Dating of rocks fossils and geologic events laboratory 8
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).
Since certain species of animals existed on Earth at specific times in history, the fossils or remains of such animals embedded within those successive layers of rock also help scientists determine the age of the layers.
Similarly, pollen grains released by seed-bearing plants became fossilized in rock layers.
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.
The successive layers of rock represent successive intervals of time.
Radioactive decay: The predictable manner in which a population of atoms of a radioactive element spontaneously disintegrate over time.
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.Narrow rings grow in cold or dry years, and wide rings grow in warm or wet years.The rings form a distinctive pattern, which is the same for all members in a given species and geographical area.Absolute dates must agree with dates from other relative methods in order to be valid.The most widely used and accepted form of absolute dating is radioactive decay dating. Radioactive decay refers to the process in which a radioactive form of an element is converted into a nonradioactive product at a regular rate.