1. HISTORY OF LIFE ON EARTH
Physical conditions - last 4 billion years
major changes:
oxygen in atmosphere
climate change
ocean currents
sea level changes
continent movement
volcanism
meteorites

3. How do we know ages? Relative ages of rock layers (sedimentary):
their relative positions
their embedded fossils

4. Absolute ages: radioisotopes
How do we know ages?
Absolute ages: radioisotopes
carbon 14 - half life of 5,700 y.
less than 50,000 years
potassium 40 - half life of 1.3 b.y.
the most ancient events

5. AGE DIVISIONS Cenozoic: 65 m.y.a. to present Mesozoic: ~250-65 m.y.a.
Earth’s geological history is divided into eras (eg. Cenozoic) and periods (eg. Cretaceous).
boundaries between units based on differences between their fossil biotas
Cenozoic: 65 m.y.a. to present
Mesozoic: ~ m.y.a.
Paleozoic: ~ m.y.a.
Precambrian: ~550 m.y.a. to 4.5 b.y.a.

7. Crust movement
Continental drift: Throughout Earth’s history the continents have shifted, sometimes separating, at other times colliding.
Powered by radioactive decay within the Earth!

12. Climate change (temperature)
volcanism
sea level changes
ocean currents
carbon dioxide levels
......dramatic effects on the evolution of life

13. Sea level
changes...
up to 200 meters
difference

14. Meteorite collisions also have changed conditions on Earth.
cause of abrupt mass extinction at the end of the Cretaceous period (65 m.y.a)
-- iridium
-- Yucatan crater (180 km diameter)

15. Crater - in Yucutan Mexico
Meterorite or asteroid 10 miles in diameter
70% of living species wiped out
Debris blown into air caused dramatic cooling- nuclear winter
Global firestorm from methane gas released from ocean

16. The Fossil Record
Importance: Much of what we know about the history of life on Earth comes from the study of fossils.

17. Reveals broad patterns in the evolution of life.
The Fossil Record
Reveals broad patterns in the evolution of life.
Fossils show that many evolutionary changes are gradual.
Incomplete but getting better...

18. The Fossil Record

19. The Fossil Record

20. The Fossil Record

21. Life in the Remote Past Ediacara Hills
The fossil record for Precambrian times is fragmentary, but fossils from Australia show that many animals that evolved disappeared forever.
Ediacara Hills

22. Life in the Remote Past Burgess Shales
Diversity exploded during the Cambrian period. The Cambrian Explosion. Why?
All modern phyla present
... and more
chinese fossil beds +
Burgess Shales

23. Life in the Remote Past Hallucigenia
A phylum body plan that disappeared?

24. Rates of Evolutionary Change
Gradualism
Punctuated equilibrium
None? Coelacanth
... more later
– molecular clock

25. Rates of Evolutionary Change
Mass extinctions (5 so far)
99% spp. have become extinct, some during mass extinctions
major changes in flora and fauna
subsequent radiations after extinctions eg. Cenozoic radiations of modern mammals

26. Patterns of Evolutionary Change
Cambrian - all major Animal body plans (phyla) have evolved!

27. The Future of Evolution
The forces of evolution continue to operate today
eg. in humans:
West Nile Virus,
sexually transmitted diseases....

28. The Future of Evolution
Human intervention now plays an unprecedented role in the history of life.
Biodiversity crisis - the sixth great extinction