Why did seed production help plants move to land?

This increased the chance of growth and development of plants to spread. When pollen grains land on the stigma of the correct species, they germinate. ... The nucleus of the pollen grain (male gamete) then passes along the pollen tube and joins with the nucleus of the ovule (the female gamete)

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.