How rare is life in the universe?
Grad student hopes to answer one of our most intriguing mysteries
Doctoral candidate Andrew Gangidine and UC geology professor Andrew Czaja are working together to unravel this fundamental question.
Gangidine is studying microbial life in silica hot springs to come up with a useful indicator of life on Mars. For the past two years, he has conducted fieldwork in the geyser basins of Wyoming’s Yellowstone National Park to examine what elements are associated with bacteria that live in these geothermal pools.
Meanwhile, Czaja, an assistant professor in UC's McMicken College of Arts and Sciences, serves on a NASA advisory committee that will decide where on Mars to send the next remote-controlled rover. Among other objectives, the rover will look for evidence that life once existed on the red planet.
“We want to remain objective. Some people think there has to be life on Mars,” Gangidine said. “Others think there certainly isn’t life on Mars. And either side has a good chance of being correct.”
Although life cannot exist on the surface of Mars today—solar radiation split surface water into its elemental parts nearly 3 billion years ago—scientists are debating whether life might exist somewhere deep underground, among pockets of water trapped around geothermal areas similar to Yellowstone’s geysers.
And as to whether Mars ever sustained life above ground, scientists are prepared to look for fossil evidence of bacterial life dating back 3 billion years. Gangidine said the good news is that similar fossils of early bacterial life have been found on Earth. This makes him optimistic that if similar life ever existed on Mars, NASA has a chance of finding a fossil record of it.
“We can look at life being preserved in these silica deposits today. We have evidence of this happening throughout geologic time,” Gangidine said. “What we’re trying to do is catch fossilization as it happens. What happens to the microbes themselves? And what happens to the trace elements associated with them while they’re alive?”
Dangerous work on Earth
To unearth clues about ancient life on Mars, Gangidine and his team look to hot springs such as those found in America’s first national park. But exploring the geyser basins can be tricky and dangerous. A tourist died in 2017 after falling into one of the basin’s boiling pools while hiking off-trail.
“These things really can strip the flesh off your bones,” Gangidine said. “At the bottom of hot springs we study you see skulls of bison and other animals that were unfortunate enough to wander too close.”
Sometimes, they can see where a bison’s hoof has broken through the thin crust to reveal steaming mud.
Boiling acid and lava-like mud aren’t the only hazards for researchers in the geyser basins. They also have to be careful not to spend too long around the steam vents, which contain a mix of gases such as carbon dioxide, hydrogen sulfide and methane that can asphyxiate a person under the right conditions.
But even in the fresh air, the gas rising from the ground can have a cumulative effect.
“These hot springs emit a lot of gases you don’t want to breathe in. They bind to the hemoglobin that carries oxygen through your body. Breathing that in, you get very fatigued,” Gangidine said.
Ancient bacteria leads the way
“Hot springs make silica deposits that preserve life really well,” Gangidine said. “When left exposed on a planet’s surface, it doesn’t crystallize and doesn’t metamorphose. So these samples should be relatively well preserved if we find them.”
Looking at chunks of Yellowstone silica taken from a mountainous steam cone geyser, Gangidine notes that the samples taken at the top of the geyser are full of color. But the older samples, some perhaps thousands of years old, are colorless, even if they hold their shape. To uncover more clues about this basic form of life, Gangidine subjects the bacterial samples to elemental analysis using a secondary ion mass spectrometer. The analysis renders the elements in vivid color: deep yellows, reds and greens representing chromium or gallium perhaps associated with the bacterial life.
If Gangidine finds a correlation between the concentrations and spatial distributions of particular elements and the bacteria, it might serve as a biosignature that scientists can use to identify past life on Mars.
“We chose gallium because it’s not known to be associated with life. But when we look at the fossilized bacterial samples, we find it, so there must be something going on,” Gangidine said. “Do the bacteria store certain elements preferentially as opposed to what you would find elsewhere in these rocks?”
“If I want to create a biosignature, I have to prove that it persists throughout time,” Gangidine said. “It exists in these relatively younger samples. But does it exist in these ancient samples, too? That will be crucial to figure out.”
Gangidine also plans to build an artificial hot spring in a lab aquarium using similar elements found in geysers. By introducing a super-saturation to the water, the excess silica will precipitate much the same way it does in nature. Then he can add trace chemicals associated with life and study what happens in a miniature world absent of life.
“To prove we found a biosignature, we have to prove the signature doesn’t occur without life,” he said.
If we find life on Mars, we can say maybe life is not that rare.
Taking the long view
Czaja’s NASA advisory committee will meet in October to decide where on Mars they would like to send the rover among the three preferred destinations. The rover is tentatively slated for launch in July or August of 2020, arriving on Mars about seven months later.
“NASA tends to like to go new places to push the frontier. Geologists like to go back to the same places over and over to ask new questions,” Czaja said.
The rover will collect samples in sealed containers for shipping back to Earth in a later mission. So it could be many years before geologists such as Czaja and Gangidine know whether their hunches about where best to look for life on Mars were correct.
Helping to frame a question that you may never live to see answered is one of science’s most selfless pursuits, Czaja said.
The Mars 2020 mission will not be a failure if scientists find no evidence of life. Quite the contrary, Gangidine said.
“If we find it, we can say maybe life is not that rare among planets,” Gangidine said. “But if we don’t find life in places that would be the most ideal and best preserved candidates, then maybe life is pretty rare.”
But if NASA does find evidence of life on Mars, that might suggest that sparking life from a primordial soup isn’t so extraordinary after all. And the first question will be how life on Mars compares to life on Earth, Czaja said. Was there a common ancestor?
“Maybe we’re all Martians,” Czaja said.
Any claim about the existence or absence of life on Mars will be subjected to worldwide scrutiny and skepticism. And researchers must be prepared to provide a wealth of evidence to fortify their findings.
“It’s not nearly enough to find something that looks like a bacterial cell,” Czaja said. “There are nonbiological things that could look like that. But if you have a cascade of traits — this and this and this added together — it’s hard to explain it any other way except for life.”
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