The Archean describes an early part of the Earth's early season, the so-called Precambrian. It began about four billion years ago and is divided by scientists into four phases, namely those of the Eoarchic, the Paleo-Archaic, the Meso-Archeic and the Neo-Archeic. The period of the archaic lasted about two and a half billion years and was replaced by the Paleoproterozoic. Thus, the Archean is the longest phase in the history of the earth.
Despite the temporal length of the archaic, the rocks from this period make up only a small part of the earth's surface today. This is stated by scientists with about twenty percent. The oldest minerals that are still found today and come from the Archean, are more than 4 billion year old zircons, which formed from today's undetectable metamorphic rocks as weathering remnants. Gneisses covering parts of the Canadian Shield and Greenland are also known from the time of the archaic, as well as sedimentary rocks, which were also found in these regions and dated to an age of about 3.8 billion years.
The fact that sedimentary rocks existed on Earth 3.8 billion years ago suggests that there must already have been free water during the archaic phase. At the same time, the zircons indicate that the earth had already been covered by a crust, the surface of the earth differing greatly from that existing today. How exactly this phase of today's shell construction of the earth developed, is still not explored. Conjecture suggests that in the Archaic there was a precipitation of liquid mass, which was heated to temperatures of up to 1200 ° C. This theory is corroborated by the fact that residual magnetism is detectable in the rocks originating from this phase, which means that the earth must have possessed a magnetic field at that time. Early mainland islands probably originated from the liquefied mass some three billion years ago, which gradually led to the formation of the first supercontinent Ur near the equator.
Flora and fauna:
Even though the Earth's atmosphere did not contain any free oxygen at the time of the early archaic, findings from chemofossils suggest that living things already colonized the Earth in the paleoarchic. The scientists defined these as remnants of blue algae, or the algae attributed bacteria. It has been shown that some macromolecules have already developed the ability to reproduce or increase in size by combining with stable molecules of the Earth's structure. Traces of such chemofossils, which are visible as threads in the microscope, were discovered by scientists in small quantities in rocks that originate from today's South Africa and are about three and a half billion years old. Only through the photosynthesis of prokaryotes, cell-built, but coreless organisms, was given in the late Archean oxygen, which provided the basic prerequisite for the development of flora and fauna in subsequent phases of Earth's history.