Geological time is divided into supereons, eons, eras, and periods. Stratigraphy is used to study rock layers and establish critical points in time. Dating can be imprecise due to vast time spans. Geological history is used to study climate, evolution, and the Earth’s formation. Disputes can arise due to inaccurate dating or lack of information.
Scientists believe the Earth is nearly five billion years old, meaning the third rock from the Sun has seen a lot of history. Human history has occupied only a small fraction of Earth’s total existence, so scientists use the geological time scale to divide Earth’s overall history into a number of major segments. Just as humans think of periods like the Middle Ages and the Renaissance, scientists divide the geological history of the Earth into supereons, eons, eras, and periods such as the Precambrian supereon, the Mesozoic era, and the Paleogene period.
Geological history has been established with a number of techniques, many of which revolve around stratigraphy, the study of rock layers. In stratigraphy, geologists examine the layers of geological material that have been deposited over the eons, dating these layers with scientific techniques and using the dates to establish various critical points in time. Rock layers can also be used to track the movement of the Earth’s tectonic plates, the age of geological features such as mountains, and the overall age of landscapes.
The largest unit of time in geological history is the supereon. Each supereon is subdivided into a series of smaller aeons, divided into eras, periods, epochs, and then ages. Dating can get a little messy with geological history; unlike human history, where being off by 100 years makes a big difference, geological history deals with time spans so vast that 100 years is a trivial error. The goal is to provide an approximate timeline that geologists can use to establish a picture of events.
A number of useful things can be accomplished with the study of geological history. The ability to date various rock layers, for example, has allowed geologists to date the appearance of historical organisms. Paleobiology students use this information to determine when organisms first appeared and to seek information about major evolutionary changes, such as the first appearance of mammals. Paleobotany and paleoclimatology also use geological timescale information to determine what the Earth’s climate has been like at various points in history and for how long climate change has occurred.
Geologists are also interested in how the Earth formed and changed throughout geological history. Their studies have explored everything from periodic reversals of the magnetic poles to why some elements are rare and others abundant.
There are occasional disputes about geological history. Inaccurate dating has led to challenges about various findings and beliefs, and sometimes not enough information is available to draw clear, incontrovertible conclusions. As with other sciences, geology’s goal is to gather information dispassionately, contributing to general knowledge of the world, and geological history can sometimes include contradictions or evidence that challenges some conclusions and beliefs.
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