MID-Terms and Definitions
Minerals: The basic pieces of solid rock; a particular mineral is distinguished from the other
minerals by its chemical composition or crystal structure (or both)
Rocks: Intact solids that may contain a variety of minerals. We classify rocks into three basic
types by their formation process: Igneous rock is of volcanic origin, made when molten rock
cools and solidifies. Sedimentary Rock is made by gradual compression of sediments, which may
contain bits of other rocks as well as fossils. Metamorphic Rock was once either igneous or
sedimentary but has since been transformed (but not melted) by high heat or pressure. Rocks of
any of the three types may be sub classified by the minerals they contain.
Fossil: Any relic left behind by living organisms that died long ago.
TERMS RELATED TO GEOLOOGICAL TIME:
Geological Record: the information about Earths past that is recorded in rocks and fossils; the
latter record is sometimes called fossil record.
Geological time scale: The time scale used to measure the history of Earth.
Radiometric Dating: The method of determining the age of a rock or fossil from the study of
radioactive isotopes contained within it.
Half-life: The time it takes for half of the atoms to decay in a sample of radioactive substance.
TERMS RELATED TO EARTHS GEOLOGICAL HISTORY:
Differentiation: A process in which materials separate by density. In Earth, differentiation led to
a dense core made mostly of iron and nickel, a rocky mantle made mostly of silicates (minerals
rich in silicon and oxygen), and a crust made of lower-density rocks.
Heavy Bombardment: The period of time during which the planets were heavily bombarded by
leftover planetesmals, starting from the time the planets first formed and ending some 3.8-4.0
billion years ago.
Late Heavy Bombardment: An apparent increase in the impacts rate near the end of the heavy
bombardment, between about 4.1 and 3.8 billion years ago.
Outgassing: The process of releasing gases trapped in a planetary interior into the atmosphere.
Lithosphere: The layer of cooler more ridged rock that sits above the warmer, softer mantle rock
below. It encompasses both the crust and the uppermost portion of the mantle, extending to a
depth of about 100 kilometres. On Earth, the Lithosphere is broken into a set of large plates.
Seafloor Crust: The relatively dense, thin, young crust found on Earths seafloors, composed
largely of the igneous rock called basalt.
Continental Crust: The thicker, lower-density crust that makes up Earths continents. It is made
when remelting of seafloor crust allows lower-density rock to separate, and typically consists of
granite. Continental crust ranges in age from very young to as old as 4.0 billion years ago.
Plate Tectonics: The geological process in which lithospheric plates move around the surface of
Earth. It acts like a conveyor belt, with new seafloor crust erupting and spreading outward from
mid-ocean ridges and then being recycled back into the mantle by subduction at ocean trenches. It also explains Continental drift, because plates carry the continents with them as
TERMS RELATED TO CLIMATE AND CLIMATE REGULATION
Greenhouse Effect: The effect that makes a planet’s surface warmer than it would be in the
absence of an atmosphere. It is caused by the presence of Greenhouse gases—such as
carbon dioxide (CO 2), water vapour (H20), and methane (CH 4)—that can absorbed infrared
light emitted by the planetary surface (after the surface is heated by sunlight)
Carbon Dioxide Cycle (CO 2cycle): The cycle that keeps the amount of carbon dioxide in the
Earth’s atmosphere small and nearly steady and hence keep the Earth habitable. Over time,
this cycle has locked up most of Earth’s carbon dioxide in carbonate rocks (rocks rich in
carbon and oxygen) such as limestone.
Ice Ages: Periods of time in which Earth becomes unusually cold, so water from the oceans
freezes out as ice and covers a substantial portion of the continents.
Snowball Earth: Refers to periods of extreme ice ages that may have occurred several times
before about 580 million years ago.
Global Warming: Usually refers to the current warming of Earth caused by human input of
greenhouse gases into the atmosphere.
Chapter 5 Terms and Definitions
TERMS RELATED TO EVOLUTION
Evolution (biological): the gradual change in populations of living organisms that has
transformed life of Earth from its primitive origins to the great diversity of life today.
Evolutionary Adaption: An inherited trait that enhances an organism’s ability to survive and
reproduce in a particular environment.
Theory of Evolution: The Theory, first advanced by Charles Darwin that explains how and