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The Geologic Time Scale and a Brief History of Life on Earth - Online Term Paper

The Geologic Time Scale and a Brief History of Life on Earth

Handout for GLY 137 - The Dinosaurs

The Geologic Time Scale and a Brief History of Life on Earth

The Geologic Time Scale is divided into four major units: Eons, Eras, Periods and Epochs. An Eon is the longest division of geologic time, so long in fact that there have only been four Eons. Collectively the first three eons are called the Precambrian, that stretch of geological time from the formation of the Earth itself to the start of the Cambrian period. This immensely long stretch of time - some four billion years or more - saw the formation of the Earth as a planetary body, including geosphere, atmosphere, and hydrosphere, as well as the appearance of life.

Divisions of the ...

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time, the Solar System was forming, probably within a large cloud of gas and dust around the sun, called an accretion disc. The sun formed within such a cloud of gas and dust, shrinking in on itself by gravitational compaction until it began to undergo nuclear fusion and give off light and heat. Surrounding particles began to coalesce by gravity into larger lumps, or planetesimals, which continued to aggregate into planets. "Left-over" material formed asteroids and comets.

Because collisions between large planetesimals release a lot of heat, the Earth and other planets would have been molten at the beginning of their histories. Solidification of the molten material into rocks happened as the Earth cooled. The oldest meteorites and lunar rocks are about 4.5 billion years old, but the oldest Earth rocks currently known are 3.8 billion years old. Sometime during the first 800 million or so years of its history, the surface of the Earth changed from liquid to solid. Once solid ...

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produce oxygen as a by- product. Photosynthesis is the only major source of free oxygen gas in the atmosphere. As stromatolites became more common 2.5 billion years ago, they gradually changed the Earth's atmosphere from a carbon dioxide-rich mixture to the present-day oxygen-rich atmosphere. This major change paved the way for the next evolutionary step, the appearance of life based on the eukaryotic cell.

The period of Earth's history that began 2.5 billion years ago and ended 544 million years ago is known as the Proterozoic. Many of the most exciting events in the history of the Earth and of life occurred during the Proterozoic -- stable continents first appeared and began to ...

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PAPER DETAILS
Added: 9/24/2020 05:30:48 PM
Submitted By: 20200346
Category: Science & Nature
Type: Premium Paper
Words: 5987
Pages: 22

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