According to a recent study, the reason for oneof the most mass extinctions, which occurred 350 million years ago, was the reduction of oxygen in the oceans and the increase in the amount of hydrogen sulfide. According to scientists, these changes were due to rising sea levels. It must be said that this is not the only extinction on Earth associated with hydrogen sulfide, but scientists have never been engaged in a thorough study of such extinctions before. Now, researchers have not only carefully examined this process, but also drew parallels with the current situation. As it turned out, extinction may well repeat in our days.
Devonian mass extinction
In their study, the researchers focusedfocus on black shales mined in the Bakken Formation. This region has an area of more than half a million square kilometers. It is located partly in North Dakota and Canada. In the course of their work, the authors found traces of the fact that our planet once experienced periods of oxygen deficiency, which primarily affected the oceans.
According to the researchers, this led tolarge-scale extinction that occurred in the Devonian period, which lasted from 419.2 to 358.9 million years ago. Note that such extinctions did not occur all at once, as in the case of extinction as a result of an asteroid impact 66 million years ago, when all non-avian dinosaurs died. Extinctions due to natural causes could last for thousands of years, as happened 250 million years ago, as we talked about earlier.
The Devonian period is also called the "epochfish”, since at that moment marine life was actively developing. Jawless fish, or placoderms, inhabited the oceans along with ancient arthropods called trilobites, as well as ammonite cephalopods.
During this period, forests began to cover the land,consisting of ferns and the first trees. It was during this period that the fish began to come ashore. As a result, the four-legged creature taktaaliki arose. We talked about the evolution of fish and the first land creatures of this period of time.
However, as a result of extinction, many creaturesDevonian period subsequently disappeared from the face of the Earth. These include placoderms, trilobites, and early ammonites. At the same time, some fish such as cartilaginous sharks and rays bred.
How the Mass Extinction Happened 350 Million Years Ago
To understand what happened in the Devonian period,scientists and researchers of more than 100 core samples, mined, as we said above, in the Bakken formation. The black shales here accumulated mainly in the late Devonian, resulting in a good reflection of the chemical composition and environment of this time period, as the researchers report in the journal Nature.
The study showed that the reason for the lossoxygen was a sharp rise in water levels due to the melting of ice caps at the Earth's poles. Melting actively lasted from 443.8 to 419 million years ago. Scientists believe that minerals, which began to be washed out of the rocks and enter the water in large quantities, caused the reproduction of algae and their abundant flowering. Then the plants died and decomposed, as a result of which hydrogen sulfide was released in large quantities and oxygen was absorbed. This led to the fact that 75% of all life on Earth died out.
Mass extinction could happen again?
According to some scholars, we alreadywe are on the verge of the sixth mass extinction (rather the seventh, since the sixth extinction in the history of the Earth has already happened) or even entered it. It occurs not only on land, but also in the oceans, where so-called “dead zones” appear annually, that is, areas where the oxygen content is at a critically low level.
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As the reason for this phenomenon, scientists callnot even global warming, although it also contributes, but the intensive use of fertilizers in agriculture. Fertilizers are washed away with water and end up in the ocean, where they cause algae blooms. Of course, the causes are different from those that arose 350 million years ago, however, according to scientists, the results may be the same. Thus, the events of the past tell scientists about the threats of the present.