830s resulted in the recognition of
rock bodies called systems, which led to
the construction of a composite geologic
column that is the basis of the relative
geologic time scale.
• In the 1830s, Adam Sedgwick studied
rocks in northern Wales and described the
• Sir Roderick Impey Murchison named the
younger Silurian System in southern
• Murchison, unlike Sedgwick, carefully
studied the fossils and the Silurian System
could be identified elsewhere.
• When Sedgwick and Murchison published
their results in 1835, it was discovered that
their systems overlapped.
• The dispute was resolved in 1879, when
Charles Lapworth suggested that the
rocks in the disputed area be assigned to
a new system, the Ordovician.
• Using superposition and fossil
assemblages, other systems were defined
in the 19th century and the relative
geologic time scale was established.
• In the 20th century, radiometric dating
allowed absolute dates to be assigned to
the various systems of the geologic time
What is a lithostratigraphic unit?
is defined by its rock
type(s) without consideration of its age or
mode of origin.
– The basic lithostratigraphic unit is the
– A formation is a mappable body of rock with
distinctive upper and lower boundaries.
Explain how stratigraphic units defined by their content
– Formations may contain one rock type (e.g., Redwall Limestone) or a variety of related rock types (e.g., Morrison Formation).
– Formations may include igneous and
metamorphic rocks, and not just sedimentary rocks.
– Formations are divided into members and beds, and grouped into groups and supergroups.
– Biostratigraphic units are defined by their
fossil content without regard to their rock type or time of origin.
– The basic unit is the biozone.
– Their boundaries do not necessarily
correspond to lithostratigraphic units
What stratigraphic units are expressed or related to geologic time?
– Time-stratigraphic (chonostratigraphic) unit,
indicates that a particular rock unit formed during a particular time interval.
– The basic time-stratigraphic unit is the
– A stratotype is the rocks in an area where the system was first described. Fossils are used to identify a system beyond its stratotype.
– Time units designate certain intervals of
geologic time. They have corresponding timestratigraphic
– The period is the basic unit of geologic time.
– An era consists of two or more periods.
– An eon is two or more eras.
– Periods are divided into epochs and ages.
• Correlation refers to matching geologic
features between two or more areas.
• In lithostratigraphic correlation, rock units
are correlated without regard to their age.
• In time-stratigraphic correlation, systems
may be correlated beyond their stratotypes
by applying the Principle of Fossil
What is lithostratigraphic correlation?
– Can demonstrate that a formation or other lithostratigraphic unit was once continuous over a given area.
– Lithostratigraphic correlation is done with
outcrop studies, well cores and cuttings from drilling operations and geophysical data.
Explain time-stratigraphic correlation?
– Biozones are effective in time-stratigraphic
– Range zone - a type of biozone that
describes the geologic range of a fossil
group; that is, from the time they came into
existence to when they became extinct
– Interval zones define the first and last
occurrence of a fossil.
– Concurrent range zones are more useful and are established by plotting the overlapping ranges of two or more fossils.
– Correlating concurrent range zones is probably the most accurate method to determine time equivalence between
sedimentary rocks in widely separated areas.
– Some events can be used to demonstrate
• Lava flows and volcanic ash falls. Each formed rapidly at a specific time.
– Precambrian rocks lack useful fossils.
Radiometric dating is most useful.
Describe the properties of useful fossils
– Useful fossils or guide fossils have the
• Easily identified.
• Geographically widespread.
• Lived for brief periods of geologic time.
• Atrypa and Paradoxides are good guide fossils.
Lingula is not.
Explain dating of sedimentary rocks
• Most sedimentary rocks cannot be dated
with radiometric methods.
• Maximum, minimum or age ranges of
sedimentary rocks may be obtained from
radiometric dates on dikes that cross-cut
the rocks or any volcanic ash beds, lava
flows, and sills that occur between the
sedimentary rock layers.
• Radiometric dates on ash falls, plutons,
lava flows and metamorphic rocks
associated with fossil-bearing sedimentary
rocks have provided absolute ages for the
periods of the geologic time scale.
• Radiometric dates on igneous and
metamorphic rocks associated with fossilbearing
rocks also may provide age ranges for the fossils.
• For example, radiometric dates on ash beds in the Bearpaw Formation of
Saskatchewan, Canada indicate that the
Baculites reesidei biostratigraphic zone in
the formation is about 72 to 73 million
Explain why plate tectonics is important to geology
Plate tectonics is the unifying theory of
geology, tying together many seemingly
unrelated geologic phenomena and
illustrating why Earth is a dynamic planet
of interacting subsystems and cycles
What were the early ideas about the continental drift?
• Continental movement was first suggested
when it was noticed that the coastlines of
Africa and South America appear to fit
together like pieces of a puzzle.
• It was suggested that they were once
joined together and then drifted apart.
What did Edward Suess contribute to our early understanding of continental drift?
- In the late 19th
Suess noticed that the
Late Paleozoic plant
was located in India,
Australia, South Africa
and South America.
- How did this fossil get distributed in these widely separated
areas with very
Explain Alfred Wegener's continental drift hypothesis
- proposed in 1912
- He postulated that
all landmasses were originally united into a
supercontinent named Pangaea
- Pangaea consisted of a northern landmass
called Laurasia and a
called Gondwana. As
Pangaea broke up, the
moved to their present day locations
What evidence is there for Wegener's theory of continental drift?
1. Continental fit
- There are close
fits between the
depths of about
2. Similarity of rock sequences and mountain ranges
- – Marine, nonmarine, and glacial rock sequences of
Pennsylvanian to Jurassic age (318-146 Ma) are
nearly identical on all the Gondwana continents
- The trend of several major mountain ranges
produces a continuous mountain range when the continents are positioned next to each other as they were during the formation of Pangaea
3. Glacial evidence
- Tillites (lithified tills) and striations on the
bedrock beneath the till provide evidence of
glaciation at the same time on all the
Gondwana continents, with South Africa
located at the South Pole
4. Fossil evidence
- The distribution of certain fossils in Gondwana
supports continental drift.
- These fossils include the Glossopteris fern
and Mesosaurus, a fresh water reptile
- If the continents have always been in their
present positions, how did these organisms
migrate between South America, Africa, India,
Antarctica and Australia?
Wegener could not provide a convincing
mechanism to demonstrate ‘how’ the
continents could have moved. Continental drift was largely ignored until
Describe earth's magnetic field
- Earth's magnetic field consists of north
and south poles, like a bar magnet.
- Earth's magnetic field is probably due to
the movement of molten iron in the Earth's outer core
- Locations of the Earth's magnetic poles
and the strength of the Earth's magnetic
field vary over time
- As of 2017, the Earth’s North magnetic
pole is about 3.5° from the geographic
North pole, whereas the South magnetic
pole is about 25.5° from the geographic
- When lavas cool below the Curie point,
their magnetic iron minerals align
themselves with the Earth's magnetic field
- As long as the rock is not subsequently
heated above the Curie point, it will
preserve its remnant magnetism
- Paleomagnetism is the remnant
magnetism in ancient rocks recording the
direction and intensity of the Earth’s
magnetic field at the time of the rock’s
What is the curie point?
is the temperature at
which hot iron-bearing minerals cool
enough to gain magnetism
How did paleomagnetic studies impact interest on the continental drift theory?
- They indicated that either the magnetic poles had wandered and each continent had its own pole (an impossibility), or
- The continents had moved over time. If the continents moved into different positions
relative to each other, the separate poles
could be resolved into one
Explain magnetic field reversal
Earth’s present magnetic field is
- Normal - with the north and south magnetic poles located approximately at the north and south geographic poles, respectively
- At various times in the geologic past, Earth’s
magnetic field has completely reversed
-Reversed - the magnetic south pole is near the geographic north pole and the magnetic north pole is near the geographic south pole
The existence of magnetic reversals was
discovered in continental lava flows by:
– Age dating (radiometric)
– Determining the orientation of the remnant
What is the theory of seafloor spreading?
- proposed in 1962 by Harry Hess
- He suggested that the seafloor separates at oceanic ridges, where new crust is formed by upwelling magma
- As the magma cools, the newly formed
oceanic crust moves laterally away from the
How was seafloor spreading confirmed?
- Seafloor spreading was confirmed by
magnetic anomalies in the ocean crust that
were both parallel to and symmetric around
the ocean ridges
- This indicates that new oceanic crust forms along the spreading ridges
- Deep sea drilling project also confirmed spreading through ages of fossils in ocean sediments and radiometric dating of ocean floor volcanic rocks (the oceanic crust is youngest at the spreading ridges and oldest at the farthest points from the ridges)
Explain why the theory of plate tectonics is now widely accepted and why it is known as a unifying theory
- The theory is widely accepted because it
explains so many geologic phenomena,
including: volcanism, seismicity, mountain
building, climatic changes, animal and plant distributions in the past and present, and the distributions of natural resources
- For these reasons, it is known as a unifying theory
Explain the composition of the lithosphere based on the plate tectonics theory
- the lithosphere is divided into different plates
- seven major plates and many minor ones
- Some plates include continental as well as
- The rigid lithosphere overlies the plastic
asthenosphere, and some type of heat transfer system within the asthenosphere
moves the plates
- As the plates move over the asthenosphere, they separate mostly at
oceanic ridges, and collide and subduct
into the Earth’s interior at oceanic
In what era did plate tectonics begin to operate
What are the three types of plate boundaries
Describe a divergent boundary form
– Divergent boundaries form when two plates
move away from each other.
– New crust forms at the opening rift.
– Most divergent boundaries occur along the
crests of oceanic ridges.
– They are also present under continents during
the early stages of continental breakup.
What are the properties of a divergent boundary
- Characteristic features of ancient continental
rifting include: faulting, dikes, sills, lava flows,
and thick sedimentary sequences within rift
– Pillow lavas and associated deep-sea
sediments are evidence of ancient spreading
What are examples of divergent boundaries or where are they found
- Modern example: East Africa.
– Initial stages of continental breakup.
– Rift valleys and volcanism.
– Rift valleys expand and create seas, such as
– As divergence continues, seas may expand
into oceans and continents have passive
What is a convergent boundary
where two plates collide
What are the three types of convergent boundaries?
1. oceanic - oceanic boundary
2. oceanic - continental boundary
3. continental - continental boundary
Describe oceanic - oceanic convergent boundaries
- two oceanic plates
collide, one ocean plate will subduct beneath the margin of the other plate
- An oceanic trench forms parallel to the
volcanic island arc where the subduction
– Volcanoes result from rising magma produced by the partial melting of the subducting plate.
– Japan and the Aleutian Islands of Alaska
Describe oceanic-continental convergent boundaries
– An oceanic plate and a continental plate
converge, with the denser oceanic plate
subducting under the continental plate.
– Like an oceanic-oceanic boundary, a chain of
volcanoes forms on the nonsubducted plate.
– Andes Mountains of South America
Describe continental-continental convergent boundaries
– Two continents converge, the ocean floor
separating them subducts, the two continents
collide. Neither plate will subduct.
– When the two continents collide, they are
welded together to form an interior mountain
– Himalayan Mountains of Asia
How can you recognize ancient convergent plate boundaries on continents?
– During subduction, part of the oceanic crust ay accrete onto continents.
– Intensely deformed rocks, andesite lavas, and ophiolites are all evidence of ancient
subduction zones, marking former convergent
Describe transform boundaries
– Plates slide laterally past each other along
– San Andreas Fault in California, USA.
– Other transform faults connect oceanic ridge segments
What are hot spots?
– A hot spot is the location on Earth’s surface
where a stationary column of magma, originating deep within the Earth (possible
near the mantle-outer core boundary) slowly
rises to the surface and causes volcanism.
– Hot spots occur in Hawaii, Iceland, Yellowstone National Park in Wyoming, and elsewhere
- Hot spot plumes apparently remain
stationary within the mantle while plates move over them.
- The resulting hot spot leaves a trail of
extinct and progressively older volcanoes
that record the movement of the plate.
- Seen in the Emperor Seamount-Hawaiian
How are plate movement and motion determined?
- Hot spots may be used to determine the absolute motion of plates. They provide an apparently fixed reference point from
which the rate and direction of plate
movement can be measured.
- To determine the average rate of plate
Divide the distance from an oceanic ridge axis
to any magnetic anomaly in the crust of the
seafloor by the age of that anomaly.
- Satellite-laser ranging techniques are also
used to determine the current rate of
movement and relative motion of one plate
with respect to another
What causes plates to move?
- Most geologists agree that some type of convective heat system is the basic process responsible for plate motion.
– Radioactive decay in the Earth's interior provides heat for convection.
– Additional heat comes from the core
What is the mantle convection cell model?
- Spreading ridges: Hot ascending limbs of
– Trenches: Cooled part of convention cells
What is the gravity-driven plate motion model?
- Besides convection, gravity-driven mechanisms may have a major role.
– “Slab-pull” involves pulling the plate behind a subducting cold slab of lithosphere.
– “Ridge-push” involves gravity pushing the
oceanic lithosphere away from the higher
spreading ridges and toward the subduction
What is orogeny?
episode of intense rock
deformation or mountain building.
• Results from the compressive forces of
– Folds and faults sediments and volcanic rocks.
– Deeper rocks are metamorphosed.
– Magmas form
How does plate tectonics impact the distribution of life?
• Organisms occupy biotic provinces
controlled mostly by:
– Geographic barriers
• Plate movements create mountains and
continental barriers that influence climate
and biological evolution
• Plate Tectonics and Biological Evolution in
– Formation of Panama by plate movements
about 5 million years ago isolated Caribbean
and Pacific marine organisms promoting
– North American land animals migrated to
South America, causing extinctions of South
How does plate tectonics impact the distribution of natural resources?
– During the Mesozoic Era, much of the Middle
East was a broad marine shelf near the
– Countless microorganisms lived in the warm
surface waters, died and accumulated in
– Burial of the organic-rich sediments from
subduction created the right amount of heat to
– Plate collisions between Iran and the Arabian
Plate folded rocks and created traps for the
petroleum to accumulate
• Mineral Deposits
– Many metallic mineral deposits are related to
igneous and associated hydrothermal activity
in convergent and divergent plate boundaries.
– Copper, iron, lead, zinc, gold and silver ore
deposits are associated with plate
– Copper ores along the convergent boundaries
of the west coasts of the Americas
What were Darwin's observations on the Galapagos islands?
- He observed that animals descend (with
modification) from ancestral species.
- Darwin postulated that the 13 species of
finches on the Galapagos Islands and the
one on Cocos Island evolved from a
common ancestor species that reached
the islands long ago
- The islands scarcity of food forced the
finches to evolve new physical
characteristics, especially beak shape, to
What is Darwin's theory of evolution?
Darwin was convinced that organisms descend with modification from ancestors
Why is evolution important to Geology?
• Evolution is fundamental to the study of
biology and paleontology, the life history
revealed in fossils.
• Evolution also contributes to the unifying
theory of plate tectonics
Explain large scale and small scale evolution
• Biological evolution, or descend with modification from ancestors, may be
– Changing genetic makeup of populations
from generation to generation.
• Biological evolution may be large-scale:
– Origin of a new species from a common
• Biological evolution does NOT explain the
origin of life on Earth
• Biological evolution describes how living
organisms have changed since life first
appeared on Earth
How did evolution disprove Genesis?
Beginning in the 18th
sought evidence for
What was James Hutton's role in disproving Genesis?
and others concluded
that the Earth was
far older than the
What was Georges Cuvier role in disproving Genesis?
many plants and
animals are now
extinct. How was
that possible if
Noah succeeded in
saving them from
What was Jean-Baptiste de Lamarck (1744-
1829) ideas on evolution?
– Lamarck’s proposal of inheritance of acquired characteristics was the first formal explanation for the
theory of evolution to be taken seriously.
– This idea states that new
characteristics arise in organisms because of their needs and, somehow, these characteristics are
passed on to their descendants.
This is inheritance of acquired characteristics
– In an ancestral population of short-necked giraffes, neckstretching to browse in trees results in longer necks, which are then inherited by their
– Lamarck's ideas were finally discredited with the discovery of genes, which cannot be naturally altered by any effort of an organism during its lifetime.
Explain Darwin and Alfred Wallace's views on evolution?
– In 1859, Charles Robert
Darwin and Alfred
Russel Wallace published their views on evolution and proposed natural selection as the mechanism for evolutionary change
– Darwin’s observations of variation in natural populations and artificial selection, as well as his reading of Thomas Malthus’s essay on
population, helped him formulate the idea that
natural processes select favorable variants for survival
Explain the theory of natural selection?
- Organisms in all populations possess
heritable variations, such as size, speed,
agility, color, etc.
– Some variations are more favorable than
others; that is, some variant types have a
competitive edge in acquiring resources
and/or avoiding predators
– Those with favorable variations are more
likely to survive to reproductive maturity
and pass on their favorable variations.
– "Survival of the fittest" is misleading.
• In some cases, the smallest and easiest to conceal survive, whereas the biggest, strongest and fastest do not
- Having favorable variations does not guarantee that an individual will
live long enough to reproduce and pass on it’s genes.
– However, in a population of perhaps thousands, those with favorable
variations are more likely to survive and reproduce.
– Sexual selection is a special type of natural selection, where animals
compete for mates
- Natural selection can explain the origins of
complex features, such as eyes and wings.
• Even eyes that are no more than light-sensitive
spots are functional.
• Poorly developed wings are useful in incline
Explain Mendel's experiments which are described as the birth of genetics
- Gregor Mendel’s breeding
experiments in the 1860s with garden peas
– Mendel concluded that traits, such as flower color, are controlled by a pair of
factors, or what we now call genes.
– Genes that control the same trait occur in alternate forms now called
- Genes that control traits do not blend during
inheritance, even though they may not be
expressed in every generation.
– Most traits are controlled by many genes
and some genes show incomplete
What variables was Mendel not aware of when doing his experiments?
– Mendel was unaware of:
• Mutations (changes in genetic material).
• Some genes control the expression of other genes.
• Hox genes, which regulate the development of
major body segments.
What are chromosomes?
- Chromosomes are complex, double- stranded
helical molecules of
deoxyribonucleic acid (DNA).
– Chromosomes are found in the cells of all
What is a gene?
– Specific segments of the DNA molecule are
hereditary units called genes
How are chromosomes organized in organisms?
– The number of
specific for each species.
• Fruit flies have 8 (4 pair).
• Humans have 46 (23 pair)
• Domestic horses have 64.
– Chromosomes are found
in pairs carrying genes
controlling the same
Explain how sex cells are organized in organisms
• Pollen and ovules in plants
• Sperm and eggs in
– The production of sex
cells results when cells
undergo a type of cell
division called meiosis.
– Meiosis yields cells with
only one chromosome
of each pair
– During reproduction, a sperm fertilizes an egg
(or pollen fertilizes an ovule) yielding an egg
or ovule with a full set of chromosomes typical
for that species.
– A fertilized egg then grows by mitosis, where
the cells are simply duplicated without any
reduction in the chromosome number.
– Sexual reproduction and mutations
account for most of the variation in a
What is the modern view of evolution?
Development of Neo-Darwinism in the 20th
– Genetics was incorporated into the theory of
evolution, including the chromosome theory of
inheritance and mutations.
– Lamarck's ideas were discredited. Populations
rather than individuals evolve.
– Importance of natural selection reaffirmed.
– New ideas continue to develop on speciation,
genetic drift, lateral gene transfer, epigenetics,
and other issues
What caused variation?
– Mutations - changes in chromosomes or
– Chromosomal mutation - affects large
segment of a chromosome.
– Point mutation - a change in a gene.
– Point mutations in sex cells are inheritable
Describe the benefits or harm of mutations?
Mutations are random and may
be harmful, beneficial, or
– If a species is well adapted to its environment, most mutations would not be useful and could
• Some plants of a species develop resistance to contaminants in soils
around mines, but die in
• Mutations for contaminant
resistance probably occur
repeatedly in a population, but only become beneficial if contaminated soils are present.
Mutations may result from chemicals,
radiation, and extreme temperatures.
– Some mutations are spontaneous and have
no known mutagen.
– Sexual reproduction and mutations account
for most variations in populations
Explain genetic drift
Genetic drift, a random change in the genetic
makeup of a population due to chance, may
also be important.
– Genetic drift is probably more important in
small populations, such as those that occur in
isolated and remote areas
new species arising from an
ancestral species. Well documented
Species - a population of similar individuals
that interbreed in nature and produce fertile
offspring. This definition does not apply to
How does speciation impact the rate of evolution?
– Microevolution - evolutionary changes
within a species.
• House sparrows in North America.
• Organisms develop resistance to
contaminants and pesticides.
– Macroevolution - origins of new species,
genera, families, orders, and classes.
• Amphibians from fish.
• Mammals from mammal-like reptiles.
• Whales from land-dwelling
– Macroevolution encompasses greater
changes than microevolution.
– Accumulative effects of microevolution
account for macroevolution.
– Macroevolution and microevolution only vary
in degree of change
- Speciation involves a change in the genetic
makeup of a population.
– Populations and not individuals evolve
What are possible causes of speciation?
• Allopatric speciation
• Phyletic gradualism
• Punctuated equilibrium
Explain allopatric speciation
When a group is isolated from its parent population, gene flow is restricted
or eliminated, and the isolated group is subjected to different
– Causes of isolation:
• Mountain barriers
• Rising sea level
– Disagreement over how rapidly a new species might evolve because of it
Explain phyletic gradualism
of minor changes brings about a new species
Explain punctuated equilibrium
Little or no change
in a species occurs during most of its history,
but evolution to a new species occurs rapidly,
perhaps in only a few thousand years.
Punctuated equilibrium is controversial among
– Polyploidy - Some new plant species arise by
the doubling of chromosomes
What is the first step in speciation usually?
1. Isolation or partial isolation of a species is
often the first step to speciation. Common in:
What is divergent evolution?
Divergent evolution involves an ancestral
stock giving rise to diverse species.
• Mammals diverging from a common ancestor
during the Late Mesozoic to give rise to diverse
mammals, such as: platypuses, armadillos,
rodents, bats, primates, whales, and rhinoceroses.
• Descendants are very different than their
What is convergent and parallel evolution?
Convergent and parallel evolution - similar
adaptations arise in different groups.
• Convergent evolution - development of similar
characteristics in distantly related organisms.
• Parallel evolution - development of similar
characteristics in closely related organisms.
• Convergent and parallel evolution differ in degree.
Not always easy to distinguish.
• Similar characteristics develop independently
because the organisms live in comparable
Examples of Convergent evolution
• Mammals in North and South America
• Tasmanian "wolf" (marsupial) and dogs and
• Sharks, ichthyosaurs (extinct marine reptiles), and
What is Mosaic evolution?
characteristics, but still have characteristics of
What are some evolutionary trends?
– Evolution does not affect all aspects of an
– A key feature of a descendant group may
appear before other features.
• Oldest known bird had features and a furcula
(wishbone), but also retained many characteristics
of its reptile ancestors
- Titanotheres - body size, skull shape, and
development of large nasal horns over time.
- Evolutionary trends in camels - increased body
size, longer limbs, reduction in number of toes,
loss of front teeth, and changes in chewing teeth
Evolutionary trends are complex, may reverse, and
not all occur at the same rate.
• Horses - general increase in body size, but some
extinct species showed a size decrease.
• Trends due to adaptations to changing
environments or when organisms enter new
- Some organisms, such as the coelacanth
Latimeria, the ginkgo tree and other "living fossils",
show little evolutionary change between fossilized
parts and analogous parts on living individuals
(e.g., bones, shells or leaves).
• The extent of any evolutionary changes in soft
parts, such as the immune system, are unknown.
• Most "living fossils" are generalized organisms,
which means that they can live under a wide
variety of environmental conditions or live in
environments that have not significantly changed
What is phylogeny?
Explain why evolution by natural selection not entirely random
• First, variation must be present or arise in a
population. Mutations are random.
• Second, individuals with favorable variations are
most likely to survive and reproduce. This is not
is another type of biological
analysis where organisms are grouped based
on their evolutionary novelties (like hair) as
opposed to primitive characteristics
– Scientists are increasingly using cladistic
analyses to determine evolutionary
relationships among organisms
- Cladistics used to predict evolutionary
relationships between whales and even-toed
hoofed mammals (deer, hippos, etc.)
– Cladistic analysis of Pacific yews discovered a
compound used to treat cancer.
– Cladistics of fossil organisms must be
carefully done. Convergent evolution may
complicate the analysis
A cladogram is a diagram that shows the
relationships between members of a clade, a
group of related organisms, including its most
recent common ancestor
- Mass extinctions are times of accelerated
extinction rates and losses in Earth’s biologic
– Mass extinctions have occurred several times
in the Earth’s history and form the basis of the
geologic time scale.
– Likewise, new species are constantly arising,
often to fill niches left by extinct species
- 99% of all species are now extinct.
Background extinctions take place continually
What evidence is there for evolutionary theory?
– Classification of organisms
– Comparative anatomy
– Fossil record
- molecular biology
- the theory can make predictions e.g. Evolutionary theory predicts that closely
related species, such as wolves and coyotes,
should have similar anatomy, biochemistry,
genetics, and embryonic development. They
Explain how species are classified
Two-part genus and species name developed
by Carolus Linnaeus (1707-1778).
– Linnaeus' classification of organisms
becomes more inclusive from species to
– Linnaeus recognized shared characteristics
among organisms, but he believed that
species were created and immutable
– Linnaeus' classification gives us information
about the biological world, but it does not
always reflect evolutionary relationships.
– Cladograms allow us to group organisms with
similar characteristics and better determine
Explain the biological evidence to support evolutionary theory
1. All organisms have similarities suggesting a they evolved from a common ancestor:
2. Vestigial structures are remnants of structures
in organisms that were fully functional in their
3. Some vestigial structures are fully functional,
but perform totally different functions than
they did in the ancestors.
• The incus and malleus of the mammalian middle
ear were derived from the articular and quadrate
bones that formed the joint between the jaw and
skull in mammal-like
4. Microevolution in living organisms
.5. Biogeography - the geographic distribution of
organisms both past and present.
• Island flora and fauna most closely resemble those
of nearby islands or the nearest continent.
• Some animals arrive on remote islands by flying or
floating on vegetation.
• Evolution of reproductively isolated species
What are similarities all organisms have that suggest they evolved from a common ancestor
• Organisms are carbon-based.
• Their chromosomes consist of DNA.
• Their cells synthesize proteins in the same way.
• Blood proteins are similar among primates.
• Biochemical tests support the fossil record that
birds evolved from reptiles.
• Similar embryonic development
• Homologous structures in limb bones of birds,
reptiles and mammals, but different or only
analogous structures in insects.
• Analogous structures, such as legs and wings on
insects and birds, look similar and may serve the
same purpose, but they are not similar in structure
and evolutionary development
What are examples that vestigial structures are remnants of structures
in organisms that were fully functional in their
• Examples would be the ‘dewclaw’ in a dog,
‘wisdom teeth’ in a human, and the pelvis in the
• The human jaw is now too short to accommodate
the ancestral number of teeth
Explain microevolution in living organisms
• Adaptation of plants to contaminated soils
• Insects develop resistance to pesticides
• Bacteria develop resistance to antibiotics
• Some variant types are more likely to survive and
reproduce, bringing about a genetic change
What do fossils tell us about evolution?
Fossils show a sequence in the geologic
record that is explained by evolution:
– One-celled organisms appeared before multicelled
– Invertebrates appeared before invertebrates.
– Fish were followed by amphibians, reptiles,
mammals, and birds.
Many organisms are not well-preserved in
the fossil record, but the available fossils
For example fossils indicate that horses, rhinoceroses,
and tapirs had a common ancestor.
– Evolution predicts that as we trace these
animals back through the fossil record, it
should be more difficult to distinguish them.
– Indeed, the earliest members of each are very
similar and differing mostly in size and details
of their teeth
Are there missing links in the fossil record?
Although there are missing links between
ancestors and their descendants, there are
many fossils as close to being intermediate,
or transitional, between groups as we could
ever hope to find.
• Fish and amphibians
• Mammal-like reptiles and mammals
How old is the earth?
4.6 billion years old (bya)
What is the largest unit of time on Earth?
- Precambrian – literally “before” the Cambrian, not a formal interval
- It lasted from 4.6 billion to 542 million years ago
- Precambrian also refers to rocks of that age
- constitutes 88% of all geologic time
What eons is the precambrian period divided into?
Archean and Proterozoic
- Because of a lack of fossils, the divisions
of the Precambrian are based on absolute
dates rather than time-stratigraphic units.
What is the Hadean?
- refers to the
earliest part of the Earth's history for which
there are no known rocks
- The Hadean Eon occurred from the origin
of the Earth about 4.6 Ga to about 4.0 Ga
What happened in the Hadean Eon?
- The Earth accreted by sweeping up planetesimals. Meteor and comet
bombardments occurred until about 3.8 Ga.
• A Mars-sized planet probably struck Earth
about 4.4-4.6 Ga and injected material that
coalesced into the Moon
•Initially, an Earth day may have been as short as 10 hours.
• Friction caused by the
Moon on the oceans and continents slowed down the Earth's rotation and slowly lengthened the day
• The Moon was initially much closer to the Earth. It continues to recede from the Earth at a few centimetres per year.
• Abundant radionuclides produced a lot of
heat and resulted in widespread volcanism
• The core, mantle, and an ultramafic crust differentiated.
• Oceans may have begun to form by 4.4 bya (O isotopy on zircons).
• Volcanic gases created an atmosphere, but there was little or no free oxygen (O2).
• The first crust(s) were ultramafic to mafic,
but weathering produced sediments richer
• Partial melting of mafic rocks also produced more silica-rich magmas and
• Subduction of crust formed small island arcs, which collided and accreted into the first proto-continents
How was the Earth's moon formed?
Giant Impact Hypothesis:
1. the moon formed by collision of a Mars-sized
body callled Theia with Earth ~4.5 Ga when the Earth was still semi-molten
2. Intense heat is created by the impact and huge amounts of debris from both Theia and Earth are thrown into space
3. The debris coalesces as it orbits the earth
4. The Moon is formed from this debris
Explain radioactive decay
•Some isotopes have unstable nuclei
• Nuclei spontaneously break apart (decay) to give off energy as particles or rays
What are the three common mechanisms of radioactive decay?
1. Alpha Emission =
parent nucleus emits an
alpha particle which is
2 protons and 2 neutrons
2. Beta Emission =
Parent nucleus emits a
beta particle which is
an electron that was part
of a neutron
3. Electron capture:
proton captures an
electron to become a
What was the Archean history?
The Archean includes 32.6% of geologic
Why are the archean rocks difficult to interpret?
– Most are metamorphosed and completely
– Most are currently deeply buried and difficult
– They contain few (or no) fossils
Describe a craton
- All continents have an ancient, stable craton
made up of a Precambrian shield and platform
- Cratons are the foundations or nuclei of the
- North America consists of the Superior, Hearne, Rae, and Slave cratons of the
Canadian Shield. -
-Archean and Proterozoic rocks occur in the
cratons, which include several episodes of
deformation accompanied by igneous activity,
metamorphism, and mountain building
- The oldest known rocks are the Acasta
Gneiss of the Northwest Territories, Canada,
which is about 4.0 bya; and Faux Amphibolites in Northern Quebec: 4.28 bya.
What are shields?
- Areas of exposed Precambrian rocks
constitute the shields.
- About 22% of the Earth's exposed Precambrian rocks are Archean.
Archean rocks are:
– Most are greenstone belts and the more common granite-gneiss complexes.
– Other rocks include peridotites and sedimentary rocks, all of which have been
What are platforms?
Platforms consist of buried Precambrian rocks.
– Three main rock associations:
• Lower - mostly volcanic
• Middle - mostly volcanic
• Upper - mostly sedimentary.
– Synclinal structure, 40-250 km wide, 120-180 km
– Oldest well-described is in Greenland, 3.7-3.8 Ga.
– Pillow basalts from underwater eruptions are
common (but ultramafic!)
– Komatiites - ultramafic lava flows, very hot, more than 1600oC. Probably produced by high radiogenic heat in the mantle. Mantle is too cool for eruption of komatiites today.
– Belts intruded by granitic magmas and faulted.
– Greenstones - typically low-grade metamorphism.
– Sedimentary rocks in the upper unit include:
• Graywackes - sandstones rich in clay and rock
• Argillite – low-grade metamorphosed mudstones.
– Other sedimentary rocks:
• Sandstones, conglomerates, chert, carbonates
• Banded iron formations.
Where are greenbelts located in North America
– Mostly in Superior and Slave cratons.
– Some in Michigan, Minnesota, and Wyoming.
– Mostly 2.5-2.7 bya.
– Abitibi greenstone belt of Ontario and
Quebec, Canada has gold, copper and zinc
Explain the evolution of greenbelts
– Originated in several tectonic settings:
• Oceanic plateaus
• Rifted continental margins
• Rifts within continents
• Back-arc basins that subsequently closed.
– Back-arc basin model explains the origins of
some of them
– The origins of other greenstone belts are
explained by the intracontinental rift model.
Explain how archean plate tectonics lead to the origin of cratons
– Most geologists believe that plate tectonics
occurred during the Archean
– However, there were probably significant
differences between Archean and modern
– Small cratons were present in the Archean
and grew by accretion along their margins.
– By the end of the Archean, 30-40% of present
volume of continental crust had formed.
What is the difference between Archean and modern plate tectonics?
• More radiogenic and residual heat from the Earth's origin would have caused the plates to move faster and magmas to form more rapidly during the
• As a result, continental accretion occurred, where
continents rapidly grew along their margins.
• Komatiite (ultramafic) lavas during the Archean.
• Little evidence of passive continental margins in
• Deformation belts indicate colliding Archean
• Archean ophiolites are rare
Explain the Plate tectonic model for the Archean crustal evolution of the southern Superior craton of
• The model shows the evolution of greenstone
belts, plutonism, and deformation.
• This model generally applies to the evolution of
other Archean crusts
Describe the difference between the modern atmosphere and the early atmosphere
– Modern atmosphere: 78% N2 and 21% O2
- Early atmosphere
• Hydrogen and helium rapidly lost to space.
• Once the core developed and a magnetic field
formed around the Earth, volcanic gases could
accumulate to produce an atmosphere without
gases being blown into space by the solar wind.
• Early atmosphere lacked O2 and was probably rich
in carbon dioxide (CO2), ammonia (NH3), and
– Evidence that it was O2-deficient and CO2-
• Detrital pyrite and uraninite (UO2) deposits, which
would have rapidly oxidized and decomposed in
the presence of O2.
– At the end of the Archean, about 2.5 bya, the
atmosphere probably had about 1% of the O2
level of today.
– O2 becomes more common in the Proterozoic.
What are the two sources of oxygen in the atmosphere?
– Photochemical dissociation
• Ultraviolet radiation from the Sun breaks down
water molecules into O2 and hydrogen.
• Could provide about 2% of Earth's current O2.
• Oxygen contributes to an ozone layer than screens
out ultraviolet radiation and protects life.
• Certain organisms use CO2 and water and expel
O2 as a waste product
What are sources of the Earth's surface waters?
1. Outgassing of Earth's interior
2. Extraterrestrial: Meteorites and icy comets
– It is not known which source was more
– Oceans existed in the Archean, but their
volumes and extent are unknown.
– The early oceans were probably also salty
and reached chemical equilibrium
What are the earliest evidence of life on earth?
Oldest fossils about 3.5 bya and chemical evidence of life in 3.8 bya rocks.
• Only monera known to
exist 3.0 bya
What is abiogenesis?
origin of life from non-living
• Life, such as a bacterium, or even a
complex organic molecule did not form
fully developed from non-living materials.
• Abiogenesis involved many small steps
What is life?
– Biologists use several criteria to define life.
– At minimum, a life form must have some sort of
metabolism (chemical activity) to maintain itself
and must reproduce.
– Sometimes distinguishing life from non-life is not
easy (e.g., viruses and microspheres).
– Abiogenesis probably involved stages where
entities resembled viruses and microspheres and
could not be clearly classified as living or nonliving.
What is the origin of life?
BESIDES GOD IN MY OPINION
The Earth's atmosphere provided CO2, water, N2, and probably ammonia (NH3) and methane (CH4).
– Lightning and ultraviolet radiation were two possible sources of energy that could have converted these chemicals into organic
molecules, monomers, which would have included amino acids.
– Monomers are the building blocks of life
– In the 1950s, laboratory experiments by Stanley Miller demonstrated that circulating
gases approximating the Earth's early atmosphere and a spark simulating lightning
could produce amino acids.
– More recent experiments using different gases have synthesized many of the 20
amino acids found in organisms.
- Monomers can polymerize into polymers, which include small molecules called thermal proteins or protobionts. Protobionts have
some characteristics of life.
– In some laboratory experiments, proteinoids
have spontaneously aggregated into microspheres, which have a protective celllike outer covering and grow and divide somewhat like bacteria
How was DNA formed?
– Modern organisms rely on DNA or RNA for reproduction.
– Many mysteries remain on how RNA and DNA developed on the early Earth.
– Researchers agree on some of the basic requirements for the origin of life, but the exact steps that were involved and the
significance of some experimental results are
What is the significance of hydrothermal vents to the origins of life?
– Submarine hydrothermal vents are located on the
ocean floor in divergent zones.
– Because the Earth had more radiogenic heat
during its early history, submarine hydrothermal
vents were probably more common than today
– Submarine hydrothermal vents precipitate copper, zinc, and iron minerals.
– They may also have produced the first elfreplicating
– The vents would have had carbon, nitrogen, sulfur, phosphorous and other elements necessarily for life and a hydrothermal energy
– Polymerization could have occurred on the surfaces of clay minerals.
– Amino acids have been detected in some hydrothermal vent emissions.
– However, some scientists are skeptical of polymerization and abiogenesis in
What are the oldest known organisms?
– First known organisms were bacteria and
– Both bacteria and archaea consist of prokaryotic cells; that is, cells that lack an
internal, membrane-bounded nucleus and
other structures typical of eukaryotic cells
– Archaea, unlike bacteria, can live in very hot, acidic, and saline environments
What are the oldest known organisms?
– Some of the oldest known fossils are stromatolites, which represent reefs
constructed by microorganisms.
– Modern stromatolites form and grow as sediment grains are trapped on sticky mats of
photosynthesizing cyanobacteria (blue-green
– The oldest known stromatolites are 3.0 bya
and are in South Africa. They may also occur in 3.3-3.5 bya rocks in Australia
- No known fossils exist of the microorganisms
that formed the Archean stromatolites.
– They must have been anaerobic, surviving without O2.
– They were prokaryotic cells
- They must have been heterotrophic, depending on an external source of nutrients, rather than autotrophic and relying on
– Their nutrient source was most likely adenosine triphosphate (ATP), which could have easily formed in early Earth environments from simple gases and