Phanerozoic literally "visible animal life", the most recent of the four eons of geologic time. Proterozoic The name means the era of "first (animal) life".This was the third eon in Earth history, during which eukaryote life and an oxygen atmosphere appeared.An atom may share electrons with an adjacent atom or atoms; the result being a molecule.
Cosmic rays Very high energy particles which fly through space.
During this time prokaryote life appeared and flourished, and the Earth was characterised by a reducing (anaerobic) atmosphere. Atom The smallest unit that has the chemical characteristics of a particular chemical element.
It is about ten billionths of an inch in diameter and is made of a dense central nucleus of protons and neutrons, surrounded by a cloud of electrons.
Electron-capture decay The only type of radioactive decay that requires the presence of something — an electron — outside the atom's nucleus.
Electron capture decay of light atoms — those having the fewest electrons — can be very slightly affected by extremely high pressures or certain chemical bonds, so as to change their half-lives by a fraction of a percent.