Earth’s protective atmosphere has protected life for billions of years, creating an environment for evolution to produce complex life forms like us. The ozone layer plays an important role in protecting the biosphere from deadly UV rays. Block 99% of the sun’s powerful UV rays. Earth’s magnetosphere also protects us.
But the Sun is relatively interesting. How effectively does the ozone and magnetosphere protect us from powerful supernova explosions?
Every million years – a tiny fraction of Earth’s 4.5 billion years – a giant star explodes within 100 parsecs (326 light years) of Earth. We know this because our solar system exists in a space called the local bubble.
A cavernous space where the density of hydrogen is lower than outside the bubble. During the previous 10-20 million years, an extraordinary explosion carved the bubble.
Supernovae are dangerous, and the closer they are to a planet, the more deadly their effects. Scientists speculate about the impact of the super explosion on Earth, whether it caused a mass extinction, or at least a partial extinction.
Superstar gamma ray bursts and cosmic rays can destroy Earth’s ozone and allow ionizing UV rays to reach the planet’s surface. The effects can also create more aerosol particles in the atmosphere, increase cloud cover, and cause global cooling.
A new Nature Communications Earth and Environment research paper examines supernova explosions and their impact on Earth. It’s called “Earth’s Atmosphere Protects Biosphere from Nearby Supernova”. The lead author is Theodoros Christoudias of the Center for Climate and Atmospheric Research, Cyprus Institute, Nicosia, Cyprus.
The Buber Bubble is not the only evidence of nearby collapsing superstars (SNe) in the past few million years. Ocean sediments contain 60Fe, a radioactive isotope with a half-life of 2.6 million years.
When an SNe explodes, it ejects 60Fe into space, suggesting that a nearby supernova exploded about 2 million years ago. It also contains 60Fe in the sediment which indicates another SN explosion about 8 million years ago.
The graph from this research paper shows the potential effects of nearby stars on their atmosphere and climate. Gamma rays can destroy ozone, allowing more UV radiation to reach the earth’s surface. Some UV radiation is ionizing, meaning it can damage DNA. Cosmic rays can create more clouds and more condensation nuclei, which means global cooling.
Researchers link the SN explosion to the Late Devonian extinction, about 370 million years ago. In one paper, researchers found plant spores burned by UV rays, indicating that something powerful has destroyed the Earth’s ozone layer.
In fact, Earth’s biodiversity has declined for about 300,000 years since the end of the Devonian extinction, suggesting that many SNe may play a role. The Earth’s ozone layer is in constant flux. When UV energy reaches it, it splits the ozone molecule (O3). It dissipates UV energy and oxygen atoms recombine to form O3. the cycle repeats itself.
This is a simplified version of atmospheric chemistry, but it serves to illustrate this cycle. A nearby supernova can deplete the ozone layer, allowing more deadly UV to reach the Earth’s surface.
But in a new paper, Christoudias and co-authors suggest that Earth’s ozone layer is more resilient than previously thought and provides significant protection from SNe within 100 parsecs.
While previous researchers have modeled the Earth’s atmosphere and response to nearby SN, the authors say they have gone one better in this work. To study the effect of nearby SNe explosions on the Earth’s atmosphere, they modeled the Earth’s atmosphere with the Earth System Model and Atmospheric Chemistry (EMAC).
Using EMAC, the authors say they modeled the “complex atmospheric circulation dynamics, chemistry, and processing responses” of Earth’s atmosphere.
This “leads to an increase in ionized nuclei and particles into CCN” (cloud condensation nuclei), necessary to simulate the loss of stratospheric ozone in response to high-level ionization.
Author says “We obtained a representative SN with a GCR (galactic cosmic ray) ionization rate 100 times higher than the current rate in the atmosphere,” they said. This is due to a supernova explosion approximately 100 parsecs or 326 light years away. “Ozone depletion over the poles is less than the current anthropogenic ozone hole over Antarctica, which equates to a loss of 60-70% of the ozone column”.
On the other hand, there is an increase in ozone in the troposphere, but it is only at the level caused by recent anthropogenic pollution.
Reference: Earth’s atmosphere protects the biosphere from nearby supernovae: Nature Communication
Edited By: Edited by Dr. Brijendra Kumar Mishra, (Disaster Risk Reduction Expert)