Earth's Geologic History
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33 terms
Terms | Definitions |
|---|---|
 fossil | The preserved remains or traces of living things. |
| paleontologist | A scientist who studies fossils to learn about organisms that lived long ago. |
| sedimentary rock | The type of rock that is made of hardened sediment |
| petrified fossil | A fossil in which minerals replace all or part of an organism. |
| mold | A fossil formed when an organism buried in sediment dissolves, leaving a hollow area. |
| cast | A fossil that is a copy of an organism's shape, formed when minerals seep into a mold. |
| carbon film | A type of fossil consisting of an extremely thin coating of carbon on rock. |
| trace fossil | A type of fossil that provides evidence of the activities of ancient organisms |
| scientific theory | A well-tested concept that explains a wide range of observations. |
| evolution | The process by which all the different kinds of living things have changed over time. |
| extinct | Describes a type of organism that no longer exists anywhere on Earth. |
| relative age | The age of a rock compared to the ages of rock layers. |
| absolute age | The age of a rock given as the number of years since the rock formed. |
| law of superposition | The geologic principle that states that in horizontal layers of sedimentary rock, each layer is older than the layer above it and younger than the layer below it. |
| unconformity | A place where an old, eroded rock surface is in contact with a newer rock layer. |
| fault | A break or crack in Earth's lithosphere along which the rocks move. |
| intrusion | An igneous rock layer formed when magma hardens beneath Earth's surface. |
| extrusion | An igneous rock layer formed when lava flows onto Earth's surface and hardens. |
| index fossil | Fossils of widely distributed organisms that lived during only one short period of time. |
| atom | The smallest particle of an element. |
| element | A type of matter in which all the atoms are the same. |
| radioactive decay | The breakdown of a radioactive element, releasing particles and energy. |
| half-life | The time it takes for half of the atoms of a radioactive element to decay. |
| geologic time scale | A record of the geologic events and life forms in Earth's history. |
| era | One of the three long units of geologic time between the Precambrian and the present. |
| invertebrate | An animal without a backbone. |
| period | One of the units of geologic time into which geologists divide eras. |
| epoch | Subdivisions of the periods of the geologic time scale. |
| vertebrate | An animal with a backbone. |
| amphibian | A vertebrate that lives part of its life on land and part of its life in water. |
| reptile | A vertebrate with scaly skin that lays eggs with tough, leathery shells. |
| mass extinction | When many types of living things become extinct at the same time. |
| mammal | A warm-blooded vertebrate that feeds its young milk. |
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