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| division of earth's history into time units based largely on the TYPES OF LIFE-FORMS that lived during certain periods |
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| LONGEST subdivision in the geologic time scale- based on the abundance of certain TYPES of FOSSILS and is divided into eras, periods and epochs |
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| SECOND longest division of geologic time; is subdivided into periods and is based on major worldwide CHANGES in types of fossils |
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| THIRD longest division of geologic time; is subdivided into epochs and is characterized by the TYPES of LIFE that existed worldwide |
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| next-smaller division of geologic time AFTER THE PERIOD; characterized by DIFFERENCES in LIFE-FORMS that may vary regionally |
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| CHANGE of organisms OVER geologic TIME |
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| GROUP of ORGANISMS that reproduces only with other members of their OWN group |
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| process by which organisms that are suited to a particular environment are BETTER ABLE TO SURVIVE AND REPRODUCE than those thta are not |
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| organism wtih a THREE-lobed exoskeleton that was abundant in Paleozoic oceans and is considered to be an INDEX fossil |
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| large ancient LAND MASS that was composed of all the continents joined together |
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| LONGEST part of Earth's history lasting from 4 billion to 544 million years ago |
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| CHLOROPHYLL-CONTAINING photosynthetic BACTERIA thought to be one of Earth's EARLIEST life-forms |
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| era of ancient life, becag 544 million years ago, when organisms developed HARD PARTS and ended with MASS EXTINCTIONS about 245 million years ago |
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| MIDDLE of Earth's history, during which PANGAEA BROKE APART, dinosaurs appeared and reptiles and gymnosperms (plants that produce seeds but not flowers) were the dominant life-forms |
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| RECENT life that began about 66 million years ago and continues today; includes first apearance of HOMO SAPIENS about 400,000 years ago |
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