UCMP Glossary: I

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Iapetus Ocean -- n. A relatively small ocean that existed between the continents of Laurentia, Baltica, and Avalonia from the Late Precambrian to the Devonian.

Ichnology -- The study of trace fossils.

igneous rock -- Any rock solidified from molten or partly molten material.

impressions -- Prints or marks made when an organismís body has been compressed (flattened). Impressions are different from compressions because no thin organic material is left behind.

incubation -- n. In birds and reptiles, the maintaining of a constant temperature during the development of the embryo. Birds incubate their eggs by sitting on them (also called brooding),while other animals, like crocodiles, bury their eggs in organic matter. If eggs are not incubated, the embryos within those eggs generally die. Some dinosaurs may have incubated their eggs by burial in sediment, in organic matter, or by brooding like birds.

inflorescence -- A cluster of flowers.

ingestion -- The intake of water or food particles by "swallowing" them, taking them into the body cavity or into a vacuole. Contrast with absorption.

ingroup -- In a cladistic analysis, the set of taxa which are hypothesized to be more closely related to each other than any are to the outgroup.

inorganic -- adj. Not containing carbon. Not from living things, e.g., minerals, water, oxygen, etc.

integrin -- adhesive protein of the extracellular matrix in animals.

interbedded -- adj. Describes beds (layers) of rock lying between or alternating with beds of a different kind of rock.

internode -- The region of a stem between two nodes, when there is no branching of the vascular tissue.

intertidal -- The coastal zone measuring from the lowest to the highest tide mark. The intertidal zone is subject to alternating periods of flooding and drying.

intestine -- The portion of the digestive tract between the stomach and anus; it is the region where most of the nutrients and absorbed.

intrusion -- n. Magma (and the rock it forms) that has pushed into pre-existing rock; intrusive- adj.; plutonic- syn. extrusive- ant.

ion -- an atom or small molecule which carries a positive or negative charge.

island arc -- n. A curved chain of islands that rise from the sea floor, usually near a continent. The convex side usually faces the open ocean, while the concave side usually faces the continent, e.g., the Aleutian Islands in Alaska; volcanic arc- syn.

isotope -- One of two or more variations of the same chemical element, differing in the number of neutrons not the number of protons.

isotopic analysis -- n. The study of the geochemistry of stable isotopes in naturally occurring sediments and biological structures. Stable isotopes are atomic variations of elements that are stable over long periods of time, meaning they do not radioactively decay. Several elements, like oxygen and carbon, have several stable forms. Oxygen, for example, occurs in nature as 16O and 18O ó these two forms are isotopes. They have different numbers of neutrons (16O has two more neutrons than 18O), and and is therefore heavier. Because the two isotopes have different masses, chemical and physical reactions like bonding, evaporation, and precipitation occur at different frequencies. The ratio of stable isotopes is preserved in chemical compounds like water, ice, and calcium carbonate and provides information on the environmental conditions at the time the compound formed. For example, the ratio of 18O/16O in an ice sample is linked to the water temperature of ancient oceans, which in turn reflects ancient climates.

Last updated:2009-11-12