1. Geologic Time Don’t blink, you might miss it

2. The Age of the Earth Essential Question – How do we know how old the Earth is? Relative Dating Radioactive Dating Cosmological Dating Relative Dating – Using Sedimentary Rocks We know how they form = Deposition – The Law of Superposition – Rocks on bottom are older than rocks on top

3. The Age of the Earth Radioactive Dating – Remember Isotopes? » Atoms of the same element with different amount of neutrons » Carbon -14, Carbon -13, Carbon -12 Number = Atomic Mass – Some isotopes are unstable – Half-life = the amount of time necessary for one half of a radioactive isotopes to decay to its stable isotope – Decay into daughter isotopes which are stable – Very precise rate of decay » Uranium - 238 decays to Lead – 206 = 4.5 billion years » Uranium – 235 decays to Lead – 207 = 713 million years Find a rock sample – Count the amount of Radioactive isotope – Count the amount of Daughter stable isotopes – Find out how old the rock is

5. The Age of the Earth Cosmological Dating – Cosmologists observe the stars Galaxies moving away Mathematical gymnastics – Accurately measure speed – Calculate how long they have been moving away The Final Numbers Universe – 13.75 billion years old Solar System/Earth – 4.5 billion years old

6. Earth’s Timeline

7. Just a moment for “Just a Theory” http://www.pbs.org/wgbh/evolution/educato rs/teachstuds/svideos.html http://www.pbs.org/wgbh/evolution/educato rs/teachstuds/svideos.html

8. Earth’s Timeline

9. Earth’s Eras Million years ago (mya) The Precambrian = 88% of Earth’s History 4,600-540 mya – 4 billion years of single celled organisms Bacteria, Viruses, Algae, Protists Reproducing Exploiting new environments Changing the environments too! – Using Sulfur as “food” – Producing Oxygen as waste Evolving – Exploiting those new environments

10. Earth’s Eras The Paleozoic “The Cambrian Explosion” 540-250 mya – The first multi-cellular life emerges And takes off!!!!! Still very mysterious as to why it happened so fast and so sudden – 500 mya “Age of Invertebrates” – 400 mya “Age of Fishes” 1 st Land Plants 1 st Insects – 300 mya “Age of Amphibians” 1 st Reptiles

11. Earth’s Eras Mesozoic = 248-65 mya – “Age of the Reptiles” – Dinosaurs – First birds – First small mammals – First Flowering Plants Cenozoic = 65 mya-present – “Age of Mammals”