Uniformitarianism: the theory that changes in the earth's crust during geological history have resulted from the action of continuous and uniform processes.
Trace fossil: a fossil of a footprint, trail, burrow, or other trace of an animal rather than of the animal itself
A. Oxygen. Oxygen has an atomic mass of 16. The atomic mass of an atom is the combined weight o the protons and neutrons. Since Oxygen's atomic mass is 16, it has 8 protons and 8 neutrons.
