Geologic Time

Humans divide time into different divisions. A decade is equal to ten years, a century is equal to one hundred years, and a millennium is equal to one thousand years. All of these lengths of time are not adequate when trying to separate Earth’s history. A paleontologist is a geologist who studies prehistoric life, and paleontologists have created four separate divisions of geologic time. When studying the scale of geologic time, you may encounter a common abbreviation: MYA. MYA stands for million years ago.

Geologic Time Divisions

The geologic time scale is arranged to show the most recent geologic events at the top and the oldest events are found at the bottom. At the top of the scale, you find the divisions eon, era, period, and epoch. These are units of time designed by geologists to help organize all of Earth’s history. The units are arranged in order, from left to right, from the longest to the shortest periods of time. These divisions are created based on events that are observed with fossils or other pieces of crucial evidence. Click the player button to begin.

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A Tour of Geologic Time

The geologic time scale holds secrets to the life that has existed on Earth since the beginning of time. In this interactivity, select the different areas of the geologic time scale to view more information about their characteristics. Make sure to view each segment. Click the player button to begin.

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Mass Extinctions

Of all the life-forms that have ever lived on Earth, both plant and animal, almost 90% are extinct. The term "extinct" means that the organism and its species no longer exist. The most well-known extinction event occurred at the end of the Cretaceous period. Dinosaurs roamed the Earth for 186 million years and they are now extinct. There are no dinosaur fossils in any rocks younger than 65 million years old. Scientists believe that a large meteor impacted the Earth near the Yucatan Peninsula in the Gulf of Mexico. This massive impact caused tremendous amounts of dirt, rock, and debris to enter the atmosphere and led to the extinction of all the dinosaurs. In addition to dinosaurs, many other species present on the surface also went extinct. Events where massive natural disasters cause numerous species to become extinct are called mass extinctions. There have been four major mass extinction events discovered by paleontologists. These extinctions cause one division of geologic time to end, thus beginning another division.

Geologic Time Review

Now that you have investigated geologic time, practice what you have learned. In this non-graded interactivity, read each statement and decide if it is true or false. Click the player button to get started.