Mono Lake is believed to have formed at least 760,000 years ago and is thought to be a remnant of a much larger and older lake that once covered a large part of Nevada and Utah. It is estimated that at its peak (during the most recent ice age) the lake may have been around 270 m deep. Old shore lines which show the previous extent of the lake (known as strandlines) can be seen above the town of Lee Vining and along the hills to the northeast of the current lake.
Because Mono Lake now has no outlet to the sea, high levels of salt have become dissolved in the water over time and this has resulted in the lake becoming highly alkaline. Depending on the water level, the lake is typically seen to be two to three times more salty than the sea. Despite this high alkalinity the lake is still home to life and the most complex creature that resides within the lake is a form a brine shrimp.
Mono lake is of particular interest to astrobiologists as the extreme conditions in the lake give them the opportunity to study how life could potentially evolve and exist on other planets. In 2010 a study claimed that a form of bacteria had been found in Mono Lake that could use arsenic as one of its building blocks, in place of phosphorus - the current understanding of biochemistry being that all life comprises of at least the six elements carbon, hydrogen, oxygen, nitrogen, sulphur and phosphorus. If this claim was indeed true then the implication was that life could have potentially formed on earth (and other planets) in a radically different way to what is currently accepted.
These claims were unfortunately short lived however, with two further studies suggesting that the bacteria in question still needed to use phosphorus to grow, and that they did not break the current accepted model of biochemistry.
So it seems that Mono Lake may not be a home to “alien life” on Earth, but the search for a “shadow biosphere” will no doubt continue and the focus is likely to remain on extreme environments (like that of Mono Lake) where unknown forms of life may have carved out a niche for themselves.
Pictures of Mono Lake have also featured on Andrew May’s Forteana Blog
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