Evolution9/10/14Darwin recognized that evolution required an old earth:- Darwin argued that the earth was billions of years old. This was going against Lord Kelvin’s theory of the Earth’s age, which he predicted to be only 20 million years oldRadioactive Decay:- Half life- amount of time it takes for half the atoms to give off radiation and decayo Different isotopes have different half-liveso Uses radiodating to date fossilsPlate Tectonics:- Continetial Drift: new crust is being formed and old crust is being pushed into subduction zone.o In the last 400 million years continental drifts have been drasticBig Bang- 16 billion years agoEarth formed- 4.5 billion years agoOldest terrestrial rocks- 38 billion years agoAbundant life- 3.5 billion years agoOxygen present in the atmosphere- 2.5 billion years agoFossil record shows that earlier organisms evolved into later organisms- Vast majority of species are extinct- Numbers of species increase over time- Earlier organisms were smaller and more simpleFossils allow us to learn about extinct species- Most organisms don’t fossilize o Occasionally soft tissue fossilize Burgess Shale (505 mya) - 65000 specimens, 93 species- Fossils can provide clues of developmento Head/body size over time, morphologists take interest in thiso Scanning electron microscopy provides evidence of cell structureo Cat scans help determine function of hadrosaur crest Crest connected to naval cavity- sound generated by blowing air, ears tuned to frequencyo Biomarkers reveal traces of life Biomarker: distinctive molecules only produced through biological activity- Earliest life unlikely to be preserved in fossilso Oldest evidence dates back to 3.7 bya Carbon in rocks (controversial) How do early organisms fit into the tree of life?- There are three basic groups we can group organisms in: bacteria, archea and archaeao It’s controversial to place some old organisms in these categories because it’s hard to judgeo Bacteria was formed about 2.6 byaEvolution9/10/14Origin of multicellular organisms was a major transition in history of lifeEukaryotic multicellular life dates algae at 1.6 byaThe Dawn of animals:- Earliest animal we have evidence of was the sponge. Oldest fossils date back to 650 mya- Search of early animals can be controversialo Animal embryos or animal relatives?- Ediacaran fauna- diverse/unique animals dominated the oceans (575-535 mya)o Many hard to place taxonomically - Currently existing lineages recognizable during the early Cambrian o Cambrian explosion (542 mya) - Chordates emerged in early Cambrian time- [Halkoulchthys- lead to fish]Transition from sea to land:- Prokaryotes colonized terrestrial environmentso Fossils date to 2.6 mya- First plant and fungal life have fossils dating 475 mya - First invertebrates date back to 480 myao Probably relatives to today’s insects and spiders- 428 mya is the oldest fully terrestrial animal found in the fossil recordsFamiliar life didn’t form until about 350 mya- Evolution of mammals- (evolved from synapsids) was about 150 mya- Diversification of mammals- mammals diversified after dinosaurs (65 mya)Major lineages: -Birds: 150 mya (descendants of dinosaurs)-Plants: 132 mya-Insects: 400 mya- current lineages appear