2History of the Earth Earth is believed to be about 5 billion years old Little available atmospheric oxygen at this timeFirst life on earth is believed to have been 3.9ish billion years ago – in oceans
3What’s the evidence for this? Paleontologists: scientists, “detectives” of the pastFOSSILS!TraceCastsPetrifiedImprintsAmber-preserved/frozenMolds
4How Are Fossils Formed?Most dead organisms don’t fossilize because of bacterial and fungal activityOrganism falls into riverRushing water covers the dead body with sediment; minerals move into the bodyTime passes and more sediment compresses; minerals replace boneEarth movements reveal fossil millions of years later
5Where Are Fossils Found? Sedimentary rock forms layers compressing older dead, decaying organisms.
6Fossil Dating Relative Dating Determined by layers of rock above fossilGeological LAWDepicts order of appearance and/or extinction of organismsAge is only in relation of other fossilsRadiometric DatingHelps determine SPECIFIC ageAmount of radioactive isotope decay (half-life)Potassium-40 = half-life of 1.3 billion yrsCarbon-14 = half-life 5730 yearsOften inconsistent
7Geologic Time Scale 4 basic Eras Periods are time frames within eras Major life forms dictate periods
8Stromatolites: mats formed by cyanobacteria. Precambrian3.5 billion yrs ago87% of earth’s historyMajor life: only prokaryotes at first then 1.8 billion yrs ago, eukaryotes appearedStromatolites: mats formed by cyanobacteria.
9Paleozoic 245 million years ago Cambrian period brought biodiversity Fish then amphibians then reptiles (oh my!)Mass extinction knocked out 90% of marine and 70% of land biodiversityPlate-skinned fish
10Mesozoic 245 million yrs ago Jurassic period = “the age of the dinosaur”Fossil evidence shows that modern birds evolved from dinosaursNew kinds of mammals and flowering plantsCretaceous Period ended with another mass extinction 66 million yrs ago (meteorite collision!)Yanoconodon: fossil shows evidence of evolution from reptilian jaws and ears to mammalian
11Mesozoic Continental Drift Pangaea = one large continent 135 million years ago two large land masses: Laurasia & Gondwana66 million years ago – most of the continents had broken apart**this affects organism distribution
12Cenozoic 66 million yrs ago Mammals thrive Primates appear (30 million yrs ago)Humans – 200,000 years ago