These questions have been a fascinating mystery since the 19th century. While scientists search for signs of biosignatures outside Earth and study extreme environments on Earth to try to understand how life evolved on Earth, there is still much work to do. The further back in time we go to look for fossilised biosignatures, the less clear the rock record of life becomes. Even harder it is to search for evidence of life on Mars with the current technologies. However, despite the current extreme conditions, Mars was more similar to Earth than any other known planet in the outer space, and in fact, remains so to date.
It is known that Mars, well over 3.5 billion years ago, may have harboured primitive microbial-life forms, when flowing water and volcanoes promoted the formation of hot springs. On Earth, hydrothermal habitats always contain extremophiles, or organisms capable to adapt to the extreme conditions. Early Earth also was hotter than today, the sea contained great amounts of dissolved silica due to a lack of planktonic organisms like today that use it for their shells. Thus, 2.5 billion years ago the oceans on Earth were warm and able to precipitate silica as a preserving medium for early life forms in a way not found on Earth today, except in hot springs. So could microbial life be preserved on Mars in the same way it is preserved on Earth? Or could it be present in the subsurface today? Until a manned mission to Mars is feasible, we still need Martian analogues here on Earth that comprise not only similar extreme environments, but also evolutionary history to mimic the conditions under which early life may be preserved for millions of years.
The Rotorua area, in New Zealand, is such a Martian analogue and can give us insight in the quest to answer these questions. The area is one of the most interesting places for finding extreme microbial-life forms that may provide unique and critical information on possible Martian life. The hot springs in Rotorua are typically mineralising, trapping biota in silica, iron or carbonate discharging from the hot springs themselves, therefore providing the perfect conditions for life to be preserved and protected for millions of years, leaving behind a unique biosignature of past life.
This is a question astrobiologists don’t think is absurd at all. The New Zealand Astrobiology Network is organising the Australasia Astrobiology Meeting 2018, a conference and 3-day expedition in the spectacular Taupo Volcanic Zone parks and hot springs to explore extreme environments and look for microbes that thrive in hot and acidic conditions. These hot spring deposits are now recognised worldwide as paleoenvironmental evidence for extreme life and analogues for Early Earth and Mars habitable environments. So if life ever existed on Mars, it is likely it would have been similar to the organisms in Rotorua, and been fossilised in the same way. Thus there is a need to understand how the most primitive braches of life´s phylogenetic tree (the extremophiles in hot springs) became fossilised and incorporated into the geological record, as these chemical signatures of life may be the best evidence that life on Mars once existed.
The team will visit hot springs of varied fluid compositions, the Au-bearing Champagne Pool or the picturesque microbial mat-draped sinter terraces of Orakei Korako, in between others. The huge diversity of hot springs in Rotorua is also an advantage, both alkaline and acidic hot springs are scattered in the area, which is very important to study different types of extremophiles. The goal of the meeting and expedition will be to understand when and where life may have evolved on a hotter early Earth, whether life ever was, or still is, on Mars, the composition of the Archean atmosphere, and the setting for the origin of life.
Rotorua is, in effect, what we call an analogue for early Martian life. Even if it is not a perfect representation of early Mars, Rotorua represents an open window through which we can observe Mars in the past, and this opens a wide range of questions and mysteries regarding the habitability of the Red Planet. While, for now, these questions are still uncertain, field research in places like Rotorua are of extreme importance to advance our knowledge of the limits of life on Earth and possible microbial life on Mars.