FunNature & AnimalGreat extinctions and climate changes caused by volcanoes

Great extinctions and climate changes caused by volcanoes

In 1982, volcanologists Christopher G. Newhall and Stephen Self devised a logarithmic scale with which they wanted to indicate the violence of an eruption, similar to the Ritcher scale for earthquakes. Thus was born the Volcanic Explosivity Index (IEV), which has values from 0 to 8. Violent eruptions, such as Krakatoa or Tambora, have only reached a value of 7. A British BBC documentary indicated that an IEV value 8 would occur only if the eruption was generated by a supervolcano. Geologists liked the word so much that they have incorporated it into their terminology. A supereruption is the ultimate geological hazard, and we know there were in the past. Let’s make a brief sketch of a few.

To do this, we are going to go a little back in time, a true minutia in geological terms, and a great cataclysm in all the others. The volcano is called Taupo and it is in New Zealand. It is the year 180 of our era. There, and then, there was the most violent eruption known .

The most violent of all from geological parameters. It is not the greatest in terms of magnitude, but it is in intensity. The pyroclastic flows – those fiery clouds that sweep away everything in their path – that exploded in the year 180 carried the inconceivable speed of 800 kilometers per hour . It emitted a volume of materials of 15 cubic kilometers in 15 minutes. That is, 20 million cubic meters per second. It’s hard to imagine something like that.

In total, the eruption expelled between 120 and 150 cubic kilometers of material and represents one of the largest volcanic episodes in the last 5000 years. Of course, the Taupo is a supervolcano, and the IEV of that explosion is at a value of 8, or slightly above. The volcano is under a lake –also called Taupo– because its eruptions were so violent that a stratovolcano could not be formed.

A supervolcano is Earth’s way of committing mass murder . The biggest crisis that animals have suffered is far from the current climate change. Nor was it when the famous meteorite wiped out almost all the dinosaurs, which everyone talks about on social media in a way that is too funny and dilettante – when it was an absolutely horrible catastrophe. And it is necessary to remember that the birds were saved, and they are dinosaurs, as any fan of paleontology knows.

In reality, the greatest crisis for living beings that we generically call animals occurred at the end of the distant Permian .

Let’s go back to that mysterious period, between 298.9 million years and 251.9 million years ago. By then, the emerged lands were united into a single supercontinent called Pangea . This presented an inlet that opened to the east and was surrounded by the great ocean Pantalasa, in which a smaller sea, the Paleo-Tethys, was differentiated, which covered part of what is now southern and central Europe.

Such an extension generated a warm and dry climate, typically continental. In the interior of the tropical and subtropical regions of Pangea vast deserts developed. Likewise, its genesis reduced productive and ecologically diverse coastal areas. Shallow aquatic environments disappeared and many organisms, previously protected on continental shelves, were exposed to increased environmental volatility and seasonal monsoons.

This whole process obviously implied the disappearance of very diverse living beings. But, in general, things were going very well for life. For example, reefs had formed extensive underwater systems that were home to rich biodiversity, just as it is today. The main builders at the time were rough and tabulated corals. Also, in the seas of Pantalasa, strange fish swam, such as the Helicoprion, with spiral teeth lodged in the lower jaw. There were also petalodontiformes – cartilaginous fish with a bulbous body and flattened teeth – and ray-finned bony skeleton fish, such as platysomids.

On the surface of Pangea, life was buzzing just as well. The marshes and swampy environments were populated by ferns, pteridosperms, and lycophytes, a type of vascular plant. In the drier areas of the interior, cycads, ginkos, gnetophytes and protoangiosperms – the precursors of flowering plants – were abundant. As for the terrestrial vertebrates, the Permian is spiced by a rich amalgam of very striking reptiles , as if they came from an alien world.

Let us now travel to the last stages of that period, to see what happened. At the end of the Guadalupian era – between 272.3 million years ago and 259.8 million years ago – a crisis takes place: the extinction of the end of the Capitanian .

It is believed to have been caused by one or more eruptions of the Emeishan traps – huge stacks of volcanic basalt rock flows, the edges of which have a stepped profile – that released a large amount of carbon dioxide and sulfur dioxide into the stratosphere. , as a consequence of intense volcanic activity and associated climatic changes. This is the first indication that the Earth’s mantle was in a phase that would eventually release huge amounts of magma.

After the Guadalupian came the Lopingian, the last geological period of the Permian. It began 259.1 million years ago and lasted for about 7 million years. The last geological floor of the Lopingian is called Changhsingian – between 254.14 million years ago and 251.9 million years ago. The Changiense houses the last 2 years of the Permian. It is in this interval when the worst extinction of animal life takes place.

Surprisingly, Pangea vertebrates had the same diversity in the early Changhsingian as they did in the early Permian, with 39 families found throughout the world. Gone were the bad times of the Captain. In the seas there were paleonisciform fish, amphibians and chronosuquids – similar in appearance to crocodiles.

Among the terrestrial vertebrates there were abundant herbivores, such as the Scutosaurus, small lizards, such as the Paliguana, the dicinodonts – robust reptiles protected with different types of osteoderms -, such as the Dicynodon, and the carnivorous gorgonopic reptiles, such as the Inostrancevia, which were the main predators of that time. Everything indicates that tetrapods had reached high levels of complexity, possibly as much as modern mammalian communities.

Right at the end of the Changhsingian is when a true volcanic apocalypse occurs, in what is now Siberia. No current geological phenomenon remotely resembles what happened. And it was a consequence of the arrival of a mantle feather, the largest of the envelopes that make up the planet.

The mantle sits between the silica-rich crust in which we live and the dense, iron-rich core. A combination of heat and gravity causes it to flow and undergo large-scale convection motions. The flow produces regions of the mantle that are at higher temperatures than their surroundings and from which very hot but still solid rocks rise, forming what is called a plume.

The rising plumes are believed to originate in the lower part of the mantle – a level geophysicists call D ”, from the heat emitted by the Earth’s core. They have large heads and thin tails, a bit like mushrooms. The head, meanwhile, continues to grow as the plume ascends towards the earth’s crust.

When it has reached the top of the mantle, on a journey that has taken about 20 million years, the head of the feather flattens – like an open mushroom -, reaching a diameter of up to 2,500 kilometers, with a stem – the tail – between 100 and 200 kilometers wide.

252 million years ago, the bulk of the plume reached the uppermost part of the mantle to trigger massive eruptions , spewing vast amounts of lavas and formidable clouds of ash and gases over 500,000 years. In present-day Siberia, a gigantic expanse of fissured terrain was formed from which sources of lava emanated from countless places kilometers high and formed fiery seas. Today there are only large basalt plateaus called traps, witnesses of that thermal plume. The region is covered by millions of square kilometers of basalt rock, with a volume of about 4 million cubic kilometers of emitted materials.

It is estimated that the Siberian traps may have pumped up to 40,000 gigatons of carbon dioxide into the atmosphere , up to 1,000 times the amount that already existed. Much of the carbon dioxide came directly from the boiling magma, but it is believed that there were additional carbon emissions from the combustion of carbon deposited in the Earth’s crust.

This amount of carbon dioxide released would cause a strong greenhouse effect and consequent warming, with many side effects. A biologically important consequence is that as the oceans warm, their oxygen-holding capacity decreases . This alone could suffocate many organisms that live in already poorly oxygenated areas of the sea. But it is that, in addition, they suffered carbon dioxide poisoning and heat stress.

Bacteria capable of metabolizing sulfates in seawater – purple bacteria – thrived in low oxygen conditions and generated more carbon dioxide, as well as hydrogen sulfide, which was released from surface waters and into the atmosphere. The presence of large amounts of hydrogen sulfide is bad news for almost all animals, plants and fungi because it inhibits the functioning of the mitochondria, which are vital for metabolic processes.

The sea ended up being a feast of purple bacteria that turned the water pink and infused it with the smell of rotten eggs. A large release of hydrogen sulfide would also have a profound impact on the oxidation state of the atmosphere which, through various chemical reactions, would end up increasing the abundance in the air of methane – a greenhouse gas – while depleting the stratosphere of its ozone, which filters biologically harmful ultraviolet radiation.

Animal life was close to complete annihilation. However, a lucky 5 percent of the species survived and managed to diversify after the episode. It was a very fortunate event for mammals that, in the early Triassic , began to flourish, with so many ecological niches available. From those primitive mammals we all descend today.

It can be said that if it was not for the event in Siberia we would not be here, but the scares did not end . Later there was the impact of an extraterrestrial bolide at the end of the Cretaceous – 66 million years ago – which caused another mass extinction. Mammals held out and primates began to diversify during the Tertiary. There was less left for humanity to enter the scene. However, another volcanic event directly affected our species.

Toba is a caldera located in the extreme north of the island of Sumatra (Indonesia). When it erupted some 74,000 years ago, it expelled more than 3,200 cubic kilometers of material.

The ashes of the explosion reached Lake Malawi, in East Africa, and the archaeological site of Pinnacle Point (South Africa), reaching an area of more than 21 million square kilometers. In the middle of the Indian Ocean, the ash layer is 34 centimeters thick. The Toba volcano has had other eruptions, but the one from 74,000 years ago is such an important geological event that it is known as Youngest Toba Tuff – Toba’s youngest volcanic ash. All geologists abbreviate it as YTT.

The supervolcanic eruption had dramatic consequences as far away as inland India. Volcanologists have studied the events that took place in the Jurreru River Valley. What had previously been a lush habitat became, practically suddenly, a devastated land without vegetation, due to the gigantic eruptive clouds that reached the region.

The umbrella cloud that formed had a high concentration of sulfur aerosols, which gave it a white color. White reflects light very well. The ashes scattered over the earth’s surface, also whitish in color, had the same effect, similar to that of snow. The result was a drop in global temperature of between 3 and 5 degrees Celsius .

The Earth’s climate still became much drier and colder. And it must be borne in mind that by then an ice age was already taking place. The Toba episode chilled a planet already covered with snow in many areas a little more. The catastrophe had human witnesses.

A team of archaeologists led by Michael Petraglia, from the University of Oxford, found lithic tools at a site in the Jurreru Valley called Jwalapuram, in Andhra Pradesh, in southern India. The tools appear below the YTT and, in Petraglia’s opinion, were made by Homo sapiens. Apparently there were modern humans living in the area before the eruption. But, after the cataclysm, what happened? Molecular biologists have found that all humans today are more genetically similar to each other than the chimpanzee populations of West Africa.

Laboratory studies on the entire diversity of ‘Homo sapiens’ show that our species went through a very narrow genetic bottleneck not long ago . The most recent evidence puts the total bottleneck population at 30,000, although most hypotheses are between 4,500 and 5,000.

Some trials suggest that the drastic reduction took place around 70,000 years ago. Of course, YTT has been linked to that genetic bottleneck in human evolution.

The effects of the global climate were able to decimate the size of the populations of many animals, including humans. The hypothesis has been supported by renowned geologists, such as Michael R. Rampino of New York University, and volcanologist Stephen Self, as well as archaeologist and paleoanthropologist Stanley H. Ambrose, of the University of Illinois at Urbana-Champaign, who has worked in various deposits in the Jurreru valley.

Thus, it seems that our species was about to disappear from the face of the planet 74,000 years ago because of a volcano . The “mother” Earth maintains a constant pulse with life. Agencies have repeatedly gone through these bottlenecks due to major climate catastrophes, but to date they have emerged victorious. Life is tenacious, and that quality is a moral loaded with positive meaning.

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