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Mass extinctions: the five epochal events in Earth's history



The extinction of dinosaurs in the Cretaceous-Paleogene, 65 million years ago, is widely recognized. However, four previous mass extinctions prior to this iconic disappearance have left a profound mark on Earth's history since its formation approximately 4.5 billion years ago. In this essay, we will explore how these extinctions have influenced the course of planetary evolution and analyze their relevance in understanding our current world.


The first mass extinction, known as the Ordovician-Silurian Extinction, occurred approximately 443 million years ago (Prasad, 2022). At that time, Earth was dominated by various species. This extinction was primarily caused by a drastic climate change resulting in global cooling of tropical oceans, a reduction in sea levels, and the loss of habitats in low-lying areas. Additionally, it was related to changes in oxygen concentration in the water, which severely affected marine biodiversity (Harper et al., 2014). Despite the severe consequences of this extinction, life on Earth continued and evolved, setting an example of nature's resilience in the face of catastrophic challenges.


Moving on to the Second Mass Extinction, known as the Devonian Extinction, which occurred approximately 365 million years ago during the Devonian period. It was caused by drastic changes in environmental conditions and atmospheric composition. One of the main factors was the decrease in oxygen in the water, particularly in the oceans. This extinction has been linked to massive volcanic activity, known as the Siberian Traps. These eruptions released large amounts of gases, including sulfur dioxide and carbon dioxide, leading to ocean acidification and global warming. This had a devastating impact on marine and terrestrial biodiversity. Although some species survived and adapted, many others disappeared. This extinction altered the course of evolution, allowing the emergence of new forms of life on Earth.


Now, let's move on to the Third Mass Extinction, known as the Permian-Triassic Extinction, which occurred about 250 million years ago. It is called the "Great Dying" due to the elimination of more than 90% of Earth's species. The primary cause was a drastic climate change caused by the massive release of greenhouse gases, especially a six-fold increase in atmospheric CO2. This was largely due to massive volcanic eruptions, such as the Siberian Traps.


This climate change had devastating effects on life on Earth, leading to the extinction of numerous species, both in the oceans and on land. Despite the catastrophic loss of life, the Permian-Triassic extinction also marked a turning point in the evolution of species, giving rise to new forms of life on Earth.


Continuing, we arrive at the Triassic-Jurassic Extinction, which occurred about 210 million years ago. It was mainly due to massive volcanic eruptions. These eruptions released large amounts of greenhouse gases, leading to a drastic change in climate and the environment. Geological records show evidence of extensive lava flows known as the Central Atlantic Magmatic Province, believed to be responsible for these eruptions. These volcanic events released sulfur dioxide and carbon dioxide, causing significant global warming and ocean acidification. As a result, many species, especially large animals, disappeared, paving the way for the subsequent dominance of dinosaurs on Earth. This extinction illustrates how cataclysmic geological and climatic events can affect Earth's biodiversity.



Extinction Number

Life Span Until Mass Extinction

Dominant Species on Earth

Trigger of Mass Extinction

First

Approximately 443 million years ago

Trilobites and brachiopods

Climate change and glaciations

Second

Approximately 365 million years ago

Armored fish and trilobites

Change in oxygen concentration in water and volcanic activity

Third

Approximately 250 million years ago

Amphibians and reptiles

Climate change due to increase in CO2 and release of greenhouse gases

Forth

Approximately 210 million years ago

Dinosaurs and mammals

Massive volcanic eruptions

Fifth

Approximately 65.5 million years ago

Dinosaurs and mammals

Impact of a 10 km long meteorite

Sixth

It has not happened yet, but its arrival is feared

Humans and diversity of life

Human activity, climate change, loss of biodiversity, among other factors

Finally, we come to the fifth and most recent mass extinction, occurring approximately 65.5 million years ago at the end of the Cretaceous period. It is known as the Cretaceous-Paleogene Extinction (K-Pg) or the Fifth Mass Extinction. It was triggered by the impact of a meteorite approximately 10 km in diameter. This cataclysmic event had a devastating impact on Earth, leading to a series of consequences.


The meteorite impact generated an enormous release of energy, equivalent to the explosion of thousands of nuclear bombs, causing a thermal shockwave that obliterated everything within a radius of approximately 1000 km. This instantaneous heat wave carbonized vegetation and caused massive wildfires worldwide.


In addition to the thermal impact, the meteorite impact also ejected large amounts of dust and particles into the atmosphere, blocking sunlight for weeks or even months. This resulted in a drastic global cooling, known as a "nuclear winter," a phenomenon in which a significant reduction in solar radiation reaching the Earth's surface causes severe and prolonged cooling. This event disrupted photosynthesis processes and severely affected the food chain.


The K-Pg extinction resulted in the complete disappearance of most non-avian dinosaurs, as well as numerous other species. However, it paved the way for the radiation of mammals and, ultimately, for the rise of humans as the dominant species on Earth.


The details of this mass extinction are supported by an extensive fossil record, and evidence of the meteorite impact has been found in the form of craters, such as the Chicxulub crater in Mexico. This mass extinction is a striking example of how cosmic events can have a dramatic effect on the biodiversity of our planet.


Conclusion


Each of the mass extinctions, despite their devastating impact, has demonstrated the astonishing ability of life to recover and evolve. These events mark significant milestones in the history of our planet, and while they led to the rise of new species, such as mammals, they must also serve as reminders of our current responsibility.

Today, we face critical environmental challenges that resemble the conditions before mass extinctions. Human activity is driving climate change, biodiversity loss, and ecosystem degradation. If we do not take urgent and responsible measures, we could become catalysts for a sixth mass extinction. We are at a crucial crossroads in the history of our planet, and our ability to act sustainably and consciously will determine not only our destiny but also that of countless life forms on Earth.


The history of mass extinctions is a striking reminder of the fragility and resilience of life on Earth. We must recognize that these past events hold important lessons for addressing current environmental challenges. If we wish to ensure a sustainable and equitable future for future generations, we must take responsibility for preserving the diversity and beauty of our natural world.

Emliano Teran



References


Ezcurra, M., & Butler, R. (2018). The rise of the ruling reptiles and ecosystem recovery from the Permo-Triassic mass extinction. Proceedings of the Royal Society B: Biological Sciences, 285. https://doi.org/10.1098/rspb.2018.0361.


Prasad, U. (2022). Mass Extinctions in the history of Life: Significance of NASA’s Artemis Moon and Planetary Defence DART Missions. Scientific European. https://doi.org/10.29198/scieu/2208231.


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