Ages of the Earth- Ch. 9
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27 terms
Terms | Definitions |
|---|---|
 Petrified Remains | "Turned to stone" minerals replace all or part of the organism |
| mold | hollow area in sediment in the shape of an organism |
| cast | a copy of the shape of an organism |
| carbon film | extremely thin coating of carbon on rock, gases from decaying organisms escape into the sediment leaving behind a thin layer of carbon |
| Trace fossils | evidence of activities of past organisms, footprints, burrows |
| Preserved remains | tar, amber (petrified tree sap), frozen remains (like the woolly mammoth |
| Evolution | the gradual change of living things over time |
| Scientific Theory | a well tested concept that explains a wide range of observations |
| Extinct | an organism that no longer exists, and will never again live on Earth |
| Five types of fossils that can be found in rock | carbon film, mold and cast, petrified, preserved remains, trace |
| Relative age | for a rock, is the age compared to the age of other rocks |
| Absolute age | for a rock, the exact (as possible) number of years since the rock formed |
| First Clues to relative age | The Law of Superposition- in horizontal layers of sedimentary rock the oldest layers are at the bottom. Each higher layer is younger than the layer below |
| Second Clues to relative age | Igneous rock Extrusion 1. layer once on the surface 2. layers below are always older |
| Clues to relative age | Igneous rock Intrusion 1. welling uplift of magma that went through layers 2. intrusion is always younger than the layers around the intrusion and layers below an intrustion |
| fault | break in the Earth's crust- The fault is always younger, than the layers of rock the fault cuts through. |
| Unconformity | A gap in the geologic record. Some layers have been lost due to erosion. New rock layers are on top of very much older layers. |
| Index fossils | Used to date the relative ages of the rock layers they are found in. |
| Requirements to be an index fossil | 1. Organism must be widely distributed (was found nearly everywhere on Earth) 2. Organism that existed only briefly, then died out. |
| Stromatolites | fossilized bacteria grew like stacks of pancakes, estimated at 3 billion years old, one of the oldest living things found on Earth. |
| Radioactive decay | Atoms of one element breakdown to form more stable atoms of another element. The rate of decay of each different radioactive element is constant- it never changes. |
| Half-life | The time it takes for half of the radioactive element to decay. |
| Why do scientists use radioactive dating | To determine the absolute ages of rock |
| Potassium- Argon | Dating is useful for dating ancient rock half-life of 1.3 billion years |
| Carbon-14 | Dating is useful up to 50,000 years because of its short half-life of 5,730 years |
| How old is Earth? | A little older than 4.6 billion years is currently accepted |
| Fossil record | Provides evidence of the history of life on Earth. Shows that different groups of organisms have changed over time. |
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