Presentation on theme: "History of the Earth. 5 billionEarth is believed to be about 5 billion years old Little available atmospheric oxygen at this time 3.9ish billionFirst."— Presentation transcript:
History of the Earth
5 billionEarth is believed to be about 5 billion years old Little available atmospheric oxygen at this time 3.9ish billionFirst life on earth is believed to have been 3.9ish billion years ago – in oceans
Whats the evidence for this? Paleontologists: scientists, detectives of the pastPaleontologists: scientists, detectives of the past FOSSILS!FOSSILS! –Trace –Casts –Petrified –Imprints –Amber-preserved/frozen –Molds
How Are Fossils Formed? Most dead organisms dont fossilize because of bacterial and fungal activity 1.Organism falls into river 2.Rushing water covers the dead body with sediment; minerals move into the body 3.Time passes and more sediment compresses; minerals replace bone 4.Earth movements reveal fossil millions of years later
Where Are Fossils Found? Sedimentary rock forms layers compressing older dead, decaying organisms.
Fossil Dating Relative Dating Determined by layers of rock above fossil Geological LAW Depicts order of appearance and/or extinction of organisms Age is only in relation of other fossils Radiometric Dating Helps determine SPECIFIC age Amount of radioactive isotope decay (half-life) Potassium-40 = half-life of 1.3 billion yrs Carbon-14 = half-life 5730 years Often inconsistent
Geologic Time Scale 4 basic Eras4 basic Eras Periods are time frames within erasPeriods are time frames within eras Major life forms dictate periodsMajor life forms dictate periods
Precambrian 3.5 billion yrs ago 87% of earths history Major life: only prokaryotes at first then 1.8 billion yrs ago, eukaryotes appeared Stromatolites: mats formed by cyanobacteria.
Paleozoic 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 biodiversity Plate-skinned fish
Mesozoic 245 million yrs ago Jurassic period = the age of the dinosaur Fossil evidence shows that modern birds evolved from dinosaurs New kinds of mammals and flowering plants Cretaceous 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
Mesozoic Continental Drift 1.Pangaea = one large continent million years ago two large land masses: Laurasia & Gondwana 3.66 million years ago – most of the continents had broken apart **this affects organism distribution
Cenozoic 66 million yrs ago Mammals thrive Primates appear (30 million yrs ago) Humans – 200,000 years ago