Supernova Explosions Could Lead To Mass Extinctions On Earth - Alternative View

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Supernova Explosions Could Lead To Mass Extinctions On Earth - Alternative View
Supernova Explosions Could Lead To Mass Extinctions On Earth - Alternative View

Video: Supernova Explosions Could Lead To Mass Extinctions On Earth - Alternative View

Video: Supernova Explosions Could Lead To Mass Extinctions On Earth - Alternative View
Video: Earth's mass extinctions | Peter Ward 2023, September

Two and a half and eight million years ago, two supernovae exploded not far from us (by astronomical standards), which could lead to the depletion of the Earth's ozone layer and numerous undesirable consequences for life. A two and a half million year old supernova in particular could have been a serious blow. The Pliocene, the hot and mild era, ended and the Pleistocene, the era of glaciation and ice age, began. Natural variations in Earth's orbit and wobble would probably explain climate change, but a supernova event that happened during this period would have been better suited.

It is believed that the supernova exploded 163-326 light years away (50-100 parsecs). By comparison, our closest stellar neighbor, Proxima Centauri, is 4.2 light years away.

Implications for the Earth

Supernovae can sterilize any inhabited planets in the vicinity if they get in the way of ionizing radiation. Could these supernovae wreak havoc on the existing biology of our planet? Dr. Brian Thomas, an astrophysicist at Washburn University in Kansas, decided to find out for sure and modeled the consequences for biology on the Earth's surface, based on the geological evidence of two supernovae, 2.5 and 8 million years ago, respectively. In his latest work, Thomas studied the propagation of supernova cosmic rays through the atmosphere to the surface in order to understand their effect on living organisms.

Looking at the fossil record during the Pliocene-Pleistocene boundary (2.5 million years ago), we see dramatic changes in fossils and global soil cover. Thomas notes that "there have been changes, especially in Africa, that have shown a shift from more wooded to meadow soil." At the same time, the geological record shows a global increase in the concentration of iron-60, which is a radioactive isotope formed during a supernova explosion.

“We were interested in how exploding stars could affect life on Earth, and it turned out that a few million years ago, life underwent major changes,” says Thomas. "It could be related to a supernova."

For example, at the Pliocene-Pleistocene boundary, there was a change in the number of species. Despite the fact that there were no major mass extinctions, higher rates of extinction were observed in general, the species themselves and vegetation changed.

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Not so deadly

How could a nearby supernova affect life on Earth? Thomas notes with displeasure that supernovae are often exposed in such a light that "the supernova breaks out and everything dies," but this is not entirely true. It's all about the atmosphere. The ozone layer protects biological life from harmful ultraviolet radiation from the sun that alters the genetic background. Thomas compiled models of the global climate, atmospheric chemistry, and radiation transfer (the propagation of radiation in the atmosphere) to better understand how the cosmic ray supernovae could affect the Earth's atmosphere, in particular the ozone layer.

It is worth noting that supernova cosmic rays will not incinerate everything in their path. The intergalactic medium acts as a kind of sieve, slowing down cosmic rays and "radioactive iron rain" (from iron-60) for hundreds of thousands of years. High-energy particles will be the first to arrive on Earth and will interact with our atmosphere differently from low-energy particles that will arrive later. Thomas simulated the depletion of the ozone layer 100, 300 and 1000 years after the first supernova particles began to enter the atmosphere. Curiously, attrition peaked (26%) after 300 years.


High-energy cosmic rays for the 100-year scenario will seep directly through the stratosphere and dump their energy below the ozone layer, depleting it less, while in the 300-year scenario less energetic cosmic rays will contribute more energy into the stratosphere, significantly depleting the ozone layer.

Ozone depletion is a serious threat to surface life.

Mixed effects

Thomas studied several possible devastating effects on biology (erythema, skin cancer, cataracts, slowing of photosynthesis of marine phytoplankton, and damage to plants) at different latitudes as a result of increased UV radiation intensity caused by a decrease in the ozone layer. Increased damage appeared in all directions, increasing with latitude and in line with the changes preserved in the fossil record. However, not all consequences were equally detrimental to organisms. Plankton, the main producer of oxygen, suffered minimal damage. In addition, there was a small increase in the risk of sunburn and skin cancer among humans.


So, could a nearby supernova lead to a mass extinction? It depends on which side you look at, says Thomas: “There is a subtle difference between 'destroying everything and everything' and the suffering of individual organisms. Some plants added to the yield, like soybeans and wheat, while others lost productivity. And it also reflected in the fossil record.

But how supernovae could affect human evolution - this issue Thomas will deal with in his next work.

Ilya Khel