Ch. 17 Geologic Time Vocabulary Review

Term Definition
eon The longest unit of geologic time.
era A large division of geologic time that is smaller than an eon.
period A unit of geologic time smaller than an era.
epoch A division of geologic time smaller than a period.
mass extinction The extinction of many species on Earth within a short period of time.
landbridge A landform that connects two continents that were previously separated.
geographic isolation The separation of a population of organisms from the rest of its species due to some physical barrier such as a mountain range or an ocean.
Paleozoic Era The oldest era of the Phanerozoic eon.
Mesozoic Era The middle era of the Phanerozoic eon.
Cenozoic Era The youngest era of the Phanerozoic eon.
inland sea A body of water formed when ocean water floods continents.
coal swamp An oxygen-poor environment where, over a period of time, decaying plant material changes into coal.
supercontinent An ancient landmass which separated into present-day continents.
dinosaur Dominant Mesozoic land vertebrates that walked with their legs positioned directly below their hips.
plesiosaur Mesozoic marine reptile with a small head, long neck, and flippers.
pterosaur Mesozoic flying reptile with large, bat-like wings.
Holocene Epoch The current epoch of geologic time which began 1-,000 years ago.
Pleistocene Epoch The first epoch of the Quaternary period.
ice age A period of time when a large portion of Earth's surface is covered by glaciers.
glacial groove Grooves in solid rock formations made by rocks that are carried by glaciers.
mega-mammal A large mammal of the Cenozoic era.
plate tectonics The theory that Earth's surface is broken into large, rigid pieces that move with respect to each other.
mid-ocean ridge A long, narrow mountain range on the ocean floor; formed by magma at divergent plate boundaries.
seafloor spreading The process by which new oceanic crust forms along a mid-ocean ridge and older oceanic crust moves away from the ridge.

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