LECTURE 4 Flashcards
(18 cards)
archbishop james usher (1625)
- worked backwards through religious scripture
- thought earth was created on october 23rd 4004BC
uniformitarianists (1700s)
“the present is the key to the past”
- measured rate of current processes to see how long the crust would’ve taken to form
- thought million of years
lord kevin (1866)
calculated rate of cooling from a molten body the size of the earth
- thought 20-40 million years
age of earth
4.55 billion
things dated using radioactive half-lives
oldest rock = 4.04 Ga
oldest mineral = 4.39 Ga
older meteorite = 4.55 Ga
age of moon = 4.5 Ga
oldest known material = 7 Ga
geological time scale
- usually broken down by extinction events
cambrian explosion
lots of new creatures reached critical mass for evolution
- out compete each other
- cambrian arms race
biosphere
- thin layer of life on earths surface
- closed system (+ sunlight and heat)
- composed of ecosystems
- very interconnected
cambrian ocean (542-488Ma)
radiodonts = up to 1m long (first predator)
trilobites = crawl on ocean floor
pikaia = first to have a backbone - all evolved from this
opabinia
ordovician ocean (450 Ma)
nautiloids
brachipods
trilobites
graptolites
conodonts
cretaceous ocean (130 Ma)
plesiosaurs
mosasaur
ammonites
stratigraphy
study of layers of rock
biostratigraphy
part of the stratigraphy that identifies the relative ages of rock layers using fossils
- passage of time recorded in rocks
james hutton (late 1700s)
principle of uniformitarianism
“the present is the key to the past”
- same natural laws and processes that operate in the universe now have always operated in the universe and apply everywhere in the universe
nicolas steno (1669)
the principles of stratigraphy
- principle of superposition
- the top layer is the youngest
- in layered strata (sedimentary rocks and lava flows) - principle of original horizontality
- tilted/folded = originally flat
- compression buckles jt - principle of lateral continuity
- if it’s split, it’s probably on the other side too - principle of cross-cutting relationships
- if it cuts through then it’s younger
- a fault must be younger than what it cuts though
- unconformities = a period of non-deposition or active erosion
george cuvier (early 1800s)
concept of extinction
established that african elephants, indian elephants and mammoths were different species
- mammoths were once living and now extinct
william smith (1799)
principle of faunal succession
fossils succeed each other vertically
- reliable order which can be identified over wide horizontal distances
- fossils in the rock show age of the rock
- but the species has to evolve through time to show change
ideal species (index fossils)
provide information
- best if they’re alive for a short period
- more accurate when the rock was formed
four important things:
- short range
- higher resolution of age
- eg ammonites (251-66Ma) a commonly used fossil from the mesozoic (evolved rapidly) - common
- need to be able to find them to correlate them
- wide geographical distribution
- died in environments where fossilisation and preservation is likely
- glacier = too much movement for preservation
- under water = preserved = mud covers it - radiation of new species
- rapid diversification into many new forms/species after a mass extinction
- ME makes new resources available, creates new challenges, new environmental niches
- occurs at base of new geological time periods/groups of periods
- use appearance of new species to define a new period (eg at the K/Pg boundary) - background extinction
- always some species becoming extinct (background extinction)
- since last ice age:
• mammoth
• saber-tooth tiger
• cave bear
• dodo
