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Earth History

Earth History. Geologic Time Scale. Geologic Time Scale. The geologic Time Scale is a record of Earth’s history The Earth is 4.6 Billion Years Old The names of the divisions do not change however the years designating the beginning and end of these divisions are often reconsidered. Eons.

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Earth History

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  1. Earth History

  2. Geologic Time Scale

  3. Geologic Time Scale • The geologic Time Scale is a record of Earth’s history • The Earth is 4.6 Billion Years Old • The names of the divisions do not change however the years designating the beginning and end of these divisions are often reconsidered

  4. Eons • The time scale is divided into eons • An Eon is the longest time unit and is measured in billions of years

  5. Eons • The history of the Earth is divided into 4 eons: • Hadeon(4.6 Bya-3.8 Bya) • Archaen(3.8 Bya-2.5 Bya) • Proterozoic(2.5 Bya-542 mya) • Phanerozoic(542 mya-Present)

  6. Precambrian • The Precambrian includes the • Hadeon • Archaen • Proterozoic eons. • Includes 90% of Earth’s History • The end of the Proterozoic is defined by the first appearance of organisms with hard parts(shells, skeletons)

  7. Precambrian • Up until the end of the Proterozoic all organisms had soft bodies • Many of these organisms resemble: • Sponges • Snails • Worms

  8. Eras • Eras are the next longest span of time. • Eras are measured in hundreds of millions of years

  9. Eras • The names of the eras of the Phanerozoic are based on their age • “Paleo” means old • “Meso” means middle • “Ceno” means recent • “Zoic” means life

  10. Eras • The Phanerozoic Eon is divided into 3 Eras: • Paleozoic(542 mya-250 mya) • Mesozoic(250 mya-65 mya) • Cenozoic(65 mya-Present)

  11. Paleozoic Era • During the Paleozoic era the oceans had a wide diversity of plants and animals • Trilobites were the dominant organism in the oceans during the early Paleozoic • All trilobites were extinct by the end of the Paleozoic

  12. Paleozoic Era • Land plants and land animals first appeared • At the end of the Paleozoic 90% of marine organisms went extinct • This is considered to be the largest mass extinction event in Earth’s History

  13. Mesozoic Era • The mesozoic era is known for: • The emergence of the dinosaurs • Reef Building corals • Predatory reptiles • Amphibians living on land and in water • Dinosaur population began to decline towards the end and mammals began to evolve

  14. Mesozoic Era • Like the Paleozoic the end of the Mesozoic is marked by a massive extinction event

  15. Cenozoic Era • During the Cenozoic: • Mammals increased in number and diversity • Human ancestors developed • Grasses and flowering plants expanded on land • Ocean life remained relatively unchanged however

  16. Periods • Eras are divided into periods • Periods are usually defined by life forms that appeared or went extinct during that time • Some periods are named for a geographic area in which the first rock of that age was discovered

  17. Periods • The Mississippian period was named for a distinctive limestone that formed along the Mississippi River

  18. Periods • The Jurassic Period is named for the rocks discovered in the Jura Mountains in Europe

  19. Epochs • Periods are divided into Epochs which are measured in millions of years to tens of millions of years • The fossil record the Cenozoic Era is relatively complete • There has been less time for weathering and erosion to destroy the fossil record

  20. Epochs • Certain organisms are used to distinguish the various epochs • Marine Fossils are used to mark the Oligocene • Terrestrial plant fossils are used to mark the Eocene

  21. Relative Dating

  22. Relative Dating Of Rocks • Relative Dating estimates the order of past geologic events by using basic stratigraphic rules • Relative dating does not give us the ages of past events but can tell us the order in which they happened

  23. Relative Dating • Uniformitarianism states that “The Present is the Key to the past”. • In other words processes that are occurring today were more than likely occurring throughout Earth’s history

  24. Geologic Principles • Principle of Superposition • Principle of Original Horizontality • Principle of Cross Cutting Relationships

  25. Principle of Superposition • The principle of superposition states that in an undisturbed rock sequence the oldest rocks are on the bottom and going up they progressively get younger

  26. faculty.icc.edu/easc111lab/labs/labf/prelab_f.htm • Remove frame

  27. Principle Of Original Horizontality • The Principle of Original Horizontality states that sedimentary rocks are deposited in horizontal or nearly horizontal layers

  28. Principle Of Original Horizontality • If the layers are not horizontal then there was an event that caused the layers to fold or tilt

  29. Principle Of Cross Cutting Relationships • The Principle of Cross Cutting Relationships states that a rock that intrudes into another rock is going to be younger than the rock that it is cutting into

  30. The Principle of Cross Cutting Relationships allows us to say that the fault formed after the rock layers formed A fault is always going to be younger than the feature that it cuts through because of the Principle of Cross Cutting Relationships Principle Of Cross Cutting Relationships

  31. Inclusions • Inclusions are pieces of one rock that are contained within another • If a rock layer contains particles of another rock material from the layer beneath it then the layer beneath it is older

  32. Inclusions • The bottom layer became eroded and the loose material became incorporated in the new top layer • A newly formed rock that is Jurassic in age may contain particles that are Ordovician in age

  33. Unconformities • Erosion and flooding can often destroy evidence of past geologic events • Erosional surfaces may be later buried by a younger rock • When a buried erosional surface results in a gap in the rock record it is called an unconformity

  34. Unconformities • There are 3 types of unconformities: • Disconformity • Nonconformity • Angular Unconformity

  35. Disconformities • A disconformity is an unconformity between parallel layers of sedimentary rock which represent a period of erosion or non-deposition

  36. Nonconformities • A nonconformity is a break that separates older metamorphic or intrusive igneous rocks from younger sedimentary rocks

  37. Angular Unconformity • An angular unconformity consists of a tilted sedimentary rock that is overlain by a younger more flat lying strata

  38. Correlation • Correlation is the matching of outcrops of one geographic region to another

  39. Absolute Dating

  40. Absolute Dating Techniques • Absolute dating allows scientists to determine the actual age of a rock, fossil or other object • Scientists use radioactive decay to determine the ages of rocks

  41. Radioactive Decay • Radioactive substances emit particles at a set rate • As they emit particles the number of protons and neutrons change and the element is converted into a different element • Radioactive dating is the emission of radioactive particles and the resulting change into other elements

  42. Radiometric Dating • Radiometric dating is the process in which scientists determine the ratio of parent nuclei to daughter nuclei • After they determine the ratio of parent to daughter nuclei they can figure out the actual age of the object

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