PRECAMBRIAN ERA: CHARACTERISTICS, PERIODS, FLORA AND FAUNA - GEOGRAFÍA - 2024

The Precambrian Era is one of the periods into which the geological timescale has been divided. In general, it is considered to be the first stage in Earth's history. It began when the planet was formed, about 4.6 billion years ago, and lasted until 570 million years ago, making it the longest stage in history.

However, it should be noted that some scientists reduce its duration. Some authors call Azoic the period from the formation of the planet to 3.8 billion years ago, when, according to this current, the Precambrian began.

Stony sea. By Ghedoghedo, from Wikimedia Commons

The Precambrian is divided into three different eons (subdivisions), which serve to delimit the different geological and developmental events of the planet.

For a long time, the newly formed planet Earth suffered from environmental conditions that made any life impossible. Most of the gases in the early atmosphere were poisonous and volcanic activity was constant.

Over time, the planet gradually stabilized. The first bacteria appeared, releasing oxygen into the atmosphere. The terrestrial plate was also formed and life, initially very basic, began to flourish.

characteristics

The term Precambrian comes from the union of the Latin prefix "pre" (before) and Cambrian (from Cambria). This geological era is the longest in Earth's history. Scientists mark its beginning about 4.6 billion years ago and its end about 570 million years ago.

Despite its duration, it is not easy to study many of its characteristics. The very conditions of the planet at that time caused that many remains have not been preserved. Fossils, for example, are really rare. Only in an exceptional way are some belonging to the first organisms that inhabited the Earth.

As a representation, scholars often describe the planet surrounded by a dark sky, as the debris from the volcanoes blocked the sunlight. The storms were almost constant, with a lot of electricity.

The rain, for its part, evaporated as soon as it touched the ground, very hot due to thermal activity. This released large amounts of vapor into the early atmosphere, made up of various poisonous gases.

Planet formation

The most widely accepted hypothesis today is that the Earth formed about 4.6 billion years ago. The creation of the planet occurred from clouds of dust and gases that were accumulating. The dust began to melt and turn into rocks.

At that time, the atmosphere surrounding the Earth was made up of methane and hydrogen, both incompatible with life.

Somewhat later, volcanic activity began to expel carbon dioxide and water vapor. Over time, the Earth cooled down and this vapor was transformed into liquid water and, finally, to form seas and oceans. It would be there where the first forms of life would appear.

Similarly, it was at that time that the lithosphere, hydrosphere, and atmosphere were formed.

Environmental conditions

Volcanoes played a very important role in the early part of the Precambrian. The water vapor they expelled, along with carbon dioxide, formed the basis of the proto-atmosphere. What did not yet exist was oxygen.

When the planet's temperature dropped below 100 ° C, about 3.8 billion years ago, the first rocks solidified. Similarly, there is evidence that the first ocean appeared, which accumulated salts.

Eventually, the cooling led to the earth's crust stabilizing, becoming thicker and stiffer. The same happened with the atmosphere, in which ammonia, methane or hydrogen sulfide disappeared. In their place, nitrogen and oxygen appeared.

The climate also stabilized around 2.5 billion years ago, allowing some examples of life to appear. It would not be until 1800 million years ago when cyanobacteria were able to produce enough oxygen for its effects to begin to be noticed.

On the other hand, during the Precambrian there were different climatic periods, from the desert to some ice ages.

Periods (subdivisions)

The International Commission on Stratigraphy has divided the Precambrian into three different periods, or eons,.

Hadic or Hadean Aeon

The first part of the Precambrian is called Hadic or Hadean. The name comes from the Greek Hades, which was what the underworld was called in ancient Greece.

The Hadic began when the Earth was formed, about 4.6 billion years ago, and ended 4 billion years ago.

The Solar System, according to the most widely followed theories, was formed within a cloud of gas and dust. When some of that material, which was at very high temperatures, began to coalesce and cool down, planets were formed, including Earth.

It was then that the earth's crust appeared. For a long time, the crust was very unstable, as there was great volcanic activity.

Scholars have found some rocks in Canada and Australia that may have come from the Hadic Aeon, since they are dated about 4.4 billion years ago.

One of the most important cosmic events of the era occurred in that Aeon. This is known as the late intense bombardment, when a large number of meteorites ravaged the planet. The thin atmosphere of the time was no defense to fragments traveling through space.

Archaic Aeon

The second stage in which the Precambrian is divided is known as Archaic, although it was previously called Archaeozoic. It began 4 billion years ago and lasted about 1.5 billion, ending 2.5 billion years ago.

The earth's crust evolved during this period, indicating that there was considerable plate tectonics (plate movement) and an internal structure similar to today. In contrast, the temperature in said crust was much higher than today.

In the Archaic there was still no free oxygen in the atmosphere. However, experts think that its temperature should not have been very different from what it presents today.

The first oceans had already formed and it is very likely that life made its appearance. This life was limited to prokaryotic organisms.

A major change occurred 3.5 billion years ago. That's when the bacteria began to photosynthesize, albeit of a type that didn't give off oxygen.

For that, we would have to wait until about 2.8 billion years ago. The first organisms that did release oxygen appeared, especially cyanobacteria. This caused a great change that prompted the appearance of other somewhat more complex life forms.

Proterozoic Aeon

The name of this third Precambrian subdivision indicates its characteristics. Proterozoic comes from two Greek words, whose union means "to be alive early."

This eon spans from 2.5 billion years to 524 years ago, and life began to become more common on the planet. Stromatolites, mineral structures with some biological characteristics, trapped carbon dioxide from the atmosphere and released oxygen instead.

Geologically, the period is characterized by the formation of large continental masses. The name scientists know them by is "cratons." These masses would be the ones that would give way to the continental shelves.

The cratons moved over the warm mantle that still made up the earth's crust. Collisions were frequent, leading to the appearance of the first mountains. Over time, all the cratons came together in a single mass, forming a single large continent, Pangea 1.

These cratons separated and joined up to three times during the Proterozoic.

geology

Geology in the Precambrian went through great modifications. It was, in short, a planet still in the formation phase, so the changes were continuous.

The volcanic activity was almost constant, which ended up causing large amounts of carbon dioxide and water vapor to reach the proto-atmosphere. In turn, this led to a drop in temperature and the rocks to solidify.

The continental crust was born from the Earth's upper mantle. It was a slow appearance, since it took a time that oscillates between the 3800 and the 2800 million years old. At that time the basalts and andesites were formed.

Experts assume that this early continental crust contained large amounts of aluminum silicates. The name given to the areas where there was already crust is shields and they are the origin of the current continents. In the Precambrian, however, the land was warmer and more discontinuous than it is today.

Pangea

In the second half of the Precambrian, just before the Proterozoic began, the activity of plate tectonics was transformed. The collisions became more frequent, as well as the unions of several continental blocks. That was the origin of the primitive continents.

Since the movements of the plates did not stop, the continental blocks were expanding in size, giving rise to supercontinents. In cycles of about 500 million years, these plates got closer to each other and then moved away again, breaking up the fragments.

1100 million years ago, Pangea I was formed at a time when all the continental blocks were grouped into a single mass. The subsequent separation would give rise to the current continents.

Rocks

The oldest rocks geologists have found on the planet date to between 4.1 and 4.2 billion years. They are small remains of zircon, a mineral.

However, to measure the age of the Earth they have looked at some meteorites. According to studies, these were formed at the same time as the planet and have allowed the date to be established at about 4.6 billion years.

On the other hand, the most frequent types of rocks during the Precambrian were igneous and metamorphic. Africa and Greenland, where the oldest terrestrial rocks are found, have made it possible to study the geology of the time somewhat more in depth.

Flora

The first forms of life, very primary, appeared during the Precambrian. The problem that scientists find when studying the biology of that period is that there are hardly any fossil remains.

The harsh and changing environmental conditions and the modifications of the terrestrial structure make it very difficult to be able to provide data on the Precambrian flora.

Algae

The first organisms to appear on the planet were bacteria. These, obviously, do not fall within the plant genus, but they had some characteristic that is related to this type of life.

In this way, some microorganisms could release oxygen into the atmosphere. They carried out photosynthesis, something that today is reserved for flora.

Some authors have divided these microorganisms between the purely bacterial ones and others more similar to algae. These seconds would be the chloroplasts and would belong to the plant kingdom.

The blue algae themselves, which did photosynthesis and which appeared in this period, had a biology quite different from that of current plants.

Corycium enigmaticum

The oldest fossil remains ever found is an algae that is about 1.5 billion years old. As previously mentioned, the remains from that period are very scarce and, it is possible, that the living organisms themselves were not too many.

Among those that have been found, the most numerous are seaweed. Biologists agree that the appearance of plants capable of photosynthesis and pouring oxygen into the atmosphere must have been fundamental for the multiplication of life.

Fauna

As with flora, scientists have great difficulty in knowing which animals existed in the Precambrian. The former must have lacked solid skeletons, thus preventing them from fossilizing.

The first people

The first living organisms were very simple. It is thought that they were just a system wrapped by a membrane and capable of duplication.

Protobionts, the name by which these first inhabitants of the planet are known, appeared at least about 3.5 billion years ago. Evolution saw to it that those who were best adapted to the circumstances survived.

The structure of these microorganisms was very simple, with one cell containing all the genetic information.

Scientists do not rule out that some kind of even simpler previous life existed, but no proof has been found.

Cyanobacteria

One of the most abundant organisms was cyanobacteria. They are one of the few that were preserved in fossils, allowing them to be known quite well.

They were responsible, 2800 million years ago, for producing the oxygen that ended up accumulating in the atmosphere.

Soft Corals, Jellyfish and Annelids

Much later, about 670 million years ago, life in the seas and on the continental shores had multiplied. Corals appeared, similar to the current ones but less rigid, as well as jellyfish and other types of aquatic beings.

Ediacara fauna

Among aquatic animals, the so-called Ediacara fauna stands out due to its size. The first fossils were found on the hill of the same name, in Australia.

They appeared 670 million years ago and could measure, more or less, a meter. Its body was soft and is considered to be a primitive branch of later forms of animal life.

References

1. AstroMía. Geological history: the Precambrian. Obtained from astromia.com
2. Junta de Andalucía. Precambrian Period. Obtained from adic.juntadeandalucia.es
3. Geological Route. The Precambrian. Obtained from rutageologica.cl
4. Windley, Brian Frederick. Precambrian time. Retrieved from britannica.com
5. Doubilet, David; Hayes, Jennifer. Precambrian Time. Retrieved from nationalgeographic.com
6. Schaetzl, Randall. The Precambrian Era. Retrieved from geo.msu.edu
7. Bagley, Mary. Precambrian: Facts About the Beginning of Time. Retrieved from livescience.com