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?

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

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

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

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

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

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 (!)

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 ???

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

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.

Mesozoic Dinosaurs

Mesozoic Angiosperms

Mesozoic Mammals

Mesozoic Reptiles

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

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 …

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

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

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?

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

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

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

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

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?)

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

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