The impact of human activities on Earth has served to propose that we are initiating a new geological time, the Age of Humans, or Anthropocene. Can we start thinking about quantifying the human impact on Mars?
Since when is there an obvious impact on the geological record of the Earth caused by human activities? According the committee of geologists in charge of studying and defining the case, from the middle of the XX century: it would have been then when the Anthropocene began, the current geological period, after the Holocene. The Anthropocene is not yet a formally defined geological unit, but the term has been generalized in popular and scientific literature, and in the media, since it was popularized in the year 2000.
During the Anthropocene, a large number of processes and geological conditions on Earth would have been profoundly altered by human activities. The impacts of humans would be beginning to leave their mark on the stratigraphic record, in a univocal way, with a global extension, with a high preservation potential and with a synchronous base.
For a few decades, and for the first time in history, the impact of human activities can begin to be quantified in other bodies of the Solar System. And the case of Mars deserves special attention. So far, the exploration of Mars has been exclusive task of robots, which have left a barely perceptible impact on its surface. But a fundamental change is already under way: the arrival of humans to Mars is anticipated for within less than two decades, and the presence of astronauts could inaugurate a time of lasting human effects on Mars. Three will be the most immediate and profound impacts.
The first impact, and potentially the most obvious and significant, is the microbial contamination, which will be inevitable from the moment an astronaut sets foot on Mars. The human stays on Mars for months will require the use of modules and rovers, as well as the provision and transportation of water and food, a continuous supply of air, storage and processing of waste and excrement, and a long etcetera. The risk of contamination will be very high, with the risk of affecting the planet in a global way.
In addition, it is possible that the first settlements occur at least partially below the surface, in caves or caves, or in small local excavations, because being underground will give the astronauts additional protection against radiation and extreme thermal fluctuations of the surface . The disadvantage of this human strategy of re-colonizing a planet beginning with inhabiting its caverns is that the natural conditions hostile to terrestrial life on the surface will not act on bacterial communities that parade with astronauts underground, and the risk of biocontamination of Mars will be greater.
A second impact will take place shortly thereafter, by the time we start find and use natural resources in situ. The extraction and processing of primary materials to obtain resources with which to feed our astronauts and our machines, will forever transform the surface of Mars. We will start with local erosions of the regolith, small avalanches and ground collapses, and the process will continue with the modification of large areas when we begin to dig mines, pile up sediments and flatten hills.
This second impact will also help to amplify the first: by extracting resources, we will contribute to generate new zones where our accompanying microorganisms can thrive. For example, if we drill the surface to explore a possible underground aquifer, our microbial stowaways will travel with us through the Martian subsurface.
And the third impact Immediate will be the introduction of pollutants. For a Martian base to be fully operational, providing at least four astronauts with shelter, a source of energy far greater than that required by the current robotic exploration will be required. To supply these enormous needs, the use of nuclear generators will be almost inevitable on a planet so far from the Sun. And accidents occur, both in transport and in the use of generators.
In short, the technological deployment that will make human life possible off Earth will be so enormous, and the alterations of the Martian landscape to adapt it to our needs will be so profound, that we will change the skin of Mars forever. We have an example on our own planet: Antarctica, which shares certain similarities with Mars in terms of climate, terrain and degree of isolation. Although the human presence in the frozen continent is largely limited to scientific research, and there are well-defined policies for the conservation of the environment, the effect of the Anthropocene is already visible in Antarctica.
Predict and understand the alterations that humans will produce on Mars It is key to interpret and mitigate the anthropogenic impact on the planet. We have the time, resources and intelligence to do it in an orderly manner.