people in stratigraphy
steno: suggested deeper layers of rock are older
hutton: uniformitarianism ~ theory that changes in earth’s crust come from universal & uniform processes
cuvier: established different species
stages of geological time
precambrian v phanerozoic
paleozoic, mesozoic, cenozoic
index fossils
can use to tell what era a rock is from, fossils with a short timeline of existence work best
criteria for mass extinction
30% of species extinct
broad range of ecosystems affected
5 extinctions
ordovician (450Ma) ~ ice age
devonian (375-360Ma) ~ drastic drop in
oxi levels
permian (252Ma) ~ volcanism, impacts
triassic (200Ma) ~ eruptions, asteroids
cretaceous (65Ma) ~ chicxulub impact, deccan traps
generic causes of extinctions
biological changes
impacts
climate change
plate tectonics
end-permian extinction
- closest life has come to failing completely
- pangaea caused lack of biodiversity, oceans stagnated, possible impacts, siberian traps led to global warming
- allowed dinosaurs to evolve
end-triassic extinction
- caused by volcanism, climate change, possible impacts
- allowed dinosaurs to take over
cretaceous/paleogene extinction
- caused by chicxulub impact & deccan traps
- wiped out dinosaurs completely
- impact led to forest fires (warming), then an impact winter (cooling), then release of methane gas (warming)
evidence for chicxulub impact
- alvarez hypothesis: iridium anomaly
- fern spores and soot layers evidence of global fires
- tanis fossil site
raup & sepkoski’s hypothesis
25 myr cycle in impacts
asteroid mitigation strategies
ablation (vaporising)
DART (redirecting)
fragmentation
orbit adjustment
all v expensive and require much notice
