Are supernovae responsible for mass extinctions?

Are supernovae responsible for mass extinctions?

UV radiation from a nearby supernova can lead to changes in life on Earth

The two nearest supernovae, which exploded about 2.5 and 8 million years ago, could have led to a dramatic depletion of the ozone layer of the Earth, which caused many consequences for life.

In particular, 2.5 million years ago, the Earth has changed dramatically. The Pliocene (hot and mild epoch) ended and the Pleistocene began (ice age). Natural variations in terrestrial orbit and fluctuations probably explained climate change, but a supernova event could provide insight into the diversification of life in that era.

It is believed that the supernova exploded at a distance of 163-326 light years from Earth. To understand the scale, the nearest star Proxima Centauri is distant by 4.2 light years.

Consequences for the Earth

Supernovae are capable of sterilizing any nearby populated objects located along the pathway of their harmful ionizing radiation. Can nearby supernovae harm terrestrial biology? To understand this, scientists from the University of Kansas modeled biological effects on the earth's surface, based on evidence from nearby supernovae 2500 and 8 million years ago. Looking at the fossils with an age of 2.5 million years ago, one can notice a dramatic change, as in the land cover. This is especially clearly seen in Africa, where the woodland has been replaced by meadows and pastures. At that time, the records show an increased global concentration of iron-60 - a radioactive isotope that is formed during the supernova period.

Are supernovae responsible for mass extinctions?

Globally averaged change in ozone density as a percentage difference of 100, 300 and 1000 years after a nearby supernova explosion

Analysis has shown that explosions affect biology. For example, there was a change in the number of species on the border of the epochs under consideration. Major mass extinctions were not recorded, but higher rates of extinction were observed as a whole.

Not quite deadly

How does a supernova affect Earth? The answer lies in the atmosphere. The ozone layer saves all biology from harmful, genetically changing UV radiation. When using global climate models, recent analyzes of atmospheric chemistry and radiation transfer have shown how the flow of cosmic rays from supernovae will change the earth's atmosphere, namely the ozone layer.

It is important to note that the cosmic rays from supernovae will not demolish everything in their path. The intergalactic medium works as a sieve, slowing its progress for hundreds of thousands of years. Higher energy particles will get to our atmosphere and will be in contact with the atmosphere. The model showed ozone depletion in the intervals of 100, 300 and 1000 years after the initial particles penetrated into the atmospheric layer. Interestingly, the peak of exhaustion (26%) fell on the 300-year-old.

Are supernovae responsible for mass extinctions?

One of the last supernovae that exploded in the Milky Way. This is the remainder of the supernova Cassiopaea, which exploded more than 300 years ago at a distance of 11,000 light years.

Mixed Effects

Reducing ozone levels can be a problem for earthly life. Scientists have studied several possible biologically damaging effects (skin cancer, cataracts, inhibition of photosynthesis, damage to plants) at different latitudes due to an increase in UV rays. The analysis showed increased damage in all directions, increasing with latitude. But effects are not equally harmful to all organisms. For example, minimal changes have touched plankton. The findings also indicate an increased risk of sunburn and skin cancer among people. Therefore, supernovae do not cause mass extinctions, but act on a more subtle plane, activating the chain of changes.

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