Earth’s protective atmosphere protected life for billions of years and provided a haven where evolution created complex life forms like us. The ozone layer plays a crucial role in protecting the biosphere from deadly UV radiation. It blocks 99% of the Sun’s strong ultraviolet radiation. The Earth’s magnetosphere also contains us.

However, the Sun is relatively docile. How effectively do ozone and the magnetosphere protect us from powerful supernova explosions?

Every million years, a fraction of Earth’s 4.5 billion years, a massive star explodes within 100 parsecs (326 light-years) of Earth. We know this because our solar system is located in a huge bubble in space called a local bubble.

This is a cavernous region of space where the hydrogen density is much lower than outside the bubble. A series of supernova explosions over the previous 10-20 million years formed this bubble. Supernovae are dangerous, and the closer the planet is to them, the more deadly the consequences. Scientists speculate about the effects of supernova explosions on Earth, wondering whether they trigger mass extinctions or at least partial extinctions.

Supernova gamma-ray bursts and cosmic rays can destroy Earth’s ozone and allow ionizing ultraviolet radiation to reach the planet’s surface. This effect can also create more aerosol particles in the atmosphere, increasing cloud cover and causing global cooling.

A new research article in the journal Nature Communication Earth and Environment He studies supernova explosions and their effects on Earth. It’s called “Earth’s Atmosphere Protects the Biosphere from Nearby Supernovae.” The lead author is Theodoros Christudias from the Cyprus Institute Center for Climate and Atmospheric Research in Nicosia, Cyprus.

The Local Bubble is not the only evidence of nearby supernovae (SNe) over the last few million years. Ocean sediments also include: ⁶⁰ Fe is a radioactive isotope of iron with a half-life of 2.6 million years.

SNe removed ⁶⁰ The fact that Fe was expelled into space when it exploded indicates that a supernova exploded nearby about 2 million years ago. There are also deposits ⁶⁰ Fe indicates another SN explosion about 8 million years ago.

Researchers linked the SN explosion to the Late Devonian extinction about 370 million years ago. In one paper, researchers found plant spores burned by UV rays; This suggests that something powerful is depleting Earth’s ozone layer.

In fact, Earth’s biodiversity declined approximately 300,000 years before the Late Devonian extinction; this suggests that multiple SNes may have played a role. The Earth’s ozone layer is constantly changing. When UV energy reaches it, it breaks down ozone (O3) molecules. This dissipates the UV energy and the oxygen atoms recombine to form O3. The cycle repeats itself.

This is a simplified version of atmospheric chemistry, but it serves to explain the cycle. The next supernova could break the cycle, reducing the density of the ozone layer and allowing more deadly UV to reach the Earth’s surface. But in a new paper, Christoudias and his co-authors suggest that Earth’s ozone layer is much more stable than previously thought, providing sufficient protection against SNe within 100 parsecs.

While previous researchers have modeled Earth’s atmosphere and its response to nearby SNs, the authors say they have improved upon this work. They modeled Earth’s atmosphere using the Earth Systems Model with Atmospheric Chemistry (EMAC) to study the effects of nearby SNe explosions on Earth’s atmosphere.

The authors say they modeled the “complex atmospheric circulation dynamics, chemistry, and feedback processes” of the Earth’s atmosphere using EMAC. “These are needed to simulate stratospheric ozone loss in response to increased ionization, leading to ion-induced nucleation and growth of particles into CCN (cloud condensation nuclei).

“We hypothesize a representative range of atmospheric GCR (galactic cosmic ray) ionization rates near the SN that are 100 times the current rate,” they write. This corresponds to a supernova explosion approximately 100 parsecs, or 326 light-years away.

“The maximum depletion of the ozone layer over the poles is less than the current anthropogenic ozone hole over Antarctica, which represents a loss of 60–70% of the ozone column,” the authors explain.

“On the other hand, there is an increase in ozone in the troposphere, but this is within the range of levels obtained as a result of recent anthropogenic pollution.”

But let’s get back to business. We want to know whether Earth’s biosphere is safe.

The maximum average depletion of the stratospheric ozone layer due to ionizing radiation, which is 100 times the normal representative of the nearest SN, is about 10% worldwide. This amounts to almost the same reduction as our anthropogenic pollution. It will not significantly affect the biosphere.

“Although important, such ozone changes are unlikely to have a major impact on the biosphere, especially since most ozone loss occurs at high latitudes,” the authors explain.

But this is true for the modern World. During the Precambrian period, before life evolved into proliferating forms, there was only around 2% oxygen in the atmosphere. How will SN affect this?

“We modeled an atmosphere containing 2% oxygen because this likely represents conditions under which the terrestrial biosphere would be particularly sensitive to ozone depletion,” the authors write.

“Ozone loss is approximately 10-25% in mid-latitudes and even lower in the tropics,” the authors write. At minimum ozone levels at the poles, ionizing radiation from the SN can cause an increase in the ozone column.

“We conclude that these changes in atmospheric ozone are unlikely to have had a major impact on the formation of the biosphere on land during the Cambrian.”

What about global cooling?

Global cooling will increase, but not to a dangerous degree. In the Pacific and Southern Oceans, CCN can reach 100%, which seems like a lot. “Despite their climatic significance, these changes are comparable to the contrast between the pristine pre-industrial atmosphere and the polluted modern atmosphere.”

They say this will cool the atmosphere as much as we are warming it now.

Researchers state that their study concerns the entire biosphere, not individual humans. “Our study does not take into account the direct risks to human and animal health from increased exposure to ionizing radiation,” they write.

Depending on individual circumstances, people may be exposed to dangerous levels of radiation over time. But overall the biosphere will hum despite a 100-fold increase in UV radiation. Our atmosphere and magnetosphere can handle this.

“Overall, we find that nearby SNe is unlikely to cause mass extinctions on Earth,” the authors write.

“We conclude that our planet’s atmosphere and geomagnetic field effectively protected the biosphere from the effects of nearby SNe, allowing life to flourish on land over the last hundreds of millions of years.”

This study shows that Earth’s biosphere will not be affected as long as supernova explosions are kept at bay.