We explain what the archaic eon was, the stages into which it is divided and its characteristics. Also, what was the emergence of the first forms of life and the oceans.
During the Archean eon, the first evolution of the Earth’s crust occurred.
What was the Archean eon?
The Archaic is the second geological period that integrates the so-called precambrian eon. It is estimated that it began 3.8 billion years ago., once the Earth was formed in its most primitive geological and atmospheric stages. It ended about 2.5 billion years ago, with the beginning of the Proterozoic eon.
Name Archaic comes from Greek archewhich means “origin, beginning”It was a significant period in the early formation of the planet, as primitive life emerged and the first evolution of the Earth’s crust took place.
This 1.3 billion year period of time is subdivided into three eras: the Early Archean, the Middle Archean and the Late Archean. It is also the eon in which the first continents began to formas the crust begins to cool and solidify.
In some classifications, the Archean is considered the first geological period within the Precambrian eon and the events of the Hadic or Azoic eon are included there. This is because the difficulties in studying these very remote times do not allow us to determine exactly when one period ends and another begins.
Characteristics of the Archean Eon
The main characteristics of the archaic eon are:
- It began 3.8 billion years ago and ended 2.5 billion years ago.
- It is divided into three eras: the Early Archaic, the Middle Archaic and the Late Archaic.
- The crust begins to solidify and continents begin to form.
- The waters of the planet expand and the oceans extend.
- The first forms of life begin to appear on Earth.
- The atmosphere has a very low concentration of oxygen.
Division of the archaic aeon
The Archean eon is divided into three eras:
- Archaic initialIt began 3.8 billion years ago and ended 3.4 billion years ago.
- Middle ArchaicIt began 3.4 billion years ago and ended 3 billion years ago.
- Late Archaic. It started 3 billion years ago and ended 2.5 billion years ago.
Geology of the Archean Eon
Volcanic and tectonic activity may have destroyed more than one continent.
The main geological characteristic of the archaic eon is that the formation of the first continents takes placeAlthough it is a topic that is still under debate, the most accepted hypotheses maintain that there were smaller continents than those today, and that they moved, enlarged and were destroyed over the course of geological time.
The latter is due to the fact that the planet’s heat flow towards its crust was much greater than the current one, which increased the movements of the lithosphere (the most solid and superficial layer of the Earth), and allowed the creation of small plates that They changed shape and size.
Thus, there were no large continents on the planet during the Archeanbut rather protocontinents that were constantly separating and colliding.
Among the rocks generated during this period are plutonic masses of granite, dorite, anorthosite and monzonite.
The supercontinent of Vaalbará
Vaalbará is believed to have formed from two cratons called Kaapvaal and Pilbara.
Vaalbara is a hypothetical first supercontinent that would have formed during the early Archean era.between 3.8 and 3.6 billion years ago. It is believed to have broken up 2.8 billion years ago.
The most accepted hypothesis maintains that Vaalbará was formed from two archaic cratons (areas of the crust formed by the oldest rocks on the planet), called Kaapvaal (part of present-day South Africa) and Pilbara (part of present-day Australia). This is inferred from the geological similarities between these two regions, which are currently so far apart.
The formation of the oceans
Towards the end of the Archean eon, large accumulations of water (which later formed the oceans) reached more or less 50% of the surface they occupy today.. Its formation was continuous, and as volcanic activity expelled water vapor into the atmosphere, which was then precipitated in liquid form, the surface of the oceans increased.
Water also flowed from deep ocean basins, in which there was an abundant presence of iron that, unable to oxidize, dissolved. This element was very abundant and is believed to have played a fundamental role in the emergence of life.
Archean Eon Climate
For much of the early eon, Earth’s atmosphere was composed primarily of gases such as carbon dioxide, methane, and water vapor.. Thus, the concentration of oxygen in the atmosphere was low compared to current levels.
Carbon dioxide and methane, which were very abundant during this period, are greenhouse gases. Their high concentration in the atmosphere produced surface temperatures significantly higher than today.
Despite this, there were occasional periods of cooling due to massive volcanic events that released large amounts of particulate matter, ash and aerosols into the atmosphere. It is thought that this may have caused less solar energy to reach the surface and lead to significant climate fluctuations.
The first forms of life
There is evidence of the presence of prokaryotic organisms known as cyanobacteria during the Archean eon. These single-celled organisms capable of fixing chemical elements to obtain energy have lived on the planet for at least 3.5 billion years.
The first fossils are of bacterial origin (archaebacteria). These early prokaryotic life forms performed anoxygenic photosynthesis, meaning they did not release oxygen into the atmosphere.
However, during the Archean eon, These organisms evolved and began to carry out the process of photosynthesis. In this way, oxygen began to be produced, which will substantially transform the atmosphere and impact the development of other forms of life on Earth.
Stromatolites
Stromatolites are mineral structures of biological origin.
Stromatolites are the first evidence of biological origin that exists on the planetThey are mineral structures, of diverse shape, whose origin is in the capture and fixation of carbonate particles by the first and primitive forms of life.
This means that the cyanobacteria of the Archean eon carried out a photosynthesis that captured carbon from the CO2 abundant in the atmosphere. With it, they formed carbonates that accumulated and sedimented, and thus were formed small rock constructions that remain to this day.
There are fossil stromatolites from almost all geological eras, and they are the oldest evidence of life on the planet. Those from the archaic eon are found in the Warrawoona region, in Australia.
References
- Casals, C. (nd). Archean Eon. Network Meteorology. https://www.meteorologiaenred.com/
- The Sieve. (2013). The biography of life 06. We enter the Archaic eon. https://eltamiz.com/elcedazo/
- Tarbuck, E. and Lutgens, F. (2005). Earth sciences. An Introduction to Physical Geology. Pearson Education.
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