In older stars that have burned most of their hydrogen, leftover helium accumulates.
Each helium nucleus has two protons and two neutrons.
While scientists sometimes conceptualize electrons spinning around an atom's nucleus in a defined shell, they actually fly around the nucleus at various distances; this view of the carbon atom can be seen here in two electron cloud figures (bottom), showing the electrons in a single blob (the so-called s-orbital) and in a two-lobed blob or cloud (the p-orbital). It can link to itself, forming long, resilient chains called polymers.
Since atmospheric carbon 14 arises at about the same rate that the atom decays, the Earth's levels of carbon 14 have remained constant.So by measuring carbon 14 levels in an organism that died long ago, researchers can figure out when it died.The procedure of radiocarbon dating can be used for remains that are up to 50,000 years old.The skull was unlike anything seen before, having a flattened cranium with a heavy brow ridge above large eye sockets.Nearby, workers also uncovered an assortment of thick and heavily fossilized bones.