There are places on Earth that replicate conditions that existed when it was very young and life, as it were, was just starting out. It’s also speculated they give an idea of how life might exist on planets such as Mars.
You might imagine they are barren, rocky and hot desert landscapes such as the Afar Triangle in northern Ethiopia – it’s how other worlds are frequently depicted in science fiction movies.
But in fact, some of the places that offer the best template for life on other planets are almost impossible to view with the naked eye. Photographs reveal little or nothing about what makes them special.
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They are Deep Hypersaline Anoxic Basins or DHABs, and essentially (as their names suggest) they are massive reservoirs of extremely salty water deep down in our oceans and seas where there is very little oxygen.
One such DHAB or brine pool is in the Orca Basin in the north of the Gulf of Mexico. It covers an area of 123km2 – that’s about the size of the city of Leeds – and it has a depth of about 220 metres (but is itself at a depth of more than 2,000 metres).
The salinity in these pools can be 8-10 times that of the surrounding seawater, and as a result, there is almost no mixing between the two bodies of water. Partly, but not wholly, as a result of the salinity, there is very little dissolved oxygen in the water, giving them another name – “pools of death”.
It is said that any animal that is unfortunate enough to swim into these pools are poisoned by hydrogen sulphide and methane and then preserved by the extreme saltiness. They are sometimes compared to briny moons of Jupiter and Saturn.
But though the brine pool in Orca Basin is regarded as being a death trap for multi-cellular life, that doesn’t mean they are lifeless. In fact, they teem with microbes that have evolved to survive in the extreme conditions found in them.
Not only that, but the sediments preserve organic material because the elements that would normally destroy it – scavengers and decomposers that require oxygen to live – are absent.
So, what exactly does live in the death pool? Well, according to this research paper published in 2020, there are halophilic (which simply means an organism adapted to a salty environment) bacteria, as well as bacteria which instead of respiring oxygen to obtain energy, use sulphates instead.
There are also single-celled organisms called archaea, which are regarded as being in a completely different branch of the tree of life to both bacteria and eukarya, which includes all the multi-cellular life forms of the planet such as animals, plants and fungi.
These archaea include organisms that give off methane through metabolic processes and those that metabolise methane instead.
And all that salt that is dissolved in the brine pool? That comes from ancient salt deposits, known as the Louann salt, buried beneath the seabed of the Gulf of Mexico from 165 million years ago, and these deposits are gradually being exposed. Elsewhere brine pools are found in the Mediterranean and the Red Sea.
The oddity of life that lives in the Orca Basin brine pool fascinates scientists, and as a result, plans to use the basin as a place to test a controversial process for storing atmospheric carbon dioxide have been criticised.
Writing on the environmental news website Mongabay earlier this year, the deep-sea biologist Cray R McClain says a company called Carboniferous has been granted a licence to dump 20 tonnes of agricultural waste in the basin.
The idea is that the low oxygen, anoxic environment will stop this waste from decomposing, thereby locking that carbon (which the plants took from the air when photosynthesising) away for good.
There are all sorts of things that could go wrong. “Introducing a large pulse of organic material into a system like this could trigger cascading biological changes that are difficult to predict and impossible to reverse,” McClain says.
These changes could actually result in the area no longer being anoxic at all. It’s not a solution to man-made carbon emissions, and we should leave this unique area alone, McClain concludes.
