Eon: The largest division of geologic time. Examples: Archean Eon, Proterozoic Eon
Era: The largest division of an eon. Examples: Paleozoic Era, Mesozoic Era
Period: The largest division of an era. Examples: Cambrian Period, Jurassic Period
Epoch or Stage: The largest division of a period. Examples: Paleocene Epoch, Pleistocene Epoch
Substage: A division of a epoch or stage.
Boundary: The end of one time division and the beginning of the next. Example: The Permo-Triassic Boundary is the end of the Permian Period and the beginning of the Triassic Period.
Extinction Event: When a large percentage of species die off forever. Example: The extinction event at the end of the Cretaceous Period wiped out all the dinosaurs (except for birds).
Diversity: A measurement of the variety of living things. High diversity means there are a lot of different types of organisms. Low diversity means there are very few different types of organisms.
Radiation: Usually you think of radioactivity on this one, but for evolution we are thinking about a few types of organisms evolving into a great deal of diverse organisms. Example: In the Cambrian Radiation lots of new life forms evolved and diversity of life dramatically increased.
Evolution: The process of a population accumulating inherited changes over time.
Adaptation: a characteristic that helps an organism survive and reproduce in its environment. Adaptations can include structures and behaviors for finding food, for protection, and for moving from place to place. (From Changes Over Time)
Species: a group of organisms that can mate with one another to produce fertile offspring. For example, all red-eyed tree frogs are members of the same species and can mate with one another to produce more red-eyed tree frogs. (From Changes Over Time)
(Note: This definition is a FAIL when it comes to bacteria and archaea for reasons we will discuss later, but it works pretty well for almost all other life.)