Now Reading
The Limits of Life In Earth’s Most Extreme Environment

The Limits of Life In Earth’s Most Extreme Environment

Dallol is kaleidoscopic when seen from above.

The science is in: Lava It is molten but not for human life. It flambés it to death. However, microbes can thrive even in conditions that would be unimaginable for most animals. This is also true for a large portion of the East African Rift. It has watery pools that are home to all types of life, and is situated between jagged lava flows still under a thin crust.

And then you’ve got Ethiopia’s Danakil Depression.

Danakil lies more than 330 feet below the sea level in the larger Afar depression, which is the tectonically active zone where the African plates have been slowly splitting over the past 20 million years. It is protected by a volcanic mound that runs along its coast. “But when the sea level was higher” in the distant past, says Christopher Jackson, an expert in geologic basins at Imperial College London, “there used to be marine waters in the Danakil Depression.” Ancient coral reefs, marine terraces, and salty minerals stand as memories to the watery land this once was.

Dallol is kaleidoscopic when seen from above.
Dallol is breathtaking when seen from the sky. Ignacio Palacios/Getty Images

It is considered a hostile area today. This 160-​mile-​long bowl has daily average temperatures of 94 degrees Fahrenheit, making it one of the most sun-​scorched places on Earth. Danakil receives only four inches of rain each year. You can also find the volcano Dallol within Danakil, flanked with numerous hydrothermal pools and ponds. It is a multicolored hellscape. Volcanic chemicals brought up by the East African mantle monster—the plume of super-heated magma that is sundering the continent from below—decorate the waters in vibrant greens, luminous oranges, milky whites, and sickly yellows. The air smells of rust, eggy sulf, and acrid chlor. If you approach the tiny mineralized mounds that loom over the wheezing pool, these viscous vapors will bite your nasal cavities.

Purificación López-​García, a microbial diversity expert at the French National Center for Scientific Research, has worked around Dallol in temperatures exceeding 122 degrees Fahrenheit. You have to drink water constantly and move very slowly so you don’t overheat. Working here and in the surrounding region was, she says, “the most extreme experience I had in my life.” Felipe Gómez, a microbiologist with the Astrobiology Center in Madrid, Spain, says that Dallol looks very beautiful, but it is incredibly hot and full of death. “Some birds see water and dive down [to drink] and die over there,” he says. “It’s possible to see some of the small pools surrounded by birds that have died. Yeah, it’s horrible.”

An Afar man looks out over toxic pools in the Danakil Depression.
Afar man watches over toxic pools of the Danakil Depression. Eric Lafforgue/Art in All of Us/Corbis/Getty Images

However, the old adage says that water is life. As long as there is water and some chemical compounds that can be used to make energy, certain species of microbes—​extremophiles—​can make Dallol their domicile. Amazingly, some microbes can live in combination of both of these extreme environments, making them polyextremophiles. Showoffs.

Dallol is the same, at least to a certain extent. Microbes that are hardy have evolved to withstand extremely high temperatures. Some microbes can also survive in extremely salty environments. Others thrive in very acidic (low-pH) environments. “We normally say that pH is zero, because we have no probes adapted to measure a negative pH. In theory, a negative pH doesn’t exist,” says Gómez. However, there are some pools that have a very low pH. Yet, life is a good thing.

Salt mounds grow where hypersaline water emerges from the geothermal field.
Salt mounds form where hypersaline water is released from the geothermal fields. Gunter Fischer/Education Images/Universal Images Group/Getty Images

Dallol contains hyperthermal pools, hypersaline and hyperacidic lakes. Because of its unusual and large volcanic fuel source, Dallol has bodies of water that meet all three criteria, making it an attractive place for microbiologists. Life flits about in some of these watery pools, but others, says Gómez, are completely sterilized. Sometimes the extremes are just too extreme for human life. Sometimes, the pools are so contaminated with chemical compounds that there is not enough water for microorganisms.

“In every extreme environment where I have been, if I found water, I found life,” he says, speaking of his adventures to both the North and South Poles, the Atacama Desert, and so on. “The only exception is here at Dallol.”

Barbara Cavalazzi is a geobiologist and an astrobiologist at University of Bologna. She says this is the ideal place to study astrobiology or the search for life beyond Earth. If life is found in these pool, it means that it is living within the limits of biology on our planet. If life is not present, then perhaps we have discovered conditions that prevent any life from being created. This concept may also apply to other worlds. That makes finding where the limit lies in Dallol—​arguably the most otherworldly consequence of the East African Rift—​a scientific endeavor with profound consequences.

A water-filled eruption crater at Dallol.
Dallol’s water-filled eruption crater. Getty Images/Guentergun

In 2019, Gómez and his colleagues published a paper that looks to have pushed the limits to life even further into the unfathomable beyond. A few years back, while using the Danakil Depression to calibrate a scientific instrument that would ultimately end up on NASA’s Curiosity rover on Mars, they poked about in the pools around Dallol and found fatty acids, the sort that can be found in cells. They found tiny, round structures in mineral deposits, after ruling out contamination by tourists, scientists, and animals. They concluded that these were bacteria cells.

See Also

This was a big surprise. It was a huge surprise that life on Earth could be found in such a combination of hyperacidic, hyperthermal and hypersaline environments. It is possible for something to survive in this pool. Stranger still, this kind of microbes has never been seen in such extreme environments. Gómez and his team are currently trying to unravel the biophysical mechanisms that permit the microbes’ survival, work that is truly at the leading edge of microbiology.

Later that year, López-​García and her colleagues published a paper that indirectly ran contrary to this discovery. They found that similar pools were filled with all three extremes. They discovered that too much salt and acidity was a problem for life. Magnesium salts in high concentrations could break down chains of molecules and destroy protective membranes around cells. “They suck up the water” that cells need, she says—​a fatal blow for microbes. The team also suggested that the tiny grains found in the pools resemble cells but are only mineralogic mimics. This can be misinterpreted to mean that they are evidence for life.

The Danakil Depression is part of the East African Rift, where the continent is slowing splitting apart.
The East African Rift is where the continent is slowly splitting apart. Courtesy David Moreira (CNRS)

Gómez remains upbeat and confident. He says that he wouldn’t have believed the paper’s results a few years ago. However, the limits of life seem to get further away with each passing year.

However, everyone agrees that Dallol’s only way to function is because of East Africa’s volcanism. Volcanoes provide heat and chemicals that microbes can use for energy. Add water to make it a home for curious little creatures.

Volcanoes are dangerous. “But from a scientific perspective, it’s quite the opposite,” says Gómez. “The origin of planet Earth is volcanoes.” And no one knows for certain, but these sorts of habitats are probably like those that first gave rise to life, from which every living thing today has descended.

View Comments (0)

Leave a Reply

Your email address will not be published.