Geologists have divided earth's history into time units, which are largely based on?

Which revelation resulted from the observation of the spectrum of different galaxies? a. there were more galaxies whose spectrum was blueshifted b. there were no galaxies whose spectrum was redshifted c. there were more galaxies whose spectrum was redshifted d. there were no galaxies whose spectrum was blueshifted

Largest layer of atmosphere international space station orbits ultraviolet radiation causes ionization the phrases describe what layer of earth's atmosphere?

Acanyon on the ocean floor at which the crust bends downward is called a(n)