Geologic Time. What is Age? Absolute Age The number of years since the rock formed. (150 million years old, 10 thousand years old.

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1 Geologic Time There are 2 kinds: What is Age? Absolute Age The number of years since the rock formed. (150 million years old, 10 thousand years old.) Relative Age The age compared to the ages of other rocks. (older than this rock, younger than that rock.) 1

2 Law of superposition Which layer is oldest?» Diagram this! 2

3 Law of cross-cutting Which layer is older 4 or 3?» Diagram this! 3

4 Law of Horizontality Draw this! A BREAK in the Earth s crust. A fault is always YOUNGER than the rock it cuts through. 4

5 What is an Unconformity? The surface where new rock layers meet a much older rock surface beneath them. An unconformity shows where some rock layers have been lost because of erosion. Unconformity 5

6 Put in order! Geologic time Gigaannus: Ga= Billion years Billion years ago: BYA 6

7 Major divisions of geologic time Precambrian Paleozoic Cenozoic Mesozoic Early Earth History Precambrian Longest time unit Biological events Primordial puddle Amino acids formed Invertebrates developed 7

8 Geologic events Precambrian, contd Very volcanic, many igneous rocks formed Little is known about this era, because rocks were eroded, heated and pressurized, invertebrates are soft. Paleozoic Era MYA Biological events Mostly marine life forms: Trilobites Brachiopods and Crinoids still exist today Fish 8

9 Clicker Divisions between ERAS in geologic time is based on? a)mass extinctions b)ice ages c)exfoliation d)volcanic eruptions Timer Times up! SMART Response Q To set the properties right click and select SMART Response Question Object->Properties Paleozoic, cont Appalachian Mountains started forming First vertebrates Plant life moved from ocean to land Then animals moved to land. Pangaea came together and major glaciers formed, caused mass extinctions of animals. 9

10 Mesozoic Era MYA Divided into three periods: Triassic Jurassic Cretaceous Mesozoic, contd Triassic period Pangaea separated Climate dried out Small dinosaurs appeared First mammals 10

11 Mesozoic, contd Jurassic Reptiles dominated Big dinosaurs! Birds appeared Mesozoic, cont d Pangaea breaks up (completely) Volcanic activity Dinosaurs become extinct 11

12 Cenozoic, 66.4 MYA to present Ice ages occurred Himalayan mountains formed Further evolution of plants and animals. Insects, small animals, Modern Humans appeared 200,000 years ago Fossil Evidence such as the remains, imprints or traces of once living organisms preserved in rocks. 12

13 Fossil types Replacement fossil- form when bones, teeth or shells are replaced by minerals dissolved in water. Carbonization fossil- forms when an animal is compressed, leaving behind a carbon film on the surrounding rock. Fossil types Cast/Mold Cast- the part that is the shape of the original object. Mold- the cavity in the rock. 13

14 Fossil types Original remains- insects can be completely preserved in crystallized tree sap (amber). Trace fossils- fossilized tracks and other evidence of animal activity. o Footprints o Burrow holes o Coprolites 14

15 Michigan s Geologic History Precambrian o Metamorphic rock o MI was tectonically active o Copper and Iron o Fossilized algae (stromatolites) Paleozoic o MI was tropical Ocean (salt water) Coral => Petoskey stones MI basin bowl shaped o Youngest rocks in the center older as you move away Michigan s Geologic History Mesozoic o Jurassic rock the youngest what happened to the rest? Stolen! Unconformity What fossils would you not expect to find? o Sorry no dinosaurs in your backyard Cenozoic o Glaciers 15

16 ABSOLUTE DATING Absolute dating- Any method used to determine the age, in years, of a rock or other object. Radiometric Dating Carbon dating Uranium dating Other methods dendrochronology RADIOMETRIC DATING Some isotopes of some elements break down (decay) into other elements over time. These are called radioactive isotopes. 16

17 EXAMPLES OF RADIOACTIVE ISOTOPES 238 Uranium decays to 206 Lead 14 Carbon decays to 16 Nitrogen Parent product (Unstable) daughter product (stable) RADIOMETRIC DATING We know how long it takes uranium to decay to lead. This rate of decay is known as its half-life. This rate is quantifiable. 17

18 HALF-LIFE The half-life is the time it takes for half of the atoms of the parent product to decay to the daughter product. 14 C = 5,730 years 238 U = 4.5 billion years 40 K = billion years C-14 C-14 N-16 1 half life It would take 5,730 years for half of the 14 C atoms in an object to decay to 16 Nitrogen 18