People have been studying earth and rock formations for a very long time.

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The next layer may have been chunky conglomerate rock, while the next was a layer of shale and fish fossils.

Geologists called these layers of different rock types strata. Minutes are fine for measuring daily chores, like driving to an appointment, fixing dinner, or doing the laundry.

They studied rock strata all around the world in order to figure out major events in geologic history. But what if you're talking about a bigger chore, like training for a marathon? And when we look at human history, we talk about it in terms of hundreds and thousands of years.

To answer these questions, geologists use a special timeline called the Geologic Time Scale.

It's a record of the earth's geologic history as scientists have come to understand it by studying the layers in rock.

The geologic time scale is broken up into larger and smaller subdivisions, which help us get a better sense of how historical events fit together.So, in this lesson, we're going to learn how the time scale was created and how its major subdivisions fit together to tell the story of Earth's history.Abstract: Biochronology attempts to rank, order and scale fossil events and fossil ranges in linear time, and scale regional stratigraphies with isochrons.Quantitative stratigraphic methods assist to construct biochronologies that underpin the geologic time scale.The geologic time scale is an essential tool for understanding the history of Earth and the evolution of life.In this lesson, explore the principal eons, eras, periods, and epochs that help us track major events in geologic history. How do we know when birds first appeared on Earth or when humans evolved? How was our planet formed and populated by living things over time?