An Astrophysicist has recently found that two nearby supernovas that exploded 2.5 and 8 million years ago could have produced a phased depletion of the ozone layer and consequently an adjustment in the life of the Earth.
Precisely then, 2.5 million years ago, Earth was going through a turbulent time as the surface changed dramatically. Our planet was switching from the Pliocene to the Pleistocene— colloquially referred to as the Ice Age.
The Pleistocene is marked by repeated glacial cycles in which continental glaciers pushed to the 40th parallel in some places.
One of the questions we need to be asking is whether the nearby supernovae could have wreaked havoc on the existing biology of our planet.
To answer this question, Brian Thomas, an astrophysicist at Washburn University in Kansas, modeled the biological impacts on the surface of the Earth, based on the geological evidence of nearby supernovae 2.5 million and 8 million years ago.
In his latest article, Thomas investigated the cosmic rays of the supernovas as they propagated through our atmosphere to the surface, to better understand their effect on living organisms on Earth.
Studying Fossil Records
Looking at a number of Fossil records of the Pliocene–Pleistocene boundary, we notice a general, dramatic change in the fossil record and land cover.
Speaking to Astrobiology Magazine, Thomas explains “there were changes, especially in Africa, which went from being more forested to more grassland.”
Curiously, the geological record of that time shows an elevated concentration of iron–60 (60Fe), which is a radioactive isotope produced during a supernova.
“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,” says Thomas. “It might have been connected to this supernova.”
The Earth Recorded a number of Changes
The researcher found that changes did occur, and they weren’t that deadly, although they did affect the Earth and life on the planet.
Thomas explained there was a change in the abundance of species during the Pliocene-Pleistocene boundary. Although there were no large mass extinctions, there was a higher rate of extinction in general, more speciation and a change in vegetation.
How a Supernova can change things on Earth
Beyond protecting our planet from the Sun, the ozone layer of our planet protects the entire biology from the harmful ultraviolet (UV) radiation that can alter biology on a genetic level.
Using a number of climate models, like recent atmospheric chemistry models, and radiative transfer (the spread of radiation through the layers of the atmosphere) Thomas tried to understand better how the supernova’s cosmic ray flux would modify Earth’s atmosphere, particularly the ozone layer.
“One thing to note is that cosmic rays from supernovae would not blast everything in their paths all at once. The intergalactic medium acts as a kind of sieve, slowing down the arrival of cosmic rays and “radioactive iron rain” (60Fe) over hundreds of thousands of years, Thomas told the Astrobiology Magazine.
The astrophysicist examined several possible biologically damaging effects like erythema, skin cancer, cataracts, inhibition of photosynthesis of marine phytoplankton and damage to plants at different latitudes as a result of the increase in UV radiation resulting from an impoverished ozone layer.
They showed more significant damage in general, increasing with latitude, which makes sense given the changes we see in the fossil record.
However, the effects are not equally harmful to all organisms.
Thomas explains that plankton, which are the primary producers of oxygen, seemed to be minimally affected by the cosmic event.
The results also seemed to indicate a small increase in the risk of sunburn and skin cancer among humans.
So, the million-dollar question is: do nearby supernovae result in mass extinctions?
It depends, says Thomas. “There is a subtler shift; instead of a ‘wipe-out everything,’ some [organisms] are better off, and some are worse off.” For example, some plants showed increase yield, like soybean and wheat, while other plants showed reduced productivity.
“It fits,” Thomas states, referring to the change in species in the fossil record.