By Ashley Strickland, CNN
Near the top of the Poás Volcano in Costa Rica is one of the most acidic lakes on Earth, bright blue and full of toxic metals.
The harsh conditions of Laguna Caliente, where temperatures can fluctuate between 100 degrees Fahrenheit (38 degrees Celsius) and 194 degrees Fahrenheit (90 degrees Celsius), is where a few lucky scientists travel to learn more about Mars.
Frequent phreatic eruptions occur when groundwater is heated by volcanic activity, releasing explosions of ash, rock, and steam.
Yet microbes have found a way to live in this environment, one of the most hostile on our planet, according to multiple studies of the lake and new research published last week in Frontiers in Astronomy and Space Science.
Although the diversity of life in this lake is not high, it has managed to adapt and persist in multiple ways.
“Our discovery shows that life persists in Earth’s most extreme environments,” said study author Justin Wang, a graduate student and research assistant at the University of Colorado Boulder.
“It’s hard to imagine anything more inimical to life than an ultra-acid volcanic lake with frequent eruptions,” Wang said. “The low biodiversity associated with numerous adaptations and metabolisms in our sample suggests that the lake hosts highly specialized microbes for this type of environment.”
This otherworldly environment could hint at how life might have existed on Mars billions of years ago and reveal new places to look for evidence of ancient life on the Red Planet, researchers say.
A tale of two lakes
The two crater lakes near the top of the volcano, both formed after craters filled with rainwater, couldn’t be more different from each other. An inactive crater contains Lake Botos, which is surrounded by tropical vegetation. The active crater is home to Laguna Caliente, which contains liquid sulfur and iron. Gases from the lake create acid rain and acid fog, harming nearby ecosystems and irritating the eyes and lungs of intrepid explorers.
Researchers conducted active field studies on the lake in 2013, 2017 and 2019. While results from the 2019 excursion are still awaited, it is a trip Wang will never forget.
The Poás Volcano, located in the middle of Costa Rica’s rainforest, erupted most recently in 2017 and 2019. The area immediately around the volcano is devoid of life due to the toxic gases it releases.
Wang and his collaborators hiked to the volcano in November, a month after the crater lake reformed. They were aware of where they were stepping in the loose soil caused by the acidity breaking down the surface material. Parts of the lake boiled over and volcanic openings called fumaroles spewed hot sulphurous gases.
“When I went to Poás Volcano it was after over a year of magmatic eruptions and only a month after the lake had reformed and it was deemed safe enough to return to the surface of the crater lake,” said said Wang. “The lake itself is bubbling and dynamic. Getting even closer, you can smell the strong smell of sulfur, which remained on the clothes I wore to this day. Worse still is the smell of hydrochloric acid, which tastes sour in the air and stings the eyes.
Around the lake are puddles of boiling water and acid, and Wang felt the heat of the volcano through the bottom of his shoes near the shore of the lake.
The researchers took samples from the lake, as they had done in 2013 and 2017.
“It’s a very intense and exciting experience to taste the lake,” Wang said. “I am very lucky to be one of the few scientists in the world to have been able to visit this environment.”
Living on the edge
In 2013, researchers determined that Acidiphilium bacteria live in the lake. These microbes are often found in acid mine drainage as well as hydrothermal systems, such as Laguna Caliente. Acidiphilium bacteria have several genes that allow them to adapt to survive in different environments.
Other eruptions occurred at the site before the team returned in 2017. After collecting more samples, the researchers found that there was slightly more biodiversity among the bacteria in the lake than expected. What’s more, their DNA sequencing revealed that the Acidiphilium bacterium has evolved ways to convert elements like sulfur, iron and arsenic to create the energy it needs to survive.
“Between 2013 and 2017, there were numerous phreatic eruptions that brought toxic metals, extreme acidity and heat to the lake, but we still saw some of the same microorganisms in the same environment,” said said Wang.
About a month after the team collected samples from the lake in March 2017, the Poás volcano erupted with magma. The force of the explosion threw boulders more than a mile from the site, spewed lava, drained the crater lake and released an ash plume about 12,000 feet above the crater on several occasions, has said study co-author Geoffroy Avard, a volcanologist at the Volcanological and Seismological Observatory of Costa Rica.
“We would like to characterize how life reclaims this environment,” he said. “A main hypothesis of our study is that life in Poás Volcano is able to survive on the fringes of these extreme environments. We would therefore like to sample not only the crater lake, but also the shoreline, connected groundwater systems and anywhere where life could be accommodated nearby.
The search for life
Genetic adaptations discovered by Wang and his colleagues during their study suggest that life could have survived in hydrothermal environments on Mars, just as it does in some of the most extreme places on Earth.
Hydrothermal systems provide heat, water and energy, all necessary for the formation and evolution of life. While previous Mars exploration has looked at ancient water sources like craters and rivers, researchers believe ancient hot spring sites are another key target in the search for extraterrestrial life.
“These spots aren’t hard to find since early Mars had creeping volcanism and abundant water near the surface,” said study co-author Brian Hynek, an associate professor in the Department of Geological Sciences at the University. University of Colorado at Boulder and research associate at the university’s Atmospheric and Atmospheric Research Laboratory. Space physics, by e-mail.
“In fact, we have discovered many ‘dry Yellowstones’ across Mars, based on sulfur-bearing mineral signatures detected from orbit,” he said.
The NASA Spirit rover even encountered a volcanic vent when it explored Mars between 2004 and 2011, Hynek noted.
“The crater rim of Jezero Crater, where the Perseverance rover is now, is a location that likely exhibited hydrothermal activity due to the crater-forming impact that occurred, so I’d be curious to see what Perseverance finds results when it gets there,” Wang said.
Research to understand the tiny organisms that live in extreme environments is changing the way scientists think about the limits of life, whether in an active volcanic crater lake or along hot hydrothermal vents on the ocean floor.
While this helps researchers shift their thinking about how life might exist in harsh conditions on other planets, Wang cautions that scientists shouldn’t be too “Earth-centric” in their approach. Life on Earth is usually found in the presence of water, but the existence of water on Mars was much more limited and episodic in the past, he said.
“I think we need to change the way we think about life on other worlds,” Wang said. “We need to consider the unique geological histories of our extraterrestrial environments and put them into context with what we have here on Earth. If rivers were unstable on Mars while hot springs were common, then perhaps life in hydrothermal environments is the most likely place where life could have existed.
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