Río Tinto: A Terrestrial Analogue for Life on Mars?
Forty years ago NASA launched the Viking program- often considered to be the first astrobiological mission devoted to the search of life on Mars. After this mission, it was concluded that life had little chance of survival on the Red Planet due to extreme conditions experienced across the surface by the exploratory probes.
Important advances in microbiological science have since challenged this pessimistic viewpoint. Microorganisms known as ‘extremophiles’ are now found to flourish in some of the most uninhabitable environments on Earth, allowing us to appreciate how robust and adaptable life is and strengthening the evaluation that it could indeed exist beyond Earth.
The Río Tinto (‘Red River’) which runs through Spain is a well-known example of extreme conditions on Earth. The river has such a high concentration of soluble iron that the water runs a deep red colour and tests at an acidic pH (<3) along its entire 92km length. The river is polluted with strong concentrations of heavy metals from mining processes (which began as far back as 3000BC) and is recorded as one of the most polluted streams in the world.
Despite all of this, the river tests remarkably high for microdiversity, acting as an ecological niche for at least 1300 difference species of algae, fungi and bacteria- 80% of which correspond with the iron cycle. In fact, the high levels of soluble iron help absorb harmful UV rays, protecting organisms under the surface. Other unique biological arrangements throughout the Río Tinto demonstrate the complex, multicellular systems which can develop even in extreme conditions.
More recently, the 2004 NASA rover ‘Opportunity’ was sent to explore Meridiani Planum and identified iron units of haematite, goethite and jarosite. The composition of rocks collected match well with the water chemistry found at Río Tinto, with jarosite, in particular, being known to form in very acidic conditions.
Similar lithological units to those found on Mars are also found in the Tinto basin system and, as such, give Río Tinto the possible status of geochemical and mineralogical terrestrial analogue to the geomicrobiological processes which may have driven the generation of abundant iron oxides on the surface of Mars, giving the planet its unique red colour.
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