Select the correct answer. How is relative-age dating used to determine the ages of fossils?
A.
by observing the formation of sedimentary rocks
B.
by using radioactive isotopes
C.
by estimating the number of fossils in a particular region
D.
by the formation of igneous rocks
E.
by identifying the way the fossils were formed

Which of the following best explains the changes in biodiversity shown in the graph?

Arrange these steps in the correct order to explain how a muscle fiber contracts

Which of the following is true? species on earth today are but a fraction of all species that ever lived. the number of species existing at one time has decreased throughout history. extinctions of past species has happened gradually and on a small scale. most organisms present early in earth's prehistory were more complex than modern organisms. "bacteria represent a newer form of life, not present during the early prehistory of earth."