Midterm 1 Flashcards

Question

Describe the carbonate group of minerals

Answer 1

–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.

Answer 2

–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.

Answer 3

* Uplift and exposure of rocks * Weathering of rocks to sediments * Sediment transport and deposition * Burial of sediments and lithification * Metamorphism * Melting to form magma * Crystallization of magma * Consolidation * Volcanic eruptions

Answer 4

* Uplift and exposure of rocks * Weathering of rocks to sediments * Sediment transport and deposition * Burial of sediments and lithification * Metamorphism * Melting to form magma * Crystallization of magma * Consolidation * Volcanic eruptions

Answer 5

–Gravel (>2 mm) –Sand (1/16-2 mm) –Silt (1/256 - 1/16 mm) –Clay (<1/256 mm), Mud is silt and/or clay.

Answer 6

``` –Running water - most effective –Glaciers –Wind –Waves ```

Answer 7

–Steam channels –Beaches –Seafloors, etc.

Answer 8

–Conversion of unconsolidated sediment to sedimentary rock –Burial of sediments –Compaction - pressure from burial

Answer 9

1. detrital clastic 2. detrital sedimentary rocks 3. chemical sedimentary rocks

Answer 10

• 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).

Answer 11

• 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.

Answer 12

• 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 seawater

Answer 13

1. Compaction - packing sediment grains through burial - reduces volume by 40% - involves desiccation which is the loss of water from pore spaces resulting from compaction/evaporation 2. Cementation - minerals precipitate from sediment pore fluids to bind together grains - most common cements = calcite and quartz

Answer 14

- 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

Answer 15

- 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)

Answer 16

- ultramafic - mafic (ferromagnesian minerals dominant) - intermediate - felsic (nonferromagnesum minerals dominant)

Answer 17

- 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) - obsidian - pumice - vesicular volcanic glass - scoria - vesicular, less glassy than pumice

Answer 18

- 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

Answer 19

- heat (plutons and lava flows, deep burial) - pressure (deep burial and differential pressure - fluid activity (water and other liquids and gases)

Answer 20

- contact metamorphism (plutons) - regional metamorphism (plate boundaries continent-continent; oceanic- continent) - dynamic metamorphism (rocks adjacent to faults)

Answer 21

- foliated (pressure causes platy and elongated minerals to align) - non-foliated (low pressure contact metamorphci rocks; rocks without platy or elongated minerals)

Answer 22

- slate - phyllite - schist - gneiss - amphibolite - migmatite

Answer 23

- marble - quartz - greenstone - hornfels - anthracite

Answer 24

- Earth's heat contributes to melting and metamorphism. • Plate tectonics responsible for rock cycle. • Sediment along continental margins buried and lithified. • Convergent plate boundaries result in mountain building, metamorphism and igneous activity. • Mountains erode and produce sediments.

Answer 25

``` – They preserve evidence of ancient surface processes of their depositional environments, such as running water and glaciations. – Most fossils occur in them, which tell us about the history and evolution of life. Fossils are also important in relative dating. - They contain valuable resources, such as: oil and natural gas, coal, sand and gravel, gypsum, quartz, phosphate, banded iron formation ```

Answer 26

- textures - measuring thickness and lateral extent - noting the composition and any fossils - recording relationships with other rocks

Answer 27

microscopic examinations, fossil identification, and chemical analyses.

Answer 28

``` to interpret the depositional environments of sedimentary rocks. Modern depositional environments often provide important insights into ancient environments. ```

Answer 29

Texture refers to the size, size distribution, shape and arrangement of clasts in detrital sedimentary rocks. – Grain size in detrital rocks provides information on transport conditions and deposition. – The transport of gravels requires glaciers or rapidly flowing water. – Muds are deposited in low-energy environments.

Answer 30

– 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 transport. – Sand grains round with considerable transport. – Muds that are suspended in water are usually not well-rounded

Answer 31

Sorting refers to the size variation of clasts in sediments or sedimentary rocks. – 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

Answer 32

``` – Larger scale features than textures. – Often form during deposition or shortly afterwards. – Important in interpreting depositional environments 1. laminations 2. beds 3. cross-bedding 4. ripple marks 5. mud cracks ```

Answer 33

Layers less than 1 cm thick are laminations. Thicker layers are beds. – Laminations are most common in mudrocks, but also occur in sandstones and limestones. – Limestones, sandstones, conglomerates may be bedded. – Bedding planes separate beds.

Answer 34

- 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.

Answer 35

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

Answer 36

``` Ripple marks are small scale alternating ridges and troughs on bedding planes, especially in sand. – 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. ```

Answer 37

– 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

Answer 38

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.

Answer 39

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

Answer 40

Deposited in stream channels and barrier islands

Answer 41

``` • Lens-shaped geometry in profile • Lobate geometry from above - Coarse sediment deposited first, close to river mouth (Foreset beds) – Silt and clay transported farther then deposited (Bottomset beds) – Horizontal beds deposited on top of foreset beds during floods (Topset beds) ```

Answer 42

– 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.

Answer 43

``` • Found in small samples, including well cuttings in petroleum exploration. • If not transported, may be good environmental indicators. • Sometimes used as guide fossils in relative dating ```

Answer 44

``` • Depositional environments are locations where sediments accumulate. • Physical, chemical and biological processes operate to yield distinctive sediments. • Three main categories: – Continental – Transitional – Marine ```

Answer 45

– 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

Answer 46

``` Deserts • Dunes: cross-bedding • Alluvial fans: stream deposits • Playa lakes: muds and evaporites • Fossils, if present, are terrestrial plants and animals ```

Answer 47

Glacial • 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

Answer 48

Deltas • 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

Answer 49

* 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

Answer 50

* 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.

Answer 51

• 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 fossils. • At the edge of the continental shelf, turbidity currents transport sediments through submarine canyons to form submarine fans on the continental slope and rise

Answer 52

• Mostly covered by pelagic clay and ooze. • Major sources of sediment include: wind-blown dust, volcanic ash and ooze (shells of microorganisms). • Mid-oceanic ridges. • Iceberg dropstones in high latitudes

Answer 53

``` –Limestones and dolostones. – Dolostones - limestones altered by magnesium fluids during diagenesis & lithification. – 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. ```

Answer 54

• Barriers, such as reefs. • Reefs include corals, mollusks and sponges. • Ooids - spherical carbonate grains that lithify to oolitic limestone. • Micrite with marine fossils and bioturbation in lagoons.

Answer 55

``` – Mostly rock salt and rock gypsum. – Some deposited in playa lakes. – Most extensive deposits form in evaporating restricted seas in arid environments ```

Answer 56

• 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 environments. • Multiple maps of an area at different times can illustrate marine transgressions and regressions.

Answer 57

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.

Answer 58

``` 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 • Unconformities • Fossils ```

Answer 59

relative dating tells us the relative sequence of events while absolute dating tells us exactly when a rock is formed

Answer 60

– 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.

Answer 61

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 relationships.

Answer 62

The Principle of Inclusions is another method to determine relative ages between rocks. • The principle states that inclusions or rock fragments within a rock are older than the host rock.

Answer 63

are surfaces of erosion and/or nondeposition within sedimentary rocks.

Answer 64

``` more or less continuous. • Unconformities are surfaces of erosion and/or nondeposition within sedimentary rocks. • Erosion and/or nondeposition may have lasted for millions of years. • A hiatus is an interval of geologic time not represented by strata ```

Answer 65

– Disconformity – Nonconformity – Angular unconformity

Answer 66

separates younger from older sedimentary strata that are parallel to each other.

Answer 67

is an erosional surface cut into igneous or metamorphic rocks and overlain by younger sedimentary rocks.

Answer 68

is an erosional surface on tilted or folded rocks, over which younger sedimentary rocks were deposited.

Answer 69

• 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.

Answer 70

– 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 environment. – Deposition in each of these laterally adjacent environments yields a sedimentary facies.

Answer 71

a body of sediment with distinctive physical, chemical, and biological attributes. – 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 facies. • 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.

Answer 72

caused when sea level falls relative to the land, results in nearshore facies overlying offshore facies.

Answer 73

– 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.

Answer 74

• 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 evolution. • Fossils also provide relative ages between separated columnar sections of rocks.

Answer 75

– Body fossils - shells, bones, teeth, and rarely soft parts. – Trace fossils - tracks, trails, burrows, nests, and dung.

Answer 76

– Favorable conditions for fossilization • Durable body parts • Lived where burial in sediment was likely • Avoided decay, scavenging and metamorphism

Answer 77

``` – Unaltered body fossils - largely retain their original structure and composition – Altered body fossils - structure and composition changed – Trace fossils – Molds and casts • Mold - an impression of an organism • Cast - minerals or sediments fill the mold, a replica of the original ```

Answer 78

– 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 order. – Because the succession of fossils in the geologic record is ordered and not random, they can be used for relative dating

Answer 79

when they first appeared and when | they became extinct

Answer 80

``` • 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 Cambrian System. • Sir Roderick Impey Murchison named the younger Silurian System in southern Wales. • 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 scale. ```

Answer 81

is defined by its rock type(s) without consideration of its age or mode of origin. – The basic lithostratigraphic unit is the formation. – A formation is a mappable body of rock with distinctive upper and lower boundaries.

Answer 82

– 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

Answer 83

– Time-stratigraphic (chonostratigraphic) unit, indicates that a particular rock unit formed during a particular time interval. – The basic time-stratigraphic unit is the system. – 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 units. – 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.

Answer 84

• 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 Succession.

Answer 85

– 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.

Answer 86

– Biozones are effective in time-stratigraphic correlation. – 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 time equivalence. • Lava flows and volcanic ash falls. Each formed rapidly at a specific time. – Precambrian rocks lack useful fossils. Radiometric dating is most useful.

Answer 87

– Useful fossils or guide fossils have the following characteristics: • Easily identified. • Geographically widespread. • Lived for brief periods of geologic time. • Atrypa and Paradoxides are good guide fossils. Lingula is not.

Answer 88

• 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 years old.

Answer 89

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

Answer 90

• 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.

Answer 91

``` - In the late 19th century, Austrian geologist Edward Suess noticed that the Late Paleozoic plant fossil, Glossopteris, was located in India, Australia, South Africa and South America. ``` - How did this fossil get distributed in these widely separated areas with very different modern climates?

Answer 92

- 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 southern landmass called Gondwana. As Pangaea broke up, the various continents moved to their present day locations

Answer 93

1. Continental fit - There are close fits between the continents, although only beyond the continental shelves at depths of about 2000 m. 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 the 1950s.

Answer 94

- 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 South pole. - 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 formation

Answer 95

is the temperature at which hot iron-bearing minerals cool enough to gain magnetism

Answer 96

- 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

Answer 97

Earth’s present magnetic field is considered "normal." - 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 magnetism ```

Answer 98

- 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 ridge

Answer 99

- 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)

Answer 100

- 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

Answer 101

- the lithosphere is divided into different plates - seven major plates and many minor ones - Some plates include continental as well as oceanic crusts. - 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 trenches.

Answer 102

Proterozoic Eon

Answer 103

1. Divergent 2. Convergent 3. Transform

Answer 104

– 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.

Answer 105

- Characteristic features of ancient continental rifting include: faulting, dikes, sills, lava flows, and thick sedimentary sequences within rift valleys. – Pillow lavas and associated deep-sea sediments are evidence of ancient spreading ridges.

Answer 106

``` - Modern example: East Africa. – Initial stages of continental breakup. – Rift valleys and volcanism. – Rift valleys expand and create seas, such as Red Sea. – As divergence continues, seas may expand into oceans and continents have passive margins. ```

Answer 107

where two plates collide

Answer 108

1. oceanic - oceanic boundary 2. oceanic - continental boundary 3. continental - continental boundary

Answer 109

- 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 occurs. – Volcanoes result from rising magma produced by the partial melting of the subducting plate. – Japan and the Aleutian Islands of Alaska

Answer 110

– 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

Answer 111

– 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 chain. – Himalayan Mountains of Asia

Answer 112

– 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 plate boundaries

Answer 113

– Plates slide laterally past each other along transform faults. – San Andreas Fault in California, USA. – Other transform faults connect oceanic ridge segments

Answer 114

– 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 Island chain

Answer 115

- 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 movement: 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

Answer 116

- 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

Answer 117

- Spreading ridges: Hot ascending limbs of cells. – Trenches: Cooled part of convention cells descend

Answer 118

- 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 trenches

Answer 119

``` episode of intense rock deformation or mountain building. • Results from the compressive forces of converging plates. • Subduction: – Folds and faults sediments and volcanic rocks. – Deeper rocks are metamorphosed. – Magmas form ```

Answer 120

• Organisms occupy biotic provinces controlled mostly by: – Climate – Geographic barriers • Plate movements create mountains and continental barriers that influence climate and biological evolution • Plate Tectonics and Biological Evolution in the Americas – Formation of Panama by plate movements about 5 million years ago isolated Caribbean and Pacific marine organisms promoting separate evolution. – North American land animals migrated to South America, causing extinctions of South American species

Answer 121

Petroleum – During the Mesozoic Era, much of the Middle East was a broad marine shelf near the equator. – Countless microorganisms lived in the warm surface waters, died and accumulated in sediments. – Burial of the organic-rich sediments from subduction created the right amount of heat to produce petroleum. – 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 boundaries. – Copper ores along the convergent boundaries of the west coasts of the Americas

Answer 122

- 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 survive

Answer 123

Darwin was convinced that organisms descend with modification from ancestors

Answer 124

• 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

Answer 125

• Biological evolution, or descend with modification from ancestors, may be small-scale: – Changing genetic makeup of populations from generation to generation. • Biological evolution may be large-scale: – Origin of a new species from a common ancestor • 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

Answer 126

``` Beginning in the 18th century, naturalists sought evidence for Genesis, but instead found evidence for evolution ```

Answer 127

``` James Hutton (uniformitarianism) and others concluded that the Earth was far older than the creation date proposed by Archbishop Ussher ```

Answer 128

``` Georges Cuvier demonstrated that many plants and animals are now extinct. How was that possible if Noah succeeded in saving them from the Genesis Flood? ```

Answer 129

– 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 offspring. – 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.

Answer 130

– 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

Answer 131

- 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 running.

Answer 132

- 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 alleles - 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 dominance

Answer 133

– Mendel was unaware of: • Mutations (changes in genetic material). • Chromosomes. • Some genes control the expression of other genes. • Hox genes, which regulate the development of major body segments.

Answer 134

- Chromosomes are complex, double- stranded helical molecules of deoxyribonucleic acid (DNA). – Chromosomes are found in the cells of all organisms.

Answer 135

– Specific segments of the DNA molecule are | hereditary units called genes

Answer 136

``` – The number of chromosomes are 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 traits. ```

Answer 137

``` Sex cells • Pollen and ovules in plants • Sperm and eggs in animals. – 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 population ```

Answer 138

Development of Neo-Darwinism in the 20th Century – 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

Answer 139

``` – Mutations - changes in chromosomes or genes. – Chromosomal mutation - affects large segment of a chromosome. – Point mutation - a change in a gene. – Point mutations in sex cells are inheritable ```

Answer 140

Mutations are random and may be harmful, beneficial, or neutral. – If a species is well adapted to its environment, most mutations would not be useful and could be harmful. • Some plants of a species develop resistance to contaminants in soils around mines, but die in uncontaminated soils. • 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

Answer 141

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

Answer 142

new species arising from an | ancestral species. Well documented

Answer 143

Species - a population of similar individuals that interbreed in nature and produce fertile offspring. This definition does not apply to asexual organisms

Answer 144

``` – 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 ancestors – 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 ```

Answer 145

* Allopatric speciation * Phyletic gradualism * Punctuated equilibrium

Answer 146

When a group is isolated from its parent population, gene flow is restricted or eliminated, and the isolated group is subjected to different selection pressures. – Causes of isolation: • Mountain barriers • Rising sea level – Disagreement over how rapidly a new species might evolve because of it

Answer 147

Gradual accumulation | of minor changes brings about a new species

Answer 148

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 biologists. – Polyploidy - Some new plant species arise by the doubling of chromosomes

Answer 149

``` 1. Isolation or partial isolation of a species is often the first step to speciation. Common in: • Mosquitoes • Bees • Mice • Salamanders • Fish • Birds ```

Answer 150

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 ancestors

Answer 151

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 environments Examples of Convergent evolution • Mammals in North and South America • Tasmanian "wolf" (marsupial) and dogs and hyenas • Sharks, ichthyosaurs (extinct marine reptiles), and dolphins.

Answer 152

organisms evolve characteristics, but still have characteristics of their ancestors.

Answer 153

– Evolution does not affect all aspects of an organism simultaneously. – 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 environments - 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

Answer 154

evolutionary history

Answer 155

• 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 random

Answer 156

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

Answer 157

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

Answer 158

- Mass extinctions are times of accelerated extinction rates and losses in Earth’s biologic diversity. – 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

Answer 159

– Classification of organisms – Embryology – Comparative anatomy – biogeography – Fossil record - biochemistry - 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 do.

Answer 160

Two-part genus and species name developed by Carolus Linnaeus (1707-1778). – Linnaeus' classification of organisms becomes more inclusive from species to kingdom. – 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 evolutionary relationships

Answer 161

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 ancestors. 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 reptiles 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

Answer 162

• 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

Answer 163

• Examples would be the ‘dewclaw’ in a dog, ‘wisdom teeth’ in a human, and the pelvis in the whale. • The human jaw is now too short to accommodate the ancestral number of teeth

Answer 164

• 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

Answer 165

Fossils show a sequence in the geologic record that is explained by evolution: – One-celled organisms appeared before multicelled organisms. – 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 support evolution 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

Answer 166

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. – Intermediates • Fish and amphibians • Mammal-like reptiles and mammals • Whales

Answer 167

4.6 billion years old (bya)

Answer 168

- 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

Answer 169

Archean and Proterozoic - Because of a lack of fossils, the divisions of the Precambrian are based on absolute dates rather than time-stratigraphic units.

Answer 170

- 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

Answer 171

- 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 in silica. • Partial melting of mafic rocks also produced more silica-rich magmas and rocks. • Subduction of crust formed small island arcs, which collided and accreted into the first proto-continents

Answer 172

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

Answer 173

* Some isotopes have unstable nuclei | * Nuclei spontaneously break apart (decay) to give off energy as particles or rays

Answer 174

``` 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 neutron ```

Answer 175

The Archean includes 32.6% of geologic | time.

Answer 176

``` because: – Most are metamorphosed and completely deformed. – Most are currently deeply buried and difficult to access. – They contain few (or no) fossils ```

Answer 177

- All continents have an ancient, stable craton made up of a Precambrian shield and platform - Cratons are the foundations or nuclei of the continents. - 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.

Answer 178

- 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 metamorphosed.

Answer 179

Platforms consist of buried Precambrian rocks.

Answer 180

– Three main rock associations: • Lower - mostly volcanic • Middle - mostly volcanic • Upper - mostly sedimentary. – Synclinal structure, 40-250 km wide, 120-180 km long. – 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 fragments. • Argillite – low-grade metamorphosed mudstones. – Other sedimentary rocks: • Sandstones, conglomerates, chert, carbonates • Banded iron formations.

Answer 181

``` – 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 ores. ```

Answer 182

– 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.

Answer 183

– Most geologists believe that plate tectonics occurred during the Archean – However, there were probably significant differences between Archean and modern plate tectonics. – 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.

Answer 184

• 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 Archean. • 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 the Archean. • Deformation belts indicate colliding Archean cratons. • Archean ophiolites are rare

Answer 185

• The model shows the evolution of greenstone belts, plutonism, and deformation. • This model generally applies to the evolution of other Archean crusts

Answer 186

– 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 methane (CH4). – Evidence that it was O2-deficient and CO2- rich: • 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.

Answer 187

– 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. – Photosynthesis • Certain organisms use CO2 and water and expel O2 as a waste product

Answer 188

1. Outgassing of Earth's interior 2. Extraterrestrial: Meteorites and icy comets – It is not known which source was more important. – Oceans existed in the Archean, but their volumes and extent are unknown. – The early oceans were probably also salty and reached chemical equilibrium

Answer 189

Oldest fossils about 3.5 bya and chemical evidence of life in 3.8 bya rocks. • Only monera known to exist 3.0 bya

Answer 190

``` origin of life from non-living matter. • 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 ```

Answer 191

– 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.

Answer 192

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

Answer 193

Not known – 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 debated.

Answer 194

– 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 molecules. – The vents would have had carbon, nitrogen, sulfur, phosphorous and other elements necessarily for life and a hydrothermal energy source. – 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 hydrothermal vents

Answer 195

– First known organisms were bacteria and archaea. – 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

Answer 196

– 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 algae). – 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 photosynthesis. – Their nutrient source was most likely adenosine triphosphate (ATP), which could have easily formed in early Earth environments from simple gases and phosphate.

Answer 197

- Later, organisms evolved to rely on fermentation as an energy source. – Fermentation is an anaerobic process, where sugars are split to release carbon dioxide, alcohol, and energy. – Most modern prokaryotic cells ferment. – Photosynthesis probably developed about 3.5 bya

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