PHANEROZOIC EON: CHARACTERISTICS, LIFE, GEOLOGY, DIVISIONS - GEOGRAFÍA - 2025

The Phanerozoic Aeon is a geological time scale that is located after the Proterozoic, which belongs to the Precambrian. It is perhaps the most interesting geological stage and the one with the most fossil records. There are many experts in paleontology who have dedicated themselves to elucidating the mysteries that this eon keeps.

During this eon, events that are considered milestones in the study of the history of planet Earth occurred. These include: the formation and fragmentation of the supercontinent Pangea, the origin and extinction of the dinosaurs, the flourishing of a great variety of life forms (including man), two massive extinction processes and ice ages.

Representation of the Phanerozoic Period. Source: Mauricio Antón, via Wikimedia Commons

The importance of this eon lies in the fact that the planet became a place capable of welcoming and allowing the development of life, to the extent that it acquired the characteristics that it still retains today.

characteristics

Duration

The Phanerozoic Aeon spans 542 million years ago to the present day.

The atmosphere and oxygen

During this era, the atmosphere was acquiring more and more oxygen, a product of photosynthesis by photosynthetic organisms, such as blue-green algae, and later, the plants that are known today.

In the previous eon, the Proterozoic, blue green algae had made their appearance and began the process of releasing oxygen into the atmosphere, which was fixed through various processes. However, there came a point where these were insufficient and molecular oxygen began to accumulate in the atmosphere.

Thus, during this eon, atmospheric molecular oxygen reached concentrations similar to those it currently has.

A mass extinction of living things occurs

The most massive extinction on record occurred in the Phanerozoic Aeon. It was so catastrophic that it is estimated that only 5% of the species that existed until that moment survived.

However, this process has been very difficult to study, as there are drawbacks and inconsistencies among those who have dedicated themselves to studying it.

The supercontinent known as Pangea was formed

Due to a series of displacements and movements that the existing continents underwent at that time, a supercontinent was formed which the experts baptized with the name of Pangea.

Of course, this was a gradual process that took place over billions of years. Likewise, as is well known, Pangea did not stay together, but later underwent fragmentation to form the continents that are known today.

All these events were masterfully described by the German geophysicist Alfred Wagner, who in 1912 proposed the Theory of Continental Drift.

geology

From the geological point of view, two very important things happened in the Phanerozoic Aeon: formation and subsequent fragmentation of Pangea and the so-called orogenies.

Orogenies

Orogeny is the part of geology that specializes in the formation of mountains. During this era and thanks to the movement of the different plates that make up the earth's crust, very important orogenic processes took place that contributed to the creation of the mountain ranges that are known today.

In this eon, there were three main orogenies, two of which occurred during the Paleozoic. These orogenies were: Caledonian orogeny, Hercynian orogeny and the Alpine orogeny.

Caledonian Orogeny

This process was carried out in what is now the northwest of the European continent, where the United Kingdom, Ireland, Wales, western Norway and eastern North America are located.

The main event was the collision of several plates that were located in the aforementioned areas. The vestiges that remain of this are located mainly in Scotland and the Scandinavian Peninsula.

As a result of these plate collisions, a supercontinent called Laurasia was formed.

Hercynian Orogeny

It lasted approximately 100 million years. The protagonists of the collision were the newly formed Laurasia and Gondwana. According to various records and according to the opinion of experts in the area, in the place where both continents collided, mountain ranges similar to the Himalayas must have formed.

Long-term consequences of the Hercynian orogeny include the Swiss Alps and the Himalayas. Similarly, the movement of the North American and South American plates to the west gave rise to two important and recognized mountain ranges in the American continent: the Andes Mountains in South America and the Rockies.

Alpine Orogeny

It was a very significant process that resulted in the formation of the southern mountain ranges of the European and Asian continents.

In the Lower Cretaceous period, the Eurasian, Indo-Australian and African plates began to experience a pattern of convergent movements until they collided, giving rise to the following mountain ranges: Atlas, Carpathian Mountains, Caucasus, Apennines, Alps, Himalayas and Hindu Kush, among others..

Himalayan mountain range, formed during this eon. Source: NASA, via Wikimedia Commons

Another important event during this era is that thanks to the movements of the earth's crust, the Red Sea originated.

Formation and fragmentation of the Pangea

During the Phanerozoic Eon, the supercontinent Pangea was formed, which was a very important geological fact for which there is evidence.

Genesis of the Pangea

As in any geological process, Pangea was formed over billions of years, in which the different fragments that finally formed it were moving through the existing oceans until they collided with each other.

The first steps go back to the Cambrian era, in which Laurentia (continent) began its movement towards the south pole. Likewise, there were other changes with other continents. For example, Laurentia, Avalonia, and Baltica were united, and formed one known as Euramérica.

Later, this continent collided with the so-called Gondwana. The southeastern coast of Euramerica then collided with the northwestern edge of Africa. Finally, the rest of the fragments collided with the great mass of the Earth's crust to finally form the supercontinent already mentioned.

It is important to note that the product of all these movements formed many of the mountain ranges that are known today as the Mauritanians or the Appalachians.

End of Pangea

One of the foundations of the Continental Drift Theory is that the great land masses are in continuous movement.

Due to this, thousands of years after it was formed, Pangea began to experience a fragmentation process that gave rise to the continents as they are known today. This process began during the Mesozoic era and continues to this day.

The first separation that occurred was that of North America from Africa. Later, about 150 million years ago, the second separation took place: the Gonndwana continent was fragmented into several pieces, which correspond to South America, India, Antarctica, Africa and Australia.

Finally, in the early Cenozoic, North America and Greenland separated and Australia separated from Antarctica. It is important to mention that as these great masses of land were displaced, the oceans that exist today were also formed, such as the Atlantic and Indian Oceans.

Weather

The Phanerozoic Aeon was a time of great climatic changes. This was largely due to the great variations that occurred at the level of the earth's crust and to the concentrations of various gases in the atmosphere, such as carbon dioxide (CO ₂).

For example, the fragmentation of Pangea and the displacement of the continents resulted in a variation in ocean currents, which in turn had a direct impact on climatic conditions.

During the Phanerozoic, there were both hot and very cold climates, so much so that there were two major glaciations.

At first, the climate was arid. However, thanks to the breakup of Pangea, that climate changed to one of humid and warm characteristics. The rise in temperature was maintained, and there was even a six degree rise in a short period of time.

Unfortunately, these conditions did not remain so, but with the formation of the polar cap in Antarctica, an ice age began. This decrease in temperatures on the planet led to the famous ice ages of the Quaternary period. These were periods when a large number of animals became extinct.

Finally, the climate has stabilized relatively, since the planet has not experienced glaciations again, but certain periods in which, in certain regions, temperatures have dropped more than normal. Fortunately, these events have not had the catastrophic consequences of the ancient ice ages.

Lifetime

The Phanerozoic Aeon was characterized by the flourishing of life. During this time, the planet, which had been preparing in earlier times, finally became a favorable place for a large number of life forms to flourish on it, many of which still persist.

The fossil record indicates that one of the first organisms to develop, and perhaps the most characteristic of the Paleozoic, were the trilobites, which were non-articulated, shelled animals.

Likewise, during this same period other invertebrates such as insects appeared. In the botanical area there were also events, as the first plants such as ferns appeared.

Trilobite fossil. Source: Pixabay.com

Later came the "Age of Dinosaurs" (Mesozoic). The warm climate here allowed both reptiles and dinosaurs to thrive. Similarly, some mammals and birds appeared. Plants with seeds began to appear and finally plants with flowers and fruits.

After the mass extinction of the dinosaurs, mammals and birds began to proliferate and diversify. Trees that are known today appeared and plants of gymnosperm types began to dominate. A very important advance was the evolution of primates, which triggered the appearance of Homo sapiens sapiens, modern man.

Subdivisions

The Phanerozoic Aeon is divided into three major eras: Paleozoic, Mesozoic, and Cenozoic.

Paleozoic

It had its beginning approximately 541 million years ago and culminated 252 million years ago. This era was characterized by the great flourishing of life, both in the seas and on the land surface.

During this era several of the geological phenomena took place that ended with the formation of the supercontinent Pangea. Likewise, animals evolved from small trilobites to reptiles.

At the end of this era, the most massive extinction process that the planet has experienced occurred, in which almost 75% of the species known at that time disappeared.

Mesozoic

It was known as the "Age of Reptiles." It spanned from 245 million years ago to 65 million years ago.

During this era the climate was quite stable, being hot and humid. These characteristics allowed more complex life forms such as vertebrates to develop, among which reptiles predominated.

Similarly, in this era the fragmentation of Pangea occurred and in the end, another extinction occurred in which about 70% of the species that inhabited the planet died.

Cenozoic

It had its beginnings 66 million years ago and continues to the present day.

During this era, mammals, both marine and terrestrial, developed and diversified, with a large number of new species appearing.

In this era the planet went through a kind of nuclear winter, in which there was practically no sunlight and there were very low temperatures.

References

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