Common isotopes for radiometric dating
The atom's atomic mass number stays the same because the total number of protons and neutrons remain the same. Biostratigraphic zone unit of geologic time defined by the presence of one or more fossil species.
Interval zones use the range of single species, assemblage zones use the ranges of a group of species, while abundance zones use maximum or minimum abundances instead of just presence and absence data. The third and current (most recent) geologic era of the Phanerozoic Eon, which began 65.5 million years ago; colloquially referred to the "Age of Mammals".
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.
In reality there is always some exchange or influence, but if this amount is completely insignificant for the process under consideration (e.g., for dating, if the loss or gain of atoms is insignificant) for practical purposes the system can be considered closed.
Cosmic rays Very high energy particles which fly through space.
Plants include Pteridophytes, later supplemented by early gymnosperms. Usually contrasted with the Precambrian, in which life is little known and generally microscopic.
But no change in the half-lives of elements used for radiometric dating has ever been verified.
Element A substance, made up of atoms, that cannot be further subdivided by chemical means.
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.