ARCHAIC AEON: CHARACTERISTICS, LIFE, GEOLOGY AND SUBDIVISIONS - GEOGRAPHY - 2025

The Archaic eon was one of the first geological eras of the planet, belonging to the Precambrian, preceded only by the Hadic eon. It had its beginnings about 4 billion years ago and spanned the time when the Earth was still developing its characteristics as a habitable planet.

It was one of the longest geological eras, encompassing almost a third of Earth's total life. The word Archaic comes from a Greek word that means origin. There is no better name for this geological age, as it represented the point of origin of life on the planet.

Dolomeu Crater, Reunion Island, similar in appearance to the Archaic eon.

During the early Archaic era, terrestrial conditions were very hostile, the ambient temperature was extremely high, and there was intense volcanic activity.

Likewise, the atmosphere was loaded with gases, which greatly hindered the development of some form of life. On the other hand, the earth's crust was not completely stable, therefore the tectonic plates were just forming.

However, thanks to various processes that today have been verified and established at an experimental level, the first forms of life began to appear, very primitive and simple in its beginnings, but which constituted the starting point for future development and evolution. in more complex ways than are currently known.

General characteristics

Duration

The Archaic aeon lasted approximately 1500 million years, divided into four subdivisions. It began 4 billion years ago and ended 2.5 billion years ago.

It was turbulent

The Archaic eon was characterized because the conditions of the planet were turbulent, there was no stability (at least in its beginnings) and the climatic conditions were hostile.

There was intense volcanic activity, as well as a constant emanation of atmospheric gases. All this caused that the environmental temperature was quite high, making the development of life difficult.

Appearance of the first forms of life

During this era, the first living beings that populated the planet appeared, these being prokaryotic unicellular organisms, which were conditioned to survive in the prevailing adverse conditions.

However, as atmospheric and environmental conditions stabilized, life forms diversified.

geology

So far, the oldest rocks that are known come from the Archaic era. There are several sites where rocks from this era have been found. These include: Greenland, Canada, India, Brazil, and South Africa, among others.

During the Archaic eon great changes occurred at the geological level. There were folding and formation of supercontinents like Pannotia.

The rocks that have been recovered from this era, present igneous strata, as well as metamorphic sedimentary. Likewise, certain fossils have been found in the rocks that come from forms of marine life, such as algae and some bacteria.

Similarly, volcanic sediments have been found, as well as banded iron rocks, which have served as an aid to elucidate the great geological changes that occurred during the Archaic era.

During this era, the supercontinent Pannotia eventually divided into four pieces of land: Gondwana, Baltica, Laurentia, and Siberia. In later ages these pieces of land came together again to form another supercontinent: the Pangea.

Lifetime

According to specialists in the area, life began in the Archaic eon. At the beginning of this eon, the conditions of the Earth did not allow the development of life, but later those conditions changed and it was possible that the first living beings appeared.

It was a time when life was practically non-existent, taking into account environmental characteristics. The primitive atmosphere was not suitable for the development of life as it is known today.

There are various theories that try to explain how the first life forms emerged. One of the most accepted is the one that has to do with the Oparín coacervate hypothesis, supported by the Miller and Urey experiment.

Oparín coacervate hypothesis and Miller and Urey experiment

These hypotheses suggest that the primitive atmosphere was made up of ammonia, water, methane and hydrogen. Likewise, it is believed that in the primitive atmosphere there were a large amount of electrical discharges from lightning and thunder, as well as high temperatures.

Taking this into account, it was suggested that thanks to the electrical discharges and high temperatures, these gases reacted and formed the so-called coacervates, which were structures enclosed by a membrane that contained organic molecules, such as some amino acids.

It is known that amino acids are organic compounds that make up proteins and that these in turn make up living beings. In such a way that the first step for life to develop was the formation of these organic compounds, which in one way or another evolved to form the first living being: a unicellular prokaryotic organism.

Diagram of the Miller-Urey experiment. Source: GYassineMrabetTalk✉ / Translation: Elisardojm This W3C-unspecified vector image was created with Inkscape., via Wikimedia Commons

This hypothesis was recreated in the laboratory at an experimental level by two scientists: Stanley Miller (an undergraduate student at that time) and Harold Urey, obtaining a large amount of organic compounds that could well be the precursors of life.

First forms of life

As mentioned, the first life forms to appear on Earth were prokaryotic unicellular organisms.

The oldest fossils found to date are blue-green algae, which is why it is believed that they were the first living things on the planet.

Likewise, the so-called stromatolites appeared, which are the result of the fixation of calcium carbonate by cyanobacteria.

Stromatolites have represented a great help for specialists, since they constitute environmental indicators, allowing to predict possible atmospheric conditions at a given time. This is because stromatolites develop under specific environmental conditions.

As time progressed, life forms specialized in various processes such as photosynthesis. At this point it is important to clarify that the first photosynthetic organisms carried out anoxygenic photosynthesis, that is, they did not generate oxygen in the atmosphere.

It was not until millions of years later that, through the evolution of existing living beings, the first organisms that were capable of photosynthesis as it is known today appeared, being possible to expel oxygen into the atmosphere.

In the same way, the existing living beings continued their evolution and the unicellular ones began to group until they gave rise to the first multicellular organisms (made up of more than one cell).

The first multicellular animals were soft-bodied and some have even remained until today (such as jellyfish).

Regarding the botanical part, in this era there were no large plants or trees. The members of the plantae kingdom of which there are fossil records were small mosses and lichens.

The greatest exponents of the group of plants appeared millions of years later, in the Paleozoic era. As far as is known, in the Archaic era, the continents were vast expanses of arid, desert land with no significant plant forms on them.

Weather

At first, the Earth's climate during the Archaic era was not friendly. This means that the conditions did not exist for life to develop.

According to the fossil records that have been obtained, as well as the conjectures made by experts on the subject, the climatic conditions were quite hostile.

It is believed that in the primitive atmosphere there was a great concentration of greenhouse gases, the product of various activities such as volcanism.

This caused the temperatures to be very high. In the atmosphere there were some gases such as methane, ammonia and hydrogen. Free oxygen was not available.

Over time, the atmosphere cooled, the elements in the gaseous state cooled to such an extent that they became liquid and later solidified, forming the first rocks.

As time progressed, the atmosphere stopped having high temperatures, making possible the development of life in it. The temperature reached a point very similar to what the Earth has today.

Subdivisions

The Archaic era was divided into four eras: Eoarchic, Paleoarchic, Mesoarchic, and Neoarchic.

Eoarchic

It lasted 400 million years. It was the first subdivision of the Archaic era. It was a time of instability in the earth's crust, since despite the fact that many areas were already solidified and were land, there were also others in which there was only lava.

Similarly, there are records that the first life forms (prokaryotes) date from this era. In addition, specialists suggest that during this time the Earth was subjected to intense activity from asteroids from outer space.

Paleoarchic

Like the Eoarchic, the Paleoarchic lasted approximately 400 million years.

The first fossils of life forms come from this era, such as some bacteria and there are even records that during this time stromatolites began to form.

Likewise, some bacteria evolved and began to carry out the photosynthesis process in their anoxygenic variant.

An important geological event was the formation of the first supercontinent, known as Vaalbará.

Mesoarchic

It also lasted approximately 400 million years. During this era, it is believed that a destabilization of the climate occurred thanks to the gases released into the atmosphere by living beings.

Likewise, some time later, the climate stabilized to a certain extent, reaching temperatures similar to current ones, thus allowing more forms of living beings to flourish.

In the same way, during this era the supercontinent Vaalbará was fragmented, giving rise to various fragments of land that much later in time were united in the Pangea. The stromatolites continued to expand and form.

It is believed that during this period the waters of the planet had a high content of iron, so they must have had a greenish color, and the sky, due to the high content of atmospheric carbon dioxide, would have a reddish hue.

The first glaciation of which there is record also occurred in this era.

Neoarchic

It is the last subdivision of the Archaic era. It lasted approximately 300 million years.

The most important event that happened during this era was the improvement of photosynthesis as a metabolic process, going from anoxygenic to oxygenic.

Thanks to this, large amounts of oxygen passed into the atmosphere, which negatively affected some living organisms, since oxygen was harmful to them. This would result in the following was the so-called "Great Oxidation."

References

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