NSES Content Standard C  Life Science: Diversity and adaptations of organisms Grades 5-8, page 158 Extinction of a species occurs when the environment changes and the adaptive characteristics of a species are insufficient to allow survival. Fossils indicate that many organisms that lived long ago are extinct. Extinction of species is common; most of the species that have lived on the earth no longer exist.

 
Benchmark 5F The Living Environment: Evolution of Life
Grades K-2, page 123
Some kinds of organisms that once lived on earth have completely disappeared, although they were something like others that are alive today.

Benchmark 5F The Living Environment: Evolution of Life
Grades 3-5, page 123
Fossils can be compared to one another and to living organisms according to their similarities and differences. Some organisms that lived long ago are similar to existing organisms, but some are quite different.

Benchmark 5F The Living Environment: Evolution of Life
Grades 6-8, page 124
Individual organisms with certain traits are more likely than others to survive and have offspring. Changes in environmental conditions can affect the survival of individual organisms and entire species.

Benchmark 5F The Living Environment: Evolution of Life
Grades 6-8, page 124
Many thousands of layers of sedimentary rock provide evidence for the long history of the earth and for the long history of changing life forms whose remains are found in the rocks. More recently deposited rock layers are more likely to contain fossils resembling existing species.