In the heart of the Horn of Africa, the Danakil Depression is one of the most remote, inhospitable and least-studied locations in the world. It lies over 330ft (100m) below sea level in a volcanic area in north-west Ethiopia aptly named “Afar”. It is part of the East African Rift System, a place where the Earth’s internal forces are currently tearing apart three continental plates, creating new land.
The violent landscape is arguably the hottest place on the planet, and one of the driest. The temperature regularly reaches 45C (113F). It rarely rains, but seas of molten magma ooze just beneath the crust’s surface. There are two highly active volcanoes: one of them, Erta Ale, is one of only a handful of volcanoes to have an active, bubbling lava lake at its summit. The area is also littered with acid ponds and geysers, and features a deep crater called Dallol.
The vibrant colours are a result of rain and seawater from the nearby coast being heated by magma and rising up. The salt from the seawater reacts with the volcanic minerals in the magma, creating dazzling colours. In the hottest and most acidic pools, sulphur and salt react to form bright yellow chimneys. In cooler pools, copper salts create bright turquoise.
The hot and dry climate means that few plants or animals can survive there. The Dallol site itself is unpopulated, but the nomadic Afar people have settled nearby in a semi-permanent village called Hamadela.
In short, Danakil looks like an alien planet and is completely unique on Earth. It is somewhat similar to active hydrothermal zones like Yellowstone in the US, but it is much hotter and its waters are much more acidic. In fact, Danakil’s waters have an average pH of 0.2, which is almost unheard-of in any natural setting.
We also know much less about Danakil than Yellowstone. However, this is set to change. Since 2013, a team of scientists has begun studying the region. They are from Europlanet, a consortium of research institutions and companies that researches areas of Earth that could serve as analogues to Mars.
Barbara Cavalazzi from the University of Bologna in Italy is part of the team and has been conducting expeditions in Danakil since 2013. “The environment is very extreme,” she says. “On average, the temperature over there around lunchtime can reach 48C (118F). One time we measured 55C (131F).”
In the Dallol crater, the geothermal activity increases the temperature even further, so the brine water reaching the surface is about 100C. As well as the sweltering heat, the scientists have to cope with toxic hydrogen sulphide gas, not to mention chlorine vapor burning their airways and choking their lungs. They must all wear gas masks to work there for any period of time.
The first few expeditions in 2013 were simply focused on figuring out how to work in Danakil. “You can’t bring a fridge or chemicals to store samples in, so you need to think very hard and plan what you are going to do,” says Cavalazzi.
In spring 2016, the researchers finally began collecting samples from the hot springs and pools, hoping they would contain life. They also measured the temperatures and pH of the pools. They returned in January 2017 to collect more samples.
In March 2017, Cavalazzi’s lab and their colleagues found life in Danakil, after they managed to isolate and extract DNA from bacteria. They found that the bacteria are “polyextremophiles”, which means they are adapted to extreme acidity, high temperatures and high salinity all at once. It is the first absolute confirmation of microbial life in the Danakil acidic pools.
In as-yet-unpublished research, the team found two separate forms of bacterial life in two separate areas of the site: the salt springs and pools inside the Dallol crater, which are characterised by bright colours, acidity and boiling temperatures; and in a small lake outside the Dallol crater.
The lake is not as hot as the salt springs, reaching a mere 50-55C, and the water is also different: it is still salty, but less acidic with a pH of around 2. The water is rich in carbon dioxide, which is released by the volcanic activities below.
“The lake is known by many different names,” says Cavalazzi. “The local people call it ‘Gaet’Ale’ or ‘Arrath’. Some call it ‘oily lake’ or ‘yellow lake’. Other people have named it ‘killer lake’, because when you work around it and look around you can see a lot of small insects and birds lying dead nearby. They probably arrived there and drank some water, but what actually killed them was the strong emissions of carbon dioxide.”
Because carbon dioxide is heavier than normal air, it sinks to the ground, so when small creatures like birds breathe the area just above the lake they suffocate. For humans, who tend to be rather taller, it is not so dangerous. But any organism that stays within 12in (30cm) of the water will find itself breathing in too much carbon dioxide, and die.
One of the scientists’ discoveries looks set to establish a new record.
The team found life in a pool where the acidity was measured as zero pH. That pool is the most acidic place where life has been found on Earth. The previous record was in the Rio Tinto, a river in Spain that has a pH of 2.
Water becomes acidic when it contains a lot of positively-charged hydrogen atoms. Most living creatures cannot cope with extreme acidity, because the charged hydrogens interfere with the structure of special proteins called enzymes, which orchestrate all of the vital chemical reactions inside cells.
High temperatures can also damage enzymes, and break apart the chemical bonds that hold DNA and cell membranes together. Meanwhile, high salt levels can make water rush out of cells, causing them to shrivel up into dried-out husks.
Whatever the case, the scientists’ findings may help us understand how life could have arisen on other planets and moons.
“On Mars, you have mineral deposits and sulphate deposits similar to those seen in the Danakil Depression. You also have active brine flowing periodically,” says Cavalazzi. So by studying in which extreme Earthly environments life can survive, and how it does so, we can start to figure out which regions of planets like Mars might be habitable.