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A sudden release of energy in the Earth’s crust that creates seismic waves. Earthquakes are common at active plate boundaries.


A member of the Phylum Echinodermata, which includes starfish, sea urchins, and crinoids. Echinoderms have radial symmetry (which is usually five-fold), and a remarkable ability to regenerate lost body parts.


A member of a group of primitive sharks from the Carboniferous period known for their “tooth-whorls,” unusual serrated teeth that grew in curved brackets and were used like the teeth in pinking shears.


An extinct class of echinoderm that had a simple, cushion-shaped body and five arms.
See also: echinoderm


To foam or fizz while releasing gas. Carbonate minerals will effervesce when exposed to hydrochloric acid.


The use of a relatively small amount of energy for a given task, purpose, or service; achieving a specific output with less energy input.


A bay, such as where the sea overflows a depression of land near the mouth of a river, or where there is a recess in a coastline.


Native to a particular geographic area or range.


The power derived from the use of physical or chemical resources. Everything we do depends upon energy—without it there would be no civilization, no sunlight, no food, and no life. Energy moves people and goods, produces electricity, heats our homes and businesses, and is used in manufacturing and other industrial processes.

energy carrier

A source of energy, such as electricity, that has been subject to human-induced energy transfers or transformations.


An extinct family of omnivorous artiodactyl mammals that look somewhat like pigs but are actually thought to be more closely related to hippos. They roamed the forests and plains of North America, Europe, and Asia during the Eocene and Miocene. Entelodonts had bulky bodies and powerful teeth, and some grew up to 2 meters (7 feet) tall at the shoulder.


A soil order ; these are soils of relatively recent origin with little or no horizon development. They are commonly found in areas where erosion or deposition rates outstrip rates of soil development, such as floodplains, mountains, and badland areas.


A geologic time period extending from 56 to 33 million years ago. The Eocene is an epoch of the Paleogene period.


The transport of weathered materials. Rocks are worn down and broken apart into finer grains by wind, rivers, wave action, freezing and thawing, and chemical breakdown.
Over millions of years, weathering and erosion can reduce a mighty mountain range to low rolling hills. Some rocks wear down relatively quickly, while others can withstand the power of erosion for much longer. Softer, weaker rocks, such as shale and poorly cemented sandstone and limestone, are much more easily worn than hard, crystalline igneous and metamorphic rocks, or well-cemented sandstone and limestone. Harder rocks are often left standing as ridges because the surrounding softer, less resistant rocks were more quickly worn away.

erratic, glacial erratic

A piece of rock that differs from the type of rock native to the area in which it rests, carried there by glaciers often over long distances.
Erratics are often distinctive because they are a different type of rock than the bedrock in the area to which they have been transported. For example, boulders and pebbles of igneous and metamorphic rocks are often found in areas where the bedrock is sedimentary; it is sometimes possible to locate the origin of an erratic if its composition and textures are highly distinctive.


A sinuous, elongated ridge of sand and gravel. Most eskers formed within ice-walled tunnels carved by streams flowing beneath a glacier. After the ice melted away, the stream deposits remained as long winding ridges.
Eskers are sometimes mined for their well-sorted sand and gravel.


A place where freshwater and saltwater mix, created when sea level rises to flood a river valley.


Organisms with complex cells containing a nucleus and organelles. Protists and all multicellular organisms are eukaryotes.


A marine invertebrate animal belonging to the extinct Order Eurypterida of the Subphylum Chelicerata in the Phylum Arthropoda, and characterized by a large flat carapace, a segmented tail, walking legs, and swimming paddles. Paleontologists believe that eurypterids lived in nearshore environments, including salty, shallow, environments like the Silurian inland ocean. Although known as “sea scorpions,” they are not related to today’s scorpions. Their closest living relatives are horseshoe crabs. Eurypterids were apparently one of the great predators of their time, reaching as much as 9 feet (3 meters) in length. The largest complete eurypterid in the world, approximately 4.3 feet (1.3 meters) long, was found in New York State and is on display at the Museum of the Earth in Ithaca, New York.


A sedimentary rock created by the precipitation of minerals directly from seawater, including gypsum, calcite, dolomite, and halite.


A type of physical weathering. When overlying layers are weathered away, the reduction of downward pressure allows the underlying rock to expand toward the surface. This expansion causes joints, or cracks, to form parallel to the surface, producing slabs that resemble the curved layers of an onion.


The erosional uncovering or exposing of a geological feature that had been previously covered by deposited sediments.


To come out of solution and, in the case of a gas, form bubbles.


The end of species or other taxonomic groups, marked by death of the last living individual. Paleontologists estimate that over 99% of all species that have ever existed are now extinct. The species of modern animals that we study in biology today represent less than 1% of what has lived throughout geologic time.

extrusion, extrusive rock

An igneous rock formed by the cooling of lava after magma escapes onto the surface of the Earth through volcanic craters and cracks in the Earth’s crust.