Absolute and relative fossil dating
A further issue is known as the "old wood" problem.It is possible, particularly in dry, desert climates, for organic materials such as from dead trees to remain in their natural state for hundreds of years before people use them as firewood or building materials, after which they become part of the archaeological record.The half-life of potassium-40 is 1.3 billion years, far longer than that of carbon-14.With this method, the older the specimen, the more reliable the dating.Absolute dating is the process of determining a specific date for an archaeological or palaeontological site or artifact.
Other radiometric dating techniques are available for earlier periods.
Furthermore, whereas carbon-14 dating can be done only on organic remains, K-Ar dating can be used only for inorganic substances: rocks and minerals.
As potassium-40 in rocks gradually breaks down into argon-40, the gas is trapped in the rock until the rock is heated intensely (as with volcanic activity), at which point it may escape. Dating is done by reheating the rock and measuring the escaping gas.
©1 Return to: Human evolution index page (see books) About six or seven million years ago there were no bipedal creatures resembling humanity.
The earth was rich with diverse life forms, all subject to and shaped by natural forces and not the slightest signs of the intelligence and creativity that typifies humanity.