Smithsonian National Museum of Natural History Geologic Time The Story of a Changing Earth
Presented by the Department of Paleobiology.
The Hadean
Formation of the Earth
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Part of a meteorite that hit Arizona about 50,000 years ago.
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Approximate Dates: 4.6–4.0 bya
Defining Characteristics:
  • • formation of Earth’s crust and main bombardment
Secondary Characteristics:
  • • continuing erosion and plate tectonics have destroyed Hadean rocks

The name Hadean Eon comes from Hades, the underworld of Greek mythology. It refers to the “hellish” conditions of the Earth during the earliest part of its history, when much of the Earth’s surface remained molten. The Hadean Eon of geologic time began with the birth of the solar system, including our planet, Earth, and ended with the formation of the oldest rocks that are still preserved on the surface of Earth.

The Hadean is the first period in Earth history, but one for which we have little record. The Earth began to form about 4.6 billion years ago through the condensation of material around the sun. As this material collected, further cosmic material was drawn to it by gravity from all directions, increasing the size of the Earth. This process created an enormous amount of heat, which melted these materials and eventually allowed them to separate into different layers. As the Earth cooled, it acquired the structure we know today—an iron core, silicate mantle, and thin outer crust.

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