PRELIM 1 Flashcards
Lagerstätten
storage - place
- fossil sites where there is exceptional preservation; numerous + well preserved fossils
Burgess Shale
- famous Lagerstatten from the Cambrian
Absolute dating
radioactive decay to get age:
- after 1 half-life; 50 % daughter, 50% parent
- 2 half-life: 75% daughter, 25% parent
-3 : 87.5 daughter, 12.5 parent
*can only date igneous rock b/c daughter isotope is at 0% in molten rock
Relative dating
dating a layer relative to other dates
Geological time scale
- age of earth: 4.6 bya
- 1st life: 3.7 bya
- Cambrian explosion : 540 mya
- End of paleozoic: 250 mya
- end of mesozoic/start cenozoic: 65 mya
- anthropocene: 10 kya
dates found w radioacarbon dating
Superposition
the youngest layers are the ones laying on top
Lateral continuity
layers continue laterally over distances
- each layer is deposited at the same time & is the same layer even if eroded
Original horizontality
layers are deposited horizontally and maybe be deformed later
- movement of continental plates
- layers that are vertical/non-horizontal were originally horizontal
Cross-cutting
geological layers/ intrusions that cut across other layers are younger than layers that its crossing
Index fossils
- fossils in a distinct rock layer/short lived
- geographically widespread to help identify layers in different locations
can be used for stratigraphic correlation
Carbon dating
effective range 100 - 100k
5,730 yr half-life
Uranium lead dating
- effective dating range 10 million - 4.6 billion?
K- Ar dating
half life 1.3 billion yrs
- effective for 100k - 4.6 billion years
Precambrian & phenazoic era
Phanerozoic
all of the eras starting from the cambrian on
Fossils
remains, traces, impressions of once living organisms
most fossils are found in sedimentary rocks
Conditions that impede fossilization
- predators and scavengers
- bacterial decay
- dissolution in water
- physical disturbance
Conditions that promote fossilization
- rapid burial:
- protection from physical disturbance
- anaerobic environments
sedimentary rocks
formed from deposition of sediments falling to the bottom of body of water
what gets preserved
- teeth, bone, and chitinous exoskeletons or calcium carbonate shells
- plants: seeds, pollen, leaves, wood, rarely flowers
- bacteria, microbial mats; stromatolites formed from biofilms of cyanobacteria that trap sediment
types of preservation
- skeletal + other body elements are the most informative
- per mineralization/petrification: minerals are deposited in tiny holes within bones or wood, replacing organism and making stone structure
- impression fossils: made from a carbonaceous film imprint
phylogeny
cladogram: shows branching order and topology only
phylogram: branch lengths reflect the amount of evolutionary change
chronogram: cladogram where branch lengths are calibrated to real time
monophyletic
a clade: organism and all its descendants
clade
an organism and all its descendants
- most recent common ancestor to all the taxa