Desert lichen may offer clues to life beyond Earth

Can lichen survive on planets blasted with far more solar radiation than Earth? It’s a question that cuts to the heart of whether life could exist beyond our planet. Scientists have been looking to the skies for answers – and now, a new study offers one.

Researchers from the Desert Research Institute (DRI) and the University of Nevada, Reno (UNR) have found that a common lichen growing in the Mojave Desert can survive levels of ultraviolet radiation previously thought to be lethal.

The study shows that this humble desert lichen might hold the key to understanding how life could endure in extreme environments on other worlds.

Why is the lichen black?

The idea for the study started with something small and simple – a color.

“I was just walking in the desert and I noticed that the lichens growing there aren’t green, they’re black,” said Henry Sun, associate research professor of microbiology at DRI.

“They are photosynthetic and contain chlorophyll, so you would think they’d be green. So I wondered, ‘What is the pigment they’re wearing?’ And that pigment turned out to be the world’s best sunscreen.”

That “sunscreen” is a dark pigment on the surface of the lichen, Clavascidium lacinulatum, which lives in harsh, sun-drenched environments like the Mojave. Despite being constantly bombarded with solar radiation, the lichen survives – and thrives.

Exoplanets face UV extremes

Our planet’s atmosphere filters out the most dangerous form of ultraviolet radiation: UVC. It’s the shortest and most harmful of the UV spectrum.

We never experience it on Earth’s surface, but many exoplanets orbit stars that emit it in high doses – especially M and F type stars.

UVC is powerful enough to sterilize hospital rooms. It breaks down DNA and prevents reproduction in even the hardiest microorganisms.

So the idea that anything could live on a planet exposed to that kind of radiation has seemed like a long shot. That is, until now.

90 days under the lamp

Sun and his then-graduate student, Tejinder Singh, collected lichens from the desert near their homes in Las Vegas. They exposed the lichens to nonstop UVC radiation under lab conditions for three months – far longer than most studies of this kind.

“In order for a microorganism to persist on a planet, it has to last longer than a day,” Sun explained. “So, our experiment had to be long enough to be ecologically significant. We also wanted to go beyond just activity and demonstrate viability.”

When the lichen was rehydrated after the experiment, half of the algal cells were still alive. They didn’t just survive – they replicated.

How the lichen survived

To understand the chemical shield protecting the lichen, the team worked with chemists at UNR. Together, they ran experiments that revealed a simple secret: the acids in the lichen’s outer layer function like additives in plastic that prevent UV damage.

The researchers sliced the lichen open and found a dark, protective top layer – like a natural sunblock.

Lichen is a mix of algae or cyanobacteria living in partnership with fungi. When the algal cells were separated from the fungi and protective layer, they couldn’t take the radiation. They died in under a minute.

Sun said what surprised them most was that this protection is not even necessary for survival on Earth. Our atmosphere already blocks UVC. “The protection is a mere bonus thanks to their remarkable UVA and UVB protection,” he said.

Even the air matters

Solar radiation isn’t the only threat. When UV rays interact with certain chemicals in the air – like oxygen and nitric oxide – they can trigger reactions that create reactive oxygen species. These molecules can damage cells even more.

So the team ran another test. They placed the lichen in an oxygen-free environment while continuing UVC exposure. The result: less radiation damage.

“We came to the conclusion that the lichen’s top layer – a less than millimeter thick skin, if you will – assures that all the cells below are protected from radiation,” the researchers wrote.

“This layer acts as a photo stabilizer and even protects the cells from harmful chemical reactions caused by the radiation, including reactive oxygen.”

Life beyond Earth

The takeaway? Planets that seem too hostile might still host life. Microorganisms could adapt, protect themselves, and persist – just like the black lichens in the Mojave Desert.

“This work reveals the extraordinary tenacity of life even under the harshest conditions, a reminder that life, once sparked, strives to endure,” said Singh, who is now at NASA’s Goddard Space Flight Center.

“In exploring these limits, we inch closer to understanding where life might be possible beyond this planet we call home.”

In short, life might not need Earth-like conditions to exist. It may just need a way to adapt – and a very good tan.

The full study was published in the journal Astrobiology.

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