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An overview of the pre achaean achaean and proterozoic eras

The atmosphere was very different from what we breathe today; at that time, it was likely a reducing atmosphere of methane, ammonia, and other gases which would be toxic to most life on our planet today.

Also during this time, the Earth's crust cooled enough that rocks and continental plates began to form. It was early in the Archean that life first appeared on Earth. Our oldest fossils date to roughly 3.

In fact, all life during the more than one billion years of the Archean was bacterial. The Archean coast was home to mounded colonies of photosynthetic bacteria called stromatolites. Stromatolites have been found as fossils in early Archean rocks of South Africa and western Australia. Stromatolites increased in abundance throughout the Archean, but began to decline during the Proterozoic.

They are not common today, but they are doing well in Shark Bay, Australia see photo below.

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The Hadean Hadean time 4. No rocks on the Earth are this old, except for meteorites. During Hadean time, the Solar System was forming, probably within a large cloud of gas and dust around the sun, called an accretion disc. Heavier elements are generated within stars by nuclear fusion of hydrogen, and are otherwise uncommon.

We can see similar processes taking place today in so-called diffuse nebulae in this and other galaxies, such as the Nebula M16, below left. Asteroid Ida and its moon as imaged by the Galileo spacecraft in 1993. The spacecraft was about 10,500 kilometers 6,500 miles from the asteroid. 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.

An overview of the pre achaean achaean and proterozoic eras

Surrounding particles began to coalesce by gravity into larger lumps, or planetesimals, which continued to aggregate into planets. 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 rock happened as the Earth cooled. The oldest meteorites and lunar rocks are about 4. Sometime during the first 800 million or so years of its history, the surface of the Earth changed from liquid to solid.

  • Find out more about the Precambrian paleontology and geology of North America at the Paleontology Portal;
  • The period of earth's history that began 25 billion years ago and ended 5420 million years ago is known as the proterozoic, which is subdivided into three eras;
  • The war against nabis the achaean leagueball, pergamonball and macedonball pre-world war i era 1910 - 1913;
  • The hellenistic period is a part of the ancient period this period is not an intermediary era between the prosperous the achaean league and antigonos iii of;
  • In fact, all life during the more than one billion years of the Archean was bacterial;
  • Asteroid Ida and its moon as imaged by the Galileo spacecraft in 1993.

Once solid rock formed on the Earth, its geological history began. This most likely happened prior to 3. Erosion and plate tectonics has probably destroyed all of the solid rocks that were older than 3.

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The advent of a rock record roughly marks the beginning of the Archean eon. Resources and references Bengtson, S. Early Life on Earth. Columbia University Press, New York.

Its Origin and Evolution. Princeton University Press, Princeton. Read more about Shark Bay and its stromatolites or stromatolites in general on Wikipedia.

Learn more about the Archean and Hadean on Wikipedia. Find out more about the Precambrian paleontology and geology of North America at the Paleontology Portal.