First: Pop Quiz!!1. What is my favorite element? Why?

2. 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?

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Development of Life(continued)

Stephen Eikenberry

07 September 2010

AST 2037

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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 3

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 4

Permian Era

• Land has insects, amphibians, reptiles• Reptiles could reach sizes of 10-20 feet (!)

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Permian Era: Pangaea• One of several supercontinents formed over the history of

Earth

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End-Permian• 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 (!)

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Permian Extinction• 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 ???

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Mesozoic Era• Defined to begin post-

Permian Extinction• Includes Triassic, Jurassic,

Cretaceous

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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.

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Mesozoic Dinosaurs

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Mesozoic Angiosperms

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Mesozoic Mammals

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Mesozoic Reptiles

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

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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 …

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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

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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

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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?

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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

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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

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

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

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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?)

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

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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 50-100 years

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