Before the advent of absolute dating methods in the twentieth century, nearly all dating was relative.The main relative dating method is stratigraphy (pronounced stra-TI-gra-fee), which is the study of layers of rocks or the objects embedded within those layers.
Eventually, the entire ecosystem (community of plants and animals) of the planet, including humans, is filled with a concentration of carbon-14.As long as an organism is alive, the supply of carbon-14 is replenished.Dating techniques are procedures used by scientists to determine the age of an object or a series of events.The two main types of dating methods are relative and absolute.The age of the remains of plants, animals, and other organic material can be determined by measuring the amount of carbon-14 contained in that material.
Carbon-14, a radioactive form of the element carbon, is created in the atmosphere by cosmic rays (invisible, high-energy particles that constantly bombard Earth from all directions in space).
By measuring the amount of carbon-14 remaining, scientists can pinpoint the exact date of the organism's death.
The range of conventional radiocarbon dating is 30,000 to 40,000 years.
These include the uranium-thorium method, the potassium-argon method, and the rubidium-strontium method. Thermoluminescence (pronounced ther-moeloo-mi-NES-ence) dating is very useful for determining the age of pottery.
When a piece of pottery is heated in a laboratory at temperatures more than 930°F (500°C), electrons from quartz and other minerals in the pottery clay emit light.
This method is based on the assumption (which nearly always holds true) that deeper layers of rock were deposited earlier in Earth's history, and thus are older than more shallow layers.