Learning Obj. Lecture 7 (extinction events)

Geological timelines

Bif formations - 3.8 BYA

Extinction causes

• Major asteroid impacts

• Volcanic eruptions

Major cosmic collision

Chicxulub (66mya)

• 110 km crater

• 10 km bolide

5 Major extinction events

• 66 mya - End-cretaceous event (K-T boundary) [Chicxulub asteroid]

• 206 mya - End-triassic event [80% species extinct, dinosaurs diversify]

• 255 mya - End-permian event [90% species extinct]

• 363 mya - End-devonian event [40% marine life died]

• 455 mya - End-ordovician event [85% marine species]

Reason for Antrhopocene

Anthropo- humans

• Time when humans became dominant life-forms

6 Fossil types

• Compression

• Molds & Casts

• Impressions

• Permineralizations

• Unaltered material

• Chemical fossils

Index Fossils

• relative dating

• Good ones have wide-geographic distribution

• Persisted for short geological periods

• Easily diagnosed and identified

Absolute dating

• Radioactive isotopes decay at constant rate

  • each has ½ life

• Ratio of parent to daughter isotopes change over time

  • More daughter product = older sample

Half-life of Carbon-14

5,730 years

• Dates 50,000 - 60,000 years old

• C-14 : C-12

• N-14 daughter isotope

Uranium-238

• Millions to billions of years

• daughter product Lead-206

• 4.47 billion year ½ life