Geologic Time
About Geologic Dating/Relative Dating
In geologic dating, we look at sediments and multiple layers of the earth in order to determine how old the planet is. The most bottom layer of various formations will be the oldest, and the top layer would be the youngest. This is called The Law of Superposition. When sediments are laid down one above the other in an uninterrupted succession the strata so formed are said to be in a state of conformity. There are 4 types of conformity we look at and can use in geologic dating:
nonconformity: sedimentary rocks overlying crystalline rocks
angular conformity: flat-lying sedimentary rocks overlying tilted sedimentary rocks
disconformity: erosional separation between two sedimentary rocks
para-conformity: no visible gap in time but ages above and below the para-conformity indicate a time gap.
index fossils: unique and have very specific time frame they lived in.
William Smith: created the first detailed, nationwide geological map of any country.
A geologic map shows the distribution of materials at or near the Earth's surface. Smith's map and ideas paved the way for a better understanding of geological time and laid the founding principles for geological surveys worldwide.
Dendrochronology: Dendrochronology is the science or technique of dating events, environmental change, and archaeological artifacts by using the characteristic patterns of annual growth rings in timber and tree trunks. The rings of the tree show how long the tree has been growing and can range from a couple years to over a 100.
Radiometric Dating
Radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed.
The difference between relative and radioactive dating is that relative dating determines the relative age of rock layers according to their relative depth. However, radiometric dating determines the absolute age with the use of decaying products of the natural radioactive isotopes.
Relative dating and radioactive dating are two methods in archaeology to determine the age of fossils and rocks. The study of fossils is important for the determination of the kind of organism it represents, how the organism lived, and how it was preserved on the Earth's surface over the past 4.6 billion years.
International Chronostratigraphic Chart
The international chronostratigraphic