Geoscience Reference
In-Depth Information
Ion. A particle bearing a negative or positive charge.
ITCZ (Intertropical Convergence Zone). The contact zone between the Trade Winds
of the Northern and Southern hemispheres. Shifts its position north and south of
the Equator with the seasons and, when overhead, usually brings rain.
Lagomorph. A rabbit, hare, or pika. A member of the Order Lagamorpha.
Laterite. A hardpan that forms in red tropical soils (oxisols) due to the concentration of
iron oxide.
Latitude. The distance of a point north or south of the Equator (0
latitude), measured
in degrees.
Leaching. The process in which dissolved substances are removed from the substrate
by the downward percolation of water.
Legume. Any plant that is a member of the pea and bean family (Leguminoseae) or, in
other taxonomic schemes, Mimosaceae, Caesalpinaceae, or Fabaceae. Many of
these plants have symbiotic relationships with rhizobial bacteria on their roots that
fix atmospheric nitrogen into nitrates, which are important plant nutrients.
Loess. Powder-like material deposited by the wind. The most fertile temperate soils,
the chernozems, are generally developed on this type of substrate.
Marsupial. A nonplacental mammal of the order Marsupalia whose young develop
attached to teats in a pouch. Considered an early or primitive form of mammal,
marsupials dominate the mammalian fauna of Australia and are also diverse in the
Neotropics.
Mediterranean. Refers to regions or climate patterns in which winter is the rainy sea-
son and summers are dry.
Migration. The seasonal movement of a population from one area to another with a
return to the original range when seasons change.
Monsoon. A wind that reverses its direction seasonally. An onshore flow typifies the
warm season and an offshore flow occurs during the cold season. The Asian mon-
soon is most powerful and dominates the climate of the vast Indian Ocean region.
More localized monsoonal
systems occur elsewhere, as in the American
Southwest.
Neotropical. Pertaining to the region from southern Mexico and the Caribbean to
southern South America and to animals and plants restricted or nearly restricted to
this region.
Nitrogen-fixing. The ability to convert elemental or pure nitrogen to nitrates. Only cer-
tain microorganisms can do this and hence they are vital to higher lifeforms that
require nitrogen but cannot utilize it in its pure form. Rhizobial bacteria and cyano-
bacteria in the soil are important nitrogen-fixers in terrestrial ecosystems.
Perennial. A plant that lives two or more years.
Perissodactyl. Any of the odd-toed ungulates. Living forms include zebras, rhinocero-
ses, and tapirs.
Polar Front. In the global atmospheric circulation system, the contact zone between
cold polar air and warmer subtropical airmasses. Associated with uplift at the sub-
polar lows and often stormy, wet weather patterns in the mid-latitudes.
Rainshadow. A dry region that develops on the lee (downwind) side of mountain
ranges. Low amounts of precipitation are the result of the warming of airmasses as
they descend the mountain slopes.
