PALEOZOIC ERA: CHARACTERISTICS, GEOLOGY, FLORA AND FAUNA - GEOGRAFÍA - 2025

The Paleozoic era is one of the three stages into which the Phanerozoic Aeon is divided. Etymologically speaking, Paleozoic comes from "Palaio", which means ancient, and from zoe, which is life. Therefore, its meaning is "old life".

Many specialists express that the Paleozoic era is a time of transition, between primitive organisms to more evolved organisms capable of conquering terrestrial habitats.

Paleozoic fossils. Source: Yinan Chen, via Wikimedia Commons

Multicellular organisms underwent a series of transformations that allowed them to adapt to the terrestrial environment, one of the most significant being the development of the amniote egg.

Definitely the Paleozoic era was a time of great changes on the planet, from every point of view: geological, biological and climatic. Throughout the period it lasted, changes occurred one after another, some of which are very well documented and others not so much.

General characteristics

Duration

The Paleozoic era spanned approx. 541 million years ago until approx. 252 million years. It lasted about 290 million years.

Life blast

During this era there was a great diversification of multicellular life forms, both marine and terrestrial. It was one of the times in which there was a greater diversity of living beings, increasingly specialized and even capable of leaving marine habitats and undertaking the conquest of terrestrial spaces.

Formation of the Pangea

At the end of this era, the supercontinent known as Pangea was formed, which would later divide to give rise to the continents that are known today.

Several glaciations and a mass extinction

Throughout the Paleozoic, the ambient temperature fluctuated. There were periods when it remained warm and humid, and others when it decreased markedly. So much so that several glaciations occurred.

Likewise, at the end of the era, environmental conditions became so hostile that a massive extinction event occurred, known as the Great Dying, in which approximately 95% of the species that inhabited the planet were lost.

geology

From a geological point of view, the Paleozoic era was fraught with great changes. The first major geological event to occur during this era is the separation of the supercontinent known as Pangea 1.

Pangea 1 separated into several continents, which gave the appearance of islands surrounded by shallow seas. These islands were the following: Laurentia, Gondwana and South America.

Despite this separation occurring, over the course of thousands of years, those islands came closer together and eventually a new supercontinent was formed: Pangea II.

Likewise, during this era two geological events of great importance for the relief of the planet occurred: the Caledonian Orogeny and the Hercynian Orogeny.

Caledonian Orogeny

This was a mountain-building process that occurred in the area where Ireland, Scotland, England, Wales, and part of Norway now sit.

During this process, several plates collided. As a consequence of this, Laurasia, a supercontinent, was formed.

Hercynian Orogeny

This was a process that was involved in the formation of the supercontinent Pangea. During this process, two large land masses, Laurasia and Gondwana, collided. Likewise, there was the displacement of other plates such as the South American and the North American.

As a result of these collisions, mountain systems with large peaks were created, which were later lost by the natural process of land erosion.

Geographical modifications

During the 300 million years that the Paleozoic era lasted, a series of geographical modifications took place in relation to the great extensions of land that existed at that time.

At the beginning of the Paleozoic era, a large number of these pieces of land were located around the Equator. Laurentia, Baltica, and Siberia were converging in the tropics. Subsequently, Laurentia began to move north.

In roughly the Silurian period, the continent known as Baltica joined Laurentia. The continent formed here became known as Laurasia.

A little later in time, in the Middle Paleozoic, the supercontinent Gondwana fragmented into several pieces of land, which moved towards the equatorial regions. Later they were reunited again to form the supercontinent Euramérica.

Finally, the supercontinents that would later originate the African continent and South America collided with Laurasia, forming a single land mass known as the Pangea.

Lifetime

The Paleozoic was characterized by an explosion of life rarely given during the ancient ages of the planet. Life developed in each and every one of the spaces that could be colonized: air and land.

During the more than 290 million years that this era lasted, the forms of life diversified in such a way that they were appreciated from tiny animals, to the large reptiles that became dinosaurs at the end of it.

The true explosion of life occurred at the beginning, during the Cambrian period, since it was there that the first multicellular organisms began to appear.

They first appeared in the water, to later gradually colonize the land through the development of structures that allowed them to withstand the arid and dry environment of terrestrial ecosystems.

Flora

The first forms of plants or plant-like organisms to be seen during the Paleozoic period were algae and fungi, which had developed in aquatic habitats.

Later, towards the next subdivision of the period, there is evidence that the first green plants began to appear, which thanks to their chlorophyll content began to carry out the photosynthesis process, being largely responsible for the oxygen content of the earth's atmosphere.

These plants were quite primitive, without conductive vessels, so they had to be in places with a wide availability of humidity.

Later the first vascular plants appeared. These are plants that contain conductive vessels (xylem and phloem) through which nutrients and water circulate that is absorbed through the roots. Later, the group of plants expanded and became more and more diversified.

Ferns, seed plants, as well as the first large trees appeared, with those belonging to the genus Archaeopteris having a place of honor, since they were the first true trees to appear. The first mosses also made their appearance during the Paleozoic.

This great diversity of plants remained that way until the end of the Permian, when the so-called "Great Dying" occurred, in which almost all the plant species that inhabited the planet at that time perished.

Fauna

For the fauna, the Paleozoic was also a period of many changes and transformations, because throughout the six subdivisions that comprise the era, the fauna was diversifying and transforming, from small organisms to large reptiles that began to dominate the terrestrial ecosystem.

At the beginning of the Paleozoic, the first animals that were observed were the so-called trilobites, some vertebrates, mollusks and chordates. There are also sponges and brachiopods.

Later, the groups of animals were diversifying even more. For example, the cephalopods with shells, bivalves (animals with two shells) and corals appeared. In the same way, during this era the first representatives of the Echinoderm phylum appeared.

During the Silurian, the first fish appeared. This group was represented by fish with jaws and fish without jaws. Similarly, specimens belonging to the group of myriapods appeared. Life on the seabed continued to flourish, coral reefs became more diverse.

Later, the first representatives of the group of insects began to appear. The sea began to be dominated by fish with jaws, the first sharks appeared, as well as the first amphibians that had not yet come out to conquer the terrestrial habitat.

Already in the second half of the era, winged insects and the first reptiles appeared. Life in the sea was more diverse than ever, with mollusks, echinoderms, brachiopods and amphibians.

Towards the end of the Paleozoic, fauna diversity reached its peak. Reptiles were already abundant on land, insects continued to evolve, and of course, life continued to thrive in the sea.

However, all of this came to an end with the Permian - Triassic Mass Extinction. During this, 96% of the species that populated the planet and that have just been described, disappeared completely.

Weather

Not many reliable records of what the climate must have been like from the early Paleozoic. However, the specialists argue that, because the seas were very extensive, the climate must have been temperate and oceanic.

The Lower Paleozoic came to an end with an ice age event in which temperatures dropped and large numbers of species died.

Later came a time of climatic stability, in which there was a hot and humid climate, with an atmosphere in which there was abundant availability of carbon dioxide.

As plants colonized terrestrial habitats, atmospheric oxygen was increasing, while carbon dioxide was decreasing.

As time progressed through the Paleozoic, the climatic conditions were changing. At the end of the Permian period, climatic conditions made life practically unsustainable.

Although it is not yet known what the reasons for these changes were (there are several hypotheses), what is known is that environmental conditions changed, and the temperature increased several degrees, warming the atmosphere.

Subdivisions

The Paleozoic era has six subdivisions: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian.

Cambrian

It was the first subdivision of the Paleozoic era. It had its beginnings approximately 541 million years ago.

This stage was characterized by the so-called "Cambrian Explosion". During this, a large number of multicellular organisms appeared on the planet's surface. Among these, perhaps the most important group was the chordates, to which vertebrates belong.

Likewise, during this stage atmospheric oxygen levels reached levels capable of sustaining life. All this thanks to photosynthesis.

Cambrian fossil. Source: I, Drow male

In the same way, arthropods with exoskeletons were developed, which provided them with defense against possible predators.

The climate during this stage was a bit more friendly, which contributed to the emergence and development of new life forms.

Ordovician

It began immediately after the Cambrian, about 485 million years ago. Interestingly, it began and ended with a mass extinction.

During this period, the sea reached the highest levels it has ever had. Likewise, many of the existing life forms evolved. Life developed almost entirely in the sea, except for some arthropods that ventured to colonize the terrestrial habitat.

The characteristic flora of this period was represented by some green algae and some small plants similar to liverworts. The average environmental temperature was somewhat high, ranging between 40 and 60 ° C.

At the end of this stage a massive extinction event occurred, surpassed only by the Permian - Triassic Great Dying.

Silurian

This was a period characterized by a warm and pleasant climate, in comparison with the glaciation that put an end to the Ordovician. This was of great help to promote the development and maintenance of life in marine ecosystems.

Among the groups of animals that underwent great development and evolution are fish. Both fish with jaws and those without jaws experienced growth in species numbers and populated the early oceans.

In terrestrial ecosystems, life was also making its way. The first vascular plant fossils belong to this period.

This period also had a small extinction event, known as the Lau Event.

Devonian

It began about 416 million years ago. During this period, the group of fish continued to diversify. Likewise, cartilaginous fish appeared and developed, constituting the ancestors of today's sharks and rays.

Similarly, the first amphibians appeared that began to breathe through a pulmonary system. Other types of animals such as sponges, corals, and mollusks also developed and evolved.

Plants also reached a new horizon, as they began to develop structures that allowed them to settle on land, away from wet and swampy areas. There are records of trees that could reach 30 meters in height.

The colonization of the terrestrial habitat was a landmark of this period. The first amphibians began to move towards land, as did some fish that began to develop certain structures to survive the hostile terrestrial environment.

The period culminated in an extinction event that mainly affected marine life. Fortunately, the forms of life that moved towards the terrestrial environment managed to survive and take hold more and more.

Carboniferous

In this period, an increase in atmospheric oxygen levels was observed, which according to specialists, resulted in an increase in size, both of vascular plants and of various animals that moved through the terrestrial environment.

Insects evolve and the first flying insects appeared, although the mechanisms by which they developed have not yet been fully clarified.

Likewise, during this period an evolutionary milestone occurred that allowed amphibians to move away from humid environments and begin to penetrate even further into terrestrial environments: the amniotic egg appeared.

In this, the embryo is protected by a membrane that prevents its resection, thanks to the fact that it keeps the liquids inside and the exchange with the air. This was a very important fact from the evolutionary point of view, since it allowed the existing groups to colonize more territories on the mainland, having the reproductive process assured.

In the seas, the species that inhabited there continued their process of diversification and proliferation.

Regarding the climate, at the beginning of the period it was hot and humid. However, as time progressed, the temperatures dropped, reaching levels of glaciation.

Permian

It is the last subdivision of the Paleozoic era. It had its beginnings approximately 299 million years ago.

One of the most important events of this period was the formation of the supercontinent Pangea.

The climate became increasingly dry and arid, which favored the development and evolution of some groups of animals such as reptiles. Likewise, within the group of plants, conifers began to proliferate.

Life on the seabed continued to evolve. However, during the Great Dying, almost no species survived, with approximately 95% of marine species becoming extinct.

At the end of the period, environmental conditions underwent a drastic change. The exact causes of this are not known, however it has been established that conditions were no longer favorable for terrestrial and marine species.

This resulted in the famous Permian - Triassic Extinction, which wiped out more than 90% of plant and animal species, both terrestrial and marine.

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