When was the last epoch in which organisms could start walking across the bering strait and panama canal? pliocene pleistocene holocene eocene

The answer is; Holocene.

The Bering Strait is located in the Arctic circle and is a small continental gap between Russia and Alaska. About 11, 000 years ago, the ice age locked up most of the water the polar circles hence the ocean levels were lo exposing the Bering Strait crossing. This allowed organisms to cross between the two continents.

the relative atomic mass of an element is the mass of one atom of that element, relative to 1/12th of the mass of a  1212c atom. to convert to an absolute mass in kg, it is necessary to multiply by  1.661×10−271.661×10−27.

the relative atomic mass is roughly equal to the number of neutrons, plus the number of protons, in the nucleus of the atom.

for elements with more than one stable isotope (different types of nucleus with different numbers of neutrons but the same number of protons), the quoted mass is usually the average mass, weighted by the relative abundance of the different isotopes.

not sure if this is what you'r looking for nnew= nold