کد خبر: 215568تاریخ: 1397/3/2 06:16
Supernovas which took place millions of years ago have caused extinction on Earth
Supernovas which took place millions of years ago have caused extinction on Earth
Two supernovae which exploded between 2½ and eight million years ago could have caused mass extinction because it affected the Earth’s ozone layer, according to major new scientific discoveries.

The supernova is thought to have occurred between 163 and 326 light-years away (50–100 parsecs) from Earth, wrote.

Harmful ionizing radiation can sterilize nearby inhabited planets and one researcher wanted to discover if it was the cause for mass extinction on Earth based on geologic evidence of nearby supernovae.

Astrophysicist at Washburn University in Kansas Brian Thomas investigated cosmic rays from the supernovae as they propagated through the atmosphere to the surface to understand their effect on living organisms.

Speaking to Astrobiology Magazine, Thomas said, “There were changes, especially in Africa, which went from being more forested to more grassland.

"We are interested in how exploding stars affect life on Earth, and it turns out a few million years ago there were changes in the things that were living at the time.

"It might have been connected to this supernova."

During the time period, geologic records show an elevated global concentration of Iron-60 which is a radioactive isotope produced during a supernova.

There was a change in the abundance of species during the Pliocene-Pleistocene period.

No major mass extinctions happened but there was a higher rate of extinction in general.

Thomas added Earth’s ozone layer protects all biology from harmful, genetically altering ultraviolet (UV) radiation.

He used global climate models, recent atmospheric chemistry models and radiative transfer (the propagation of radiation through the layers of the atmosphere) to investigate and better understand how the flux of cosmic rays from supernovae would alter Earth’s ozone layer.

Thomas said that supernovae does not blast everything at once.

Instead the intergalactic medium acts as a kind of sieve, slows down the arrival of cosmic rays and ‘radioactive iron rain’ over hundreds of thousands of years.

A decrease in ozone could be a concern for life on the surface.

When asked if nearby supernovae will result in mass extinctions, Thomas said it depends.

He added, "There is a subtler shift; instead of a 'wipe-out everything’, some organisms are better off and some are worse off.”

For example plants showed increase yield, like soybean and wheat, while others showed reduced productivity.

Referring to the changes in species in the fossil record, Thomas said that it fits.

Computational physicist at the Blue Marble Space Institute of Science in Seattle Dimitra Atri said, "This work is an important step towards understanding the impact of nearby supernovae on our biosphere.”


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