1. First: Pop Quiz!! What is my favorite element? Why?
What was Earth’s original atmosphere made of? What important molecule in the current atmosphere was almost completely missing? What do we think caused it to appear later on?

2. Development of Life (continued)
Stephen Eikenberry
07 September 2010
AST 2037

3. Evolutionary Timeline
530 MYa – first footprint fossil found on land
505 Mya – first true fish in the sea
475 MYa – first land plant fossils
360 MYa -- Beginning of the Carboniferous Age (lots of land plants and trees!)
360 MYa – First amphibians, followed quickly by first reptiles; insects on land/air; sharks in the ocean

4. Permian Era 285 MYa to about 250 MYa
Earth would now have been “recognizable” (if somewhat weird!)
Land has immense forests of trees and other plants (but no flowers!)
Ocean has lots of fish (including sharks), marine mammals, still trilobites too

5. Permian Era Land has insects, amphibians, reptiles
Reptiles could reach sizes of feet (!)

6. Permian Era: Pangaea
One of several supercontinents formed over the history of Earth

7. End-Permian Then … it all stopped (!)
By the late Permian, things seem to be going very well!
Tremendous diversity of life:
Plants and animals
Sea and Land
Then … it all stopped (!)

8. Permian Extinction 96% of all marine species extinct
AKA “The Great Dying”
96% of all marine species extinct
70% of land vertebrates extinct
Note – not individual critters, but entire species!
Overall mortality of living creatures even for “survivor” species might have been >95-99% (!)
“Fungal spike”:
Large jump in fungal fossils after this
Why? lots of dead plant/animal matter!
What caused it ???

9. Mesozoic Era Defined to begin post-Permian Extinction
Includes Triassic, Jurassic, Cretaceous

10. Mesozoic Era
Big “bounce” in the development of life after the Permian Extinction
Big developments:
Dinosaurs (which come to dominate)
Flowering plants (angiosperms)
Marine reptiles
Flying reptiles
First Mammals
Etc.

11. Mesozoic Dinosaurs

12. Mesozoic Angiosperms

13. Mesozoic Mammals

14. Mesozoic Reptiles

15. Late Cretaceous Again, unprecedented diversity of life on land and sea
Then (again!) it all ends!
The Cretaceous-Tertiary (K-T) extinction

16. K-T Boundary Clear geologic signature “break” found worldwide
Thin, whitish line in the rock
Interestingly, lots of dinosaurs BELOW the line; none ABOVE the line (!!)
Many other species also disappear then (pteranodons; many marine reptiles)
About 65 Mya …

17. K-T Extinction Species extincted included:
Almost ALL large vertebrates on land (dinosaurs, etc.)
Most species of plankton and reef-dwelling animals
Tropical marine invertebrates
Many land plant species
Again … these are entire species lost! Death toll for individual living beings >90% in many cases
The greatest loss of species in the last 100 million years on Earth

18. K-T: What caused it? Iridium: Rarely found on Earth’s surface
Large concentrations in the K-T Boundary worldwide
Found in similar concentration ins METEORS
Alvarez & Alvarez developed the KT Impact Theory based on this
Initially, many people skeptical
But … shocked quartz also found worldwide in K-T Boundary

19. K-T: How did that kill everything?
Energetics:
A meteor about 30 meters across has the energy of a large hydrogen fusion weapon
A small asteroid a few miles across would hit with more energy than 1,000 times the world’s entire nuclear arsenal (going off at one time in one place!)
But … even that wouldn’t kill critters worldwide, would it?

20. K-T: Impact Climate Change
That large of an impact would have sent literally tons of dust into the atmosphere
We used to worry about “nuclear winter” – this would be MUCH larger, colder, longer
Subsequent freezing of food sources and death of many photosynthetic organisms would kill/starve higher animals as well

21. K-T Impact: Chicxulub! Site just north of Yucatan peninsula in Mexico
Evidence of large impact crater
Crater age matches K-T
Crater size matches K-T energetics

22. Mass Extinctions We have seen the K-T and Permian extinctions
Evidence for several others

23. Impacts: How often? Depends on the size:
1-ton bomb – EVERYDAY! (Why don’t we notice it?)

24. Impacts: Tunguska Atomic bomb size – every 100-200 years (TUNGUSKA)
Shattered windows in Moscow (2000 miles away)
Heard on the streets of London (3000 miles away)
Flattened a forest of trees
No crater; center trees still standing; suggests “airburst” (possibly comet?)

25. Impacts: Future? Atomic bomb size – every 100-200 years (TUNGUSKA)
Extinction-level hit – every ~ MY
Aren’t we about due??

27. Later evolution Tertiary – age of mammals Human evolution timeline
Note: agriculture and human settlements about 13,000 years ago
Writing, etc. about 5,000 years ago or so
Pyramids and Ziggurats
Transport via boats, etc.
Telecommunication
Space travel
Most signs of “intelligence” limited to the past years