Lecture 7 Geological timeline, extinction events, fossils

give some details about geological timeline

defines major geological and biological events

Divided into eons, eras, periods and epochs where eras are mostly divided by extinction events.

Fossils of various clades give structure for timeline.

Give info on extinction events. How often do they occur. When was most recent

Occur on small and large scales

Volcanic eruptions or smaller scale impacts with asteroids.

Occur every 10-100 mil years

Most recent was 65 mya at end of cretaceous

Major extinction events

66 mya: End Cretaceous (asteroid)

206 mya: End Triassic (climate)

255 mya: End Permian (increase CO2 to 2500 ppm) caused 90% extinction. Took 20 mil years

363 mya: End Devonian (Climate/asteroid) 40% marine life lost

455 mya: End Ordovician (climate) 85% marine life

What is a fossil

any evidence of life before written documents

What are fossils important for

Reconstruct old ecosystems, studying biogeography, and biostatigraphy with index fossils used for dating

Two ways of inferring ages of fossils and rocks

Absolute dating: measures how carbon 14 (trace amounts) decays to N14 over a half life of 5730 years. Only works for younger things like 50-60k years

Relative dating: Dates the decay of U 238 to PB 206 over 4.5 billion years half life.