Sandstone, shown below, is one kind of rock that forms in horizontal layers layers are toward the bottom and If a stack of rock layers has not been disturbed since it formed, the the layers are toward the top. ​

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.

sound moves fastest in solids because the molecules are tightly packed and it allows sound to vibrate