3.2a In all environments, organisms with similar needs may compete with one another
3.2b Extinction of a species occurs when the environment changes and the adaptive
characteristics of a species are insufficient to permit its survival. Extinction of species is
common. Fossils are evidence that a great variety of species existed in the past.
3.2c Many thousands of layers of sedimentary rock provide evidence for the long his-
tory of Earth and for the long history of changing lifeforms whose remains are found in
the rocks. Recently deposited rock layers are more likely to contain fossils resembling
3.2d Although the time needed for change in a species is usually great, some species of
insects and bacteria have undergone significant change in just a few years.