Earth’s protective atmosphere has protected life for billions of years, creating a haven where evolution could produce complex life forms like us.
The ozone layer plays a vital role in protecting the biosphere from deadly ultraviolet radiation. It blocks 99% of the sun’s powerful ultraviolet radiation. Earth’s magnetosphere also protects us.
But the Sun is relatively docile. How effective would the ozone layer and magnetosphere be in protecting us from a powerful supernova explosion?
Every million years, a tiny fraction of Earth’s 4.5 billion year lifespan, a massive star within 100 parsecs (326 light years) of Earth explodes. This is well known because our solar system sits in a giant bubble of space. Local Bubble.
It’s a cavernous region of space where the density of hydrogen is much lower than outside the bubble. The bubble was formed by a series of supernova explosions over the past 10 to 20 million years.
Supernovae are dangerous, and the closer a planet is to a supernova, the more deadly its effects will be. Scientists have speculated about the effects of a supernova explosion on Earth, wondering if it could have caused a mass extinction, or at least a partial extinction.
Gamma-ray bursts from supernovae and cosmic rays can destroy the Earth’s ozone layer and cause ionizing ultraviolet radiation to reach the Earth’s surface, which can increase aerosol particles in the atmosphere, increase cloud cover, and cause global cooling.
New research paper Nature Communications Earth and the Environment We will investigate supernova explosions and their effects on Earth. The title is “Earth’s atmosphere protects the biosphere from nearby supernovae.“
Lead author is Theodoros Christoudias from the Cyprus Institute Centre for Climate and Atmospheric Research in Nicosia, Republic of Cyprus.
The Local Bubble is not the only evidence of nearby supernova explosions (SNe) that have occurred in the past few million years. Marine sediments also contain 60Fe is a radioactive isotope of iron with a half-life of 2.6 million years.
SNe Expulsion 60The explosion spewed Fe into space, indicating that a nearby supernova exploded 2 million years ago. 60Fe in the sediments indicates that there was another SN explosion about 8 million years ago.
Researchers say that SN explosions Late Devonian extinction About 370 million years ago. In one paperResearchers have found plant spores burned by ultraviolet light, a sign that something powerful is destroying Earth’s ozone layer.
Indeed, Earth’s biodiversity declined for about 300,000 years before the Late Devonian extinction, suggesting that multiple supernovae may have played a role.
Earth’s ozone layer is constantly changing. When ultraviolet energy reaches the ozone layer, it breaks down ozone molecules (O3), which dissipates the ultraviolet energy and causes oxygen atoms to recombine into O3. The cycle repeats.
It’s a simplified version of atmospheric chemistry, but it helps explain the cycle: a nearby supernova explosion could overwhelm the cycle, reducing the density of the ozone layer and allowing more deadly ultraviolet radiation to reach Earth’s surface.
But in a new paper, Christoudias and his co-authors suggest that Earth’s ozone layer is much stronger than previously thought, and could provide plenty of protection against a supernova within 100 parsecs of our time.
Previous researchers have modeled Earth’s atmosphere and how it might respond to a nearby supernova, but the authors say they have improved on that work.
They modelled Earth’s atmosphere with the Earth System Model with Atmospheric Chemistry (EMAC) to study the effects of a nearby supernova explosion on Earth’s atmosphere.
The authors say they used EMAC to model the “complex atmospheric circulation dynamics, chemistry and process feedbacks” of Earth’s atmosphere.
These are necessary to simulate “the loss of stratospheric ozone in response to increased ionization, leading to ion-induced nucleation and particle growth into CCNs (cloud condensation nuclei).”
“We envision a representative nearby supernova with an atmospheric GCR (galactic cosmic ray) ionization rate 100 times higher than the current rate,” the researchers wrote, which correlates with a supernova explosion occurring about 100 parsecs, or 326 light-years, away.
“The maximum depletion of the ozone layer over the poles is less than the anthropogenic ozone hole currently occurring over Antarctica, which corresponds to a 60-70% loss of ozone columns,” the authors explain.
“Meanwhile, tropospheric ozone is increasing, but it is within the levels caused by recent anthropogenic pollution.”
But let’s get to the point: we want to know if the Earth’s biosphere is safe.
The maximum average depletion of the stratospheric ozone layer from 100 times the normal amount of ionizing radiation, typical of a nearby supernova, would be about 10% globally, roughly the same as the depletion caused by human pollution, and would not have a significant effect on the biosphere.
“Although changes to the ozone layer are significant, they are unlikely to have major impacts on the biosphere, especially since most of the ozone loss is occurring at high latitudes,” the authors explain.
But that’s the case on modern Earth: in the Precambrian era, before life exploded and diversified, there was only about 2% oxygen in the atmosphere. How do SNs affect this?
“We simulated an atmosphere with 2% oxygen because this is likely to reproduce conditions under which a new terrestrial biosphere would be particularly sensitive to ozone depletion,” the authors write.
“Ozone losses are about 10-25% at mid-latitudes and an order of magnitude lower in the tropics,” the authors write. At the lowest polar ozone levels, ionizing radiation from SNs could actually lead to ozone gains.
“We conclude that these changes in the atmospheric ozone layer are unlikely to have had a significant impact on the terrestrial biosphere that emerged during the Cambrian,” the researchers conclude.
What about global cooling?
The planet would cool, but not to dangerous levels. In the Pacific and Antarctic oceans, CCN could increase by up to 100 percent, which seems like a pretty big increase. “These changes, which are relevant to climate, would be comparable to the contrast between the clean air of pre-industrial times and the polluted air of today.”
They say it would cool the atmosphere by roughly the same amount as we are currently warming it.
The researchers point out that their study pertains to the entire biosphere, not to individuals: “Our study does not consider the direct health risks to humans or animals from exposure to high concentrations of ionizing radiation,” they write.
Individual circumstances could expose people to dangerous levels of radiation over time, but overall, the biosphere would function just fine even with a 100-fold increase in UV radiation; the atmosphere and magnetosphere could withstand it.
“Overall, we find that a nearby supernova is unlikely to have caused a mass extinction on Earth,” the authors write.
“We conclude that Earth’s atmosphere and geomagnetic field effectively protected the biosphere from the effects of a nearby supernova, allowing life to evolve on land over the past hundreds of millions of years.”
The study shows that unless a supernova explosion occurs, Earth’s biosphere will not suffer significant damage.
This article is The Universe Today. read Original Article.
