HOW DO GEOLOGISTS KNOW HOW OLD A ROCK IS? (PART 1) #Geologist | Geology of the world and the Environment

HOW DO GEOLOGISTS KNOW HOW OLD A ROCK IS? (PART 1)

#Geologists generally know the #age of a rock by #determining the age of the group of #rocks, or formation, that it is found in. The age of formations is marked on a geologic calendar known as the geologic time scale. Development of the geologic time scale and #dating of formations and rocks relies upon two fundamentally different ways of telling time: relative and absolute.

Relative dating places events or rocks in their #chronologic sequence or order of occurrence. Absolute dating places events or rocks at a specific time. If a geologist claims to be younger than his or her co-worker, that is a relative age. If a geologist claims to be 45 years old, that is an absolute age.
Relative Dating

#Superposition: The most basic concept used in relative dating is the law of superposition. Simply stated, each bed in a #sequence of #sedimentary rocks (or #layered #volcanic rocks) is younger than the bed below it and older than the bed above it. This law follows two basic assumptions: (1) the beds were originally deposited near horizontal, and (2) the beds were not overturned after their deposition.
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