Convergent Boundary		A major division on the geologc time scale, eras are divided into shorter units called periods
Divergent Boundary		a circulation in which material is heated and rises in one area, then cools and sinks in another area
Pangea		Process by which rocks are placed in their sequence or order
Period		A basic unit of the geologic time scale that is a subdivision of an era, periods may be divided into smaller units called epochs
Eon		The proposed supercontinent that 200 million years ago began to break apart and form the present landmass
Relative Dating		A boundary along which tewo tectonic plated push together
Era		A switch in the direction of Earth's magnetic north pole becomes the magnetic south pole
Subduction		The process by which an oceanic plate sinks under another plate
Epoch		The concept that processes that have shaped Earth in the past that are essentially the same as those operating today
Magnetic Reversal		A law that states that in any undeformed sequence of sedimentary rocks, each bed is older then the layers above and younger than the ones below
Fossil		A boundary along which two tectonic plates pull apart
Index Fossils		A fossil that is associated with a particular span of geologic time
Half-Life		The largest time unit on the geologic time scale, next in order of magnitude above era
Law of Superposition		An area where a column of hot material rises from deep within the planet's mantle
Uniforimitarianisum		The time required for one half of the atoms of a radioactive substance to decay
Hot Spot		A unit of the geologic time scale that is a subdivision of a period
Convection Current		The remains or traces of an organism preserved from the geologic past