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Interpreting Earth’s History

Interpreting Earth’s History. How can rocks be correlated? And Geologic Time Scale. Index Fossils. Index fossils are: commonly found widely distributed limited in time span . H elp in dating other fossils found in the same layer. Ash layers are also good time markers

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Interpreting Earth’s History

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  1. Interpreting Earth’s History How can rocks be correlated? And Geologic Time Scale

  2. Index Fossils • Index fossils are: • commonly found • widely distributed • limited in time span. • Help in dating other fossils found in the same layer. • Ash layers are also good time markers • Humans will one day make excellent index fossils

  3. Correlation • Correlation- or CO-RELATION (two or more things related) is a critical tool in the reconstruction of Earth’s history. • Geologists match similar rock strata in different locations to see if they formed at the same time or under similar conditions

  4. Who’s got the TIME?- • RELATIVE: order/sequence known, but not the actual date of occurrence. • ABSOLUTE: actual date known. If 2 dates are known, then the RATE OF CHANGE can be known- such as Mountain Building.

  5. First Things First…or…“How’d that get there?” • In the 17th C., Nicolas Steno made an important observation: • "Sediments are usually deposited in horizontal layers." This was called: “ORIGINAL HORIZONTALITY”

  6. REVIEW: • SUPERPOSITION: sedimentary sequence will be OLDEST on BOTTOM (if undisturbed). • CROSS-CUTTING:igneous rock is younger than rocks it has intruded (cut across). • INCLUDED FRAGMENTS: pieces of rock found IN another rock must be OLDER (formed first).

  7. Geologic Time • Using our best data, the Earth is about 4.6 billion years old • That’s 4,600,000,000 years!

  8. How do we know the Earth’s age, and which rocks are older? • Many experiments using radiation found in rocks tell us. • The “Law of Superposition” can also help tell which rocks are older than other rocks.

  9. DIVIDING UP THE EARTH’S AGE • ESRT page 8-9 • Just as we have hours and minutes, Earth’s time has also been broken up into units called ERAS. • The ERAS do not have a set amount of time like the hour. Some ERAS are longer than others. • ERAS are broken down farther into PERIODS.

  10. THE CENOZOIC ERA • The Age of the Mammal • We are currently living in the Cenozoic Era. • The Cenozoic Era has lasted for about 63 million years. • There are only two periods in the Cenozoic Era: • The Tertiary Period • The Quaternary Period - the current period

  11. THE MESOZOIC ERA • Known as the “Age of the Dinosaur” or “Age of the Reptile” • Started about 265 million years ago. • Ended with a mass extinction due to climate change 65.5 million years ago • Contained three periods: • The Triassic • The Jurassic • The Cretaceous

  12. THE PALEOZOIC ERA • Known as the “Age of Fish” • Started about 570 million years ago. • Lasted about 340 million years • Toward the end of this era coal began to form.

  13. The PRECAMBRIAN • Known as “Age of Bacteria” • During much of this time there was no life on earth. • The earth was still hot • The atmosphere was not like it is now- needed bacteria and photosynthetic life to change theCO2 atmosphere into “free oxygen” • The Precambrian Era lasted for the first 4 billion years of Earth’s history.

  14. EARTH’S GEOLOGIC ERAS • PRECAMBRIAN -rocks form, atmosphere • PALEOZOIC -fish, amphibian,coal forms, Appalachian Mt. peak • MESOZOIC -dinosaur, birds, flowers • CENOZOIC -horses, humans, last ice age

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