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History of the Earth.

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Presentation on theme: "History of the Earth."— Presentation transcript:

1 History of the Earth

2 History of the Earth Earth is believed to be about 5 billion years old
Little available atmospheric oxygen at this time First life on earth is believed to have been 3.9ish billion years ago – in oceans

3 What’s the evidence for this?
Paleontologists: scientists, “detectives” of the past FOSSILS! Trace Casts Petrified Imprints Amber-preserved/frozen Molds

4 How Are Fossils Formed? Most dead organisms don’t fossilize because of bacterial and fungal activity Organism falls into river Rushing water covers the dead body with sediment; minerals move into the body Time passes and more sediment compresses; minerals replace bone Earth movements reveal fossil millions of years later

5 Where Are Fossils Found?
Sedimentary rock forms layers compressing older dead, decaying organisms.

6 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

7 Geologic Time Scale 4 basic Eras Periods are time frames within eras
Major life forms dictate periods

8 Stromatolites: mats formed by cyanobacteria.
Precambrian 3.5 billion yrs ago 87% of earth’s history Major life: only prokaryotes at first then 1.8 billion yrs ago, eukaryotes appeared Stromatolites: mats formed by cyanobacteria.

9 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

10 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

11 Mesozoic Continental Drift Pangaea = one large continent
135 million years ago two large land masses: Laurasia & Gondwana 66 million years ago – most of the continents had broken apart **this affects organism distribution

12 Cenozoic 66 million yrs ago Mammals thrive
Primates appear (30 million yrs ago) Humans – 200,000 years ago

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