Terraform Mars
First we must start from the basis that there is no life present on Mars, because we still cannot affirm that life exists or does not exist on Mars, we would need to examine what is under the surface of the red planet, where we have recently known that there are large reserves of liquid water, large ocean-sized reserves, which is quite normal, it is within the logic, keep in mind that if Mars had water in the past, which we know well, it must have had a large ocean in the northern hemisphere and then lakes, seas, rivers, etc. that water also filters into the interior of the planet.
The seas are not isolated and closed bathtubs, they filter the water that we see, the water that we see from a sea, the Mediterranean is only a small part of the whole water that is also below that has been filtered, beneath the surface of the Earth there are large reserves of water and that also happens on Mars, on Mars those oceans, those lakes were lost a long time ago, but the water that remained below the surface is there and much of that water is in a liquid state because the interior of Mars is still hot, it is not as hot as the core from Earth because Mars is a smaller planet, but it still keeps a lot of heat.
If life emerged on Mars billions of years ago, something that we still cannot deny or affirm, it did arise, because also in that same period where Mars had water and the essential components for life to form was the same moment in which life emerged on Earth, it is very possible that these microorganisms and emerged colonized the underground aquifers just as happens on our planet and that they stayed there evolving, without needing to come to the surface, so it is a possibility still open, but we are going to work with the idea that There is no life present on Mars, because if it existed, even if it is down there, several kilometers deep, it could be a pretty big problem and I am not talking right now about moral ethics, about these things about planetary genocide and these stories, no, I am talking about how we, our microorganisms can contaminate those living beings, Martian microorganisms, but those Martian microorganisms can also contaminate us, after all they are on their planet and if they exist and have evolved down there, they have evolved for billions of years. in extreme conditions, so they do exist and some of them end up filtering into one of those colonies like the ones Elon wants to create. More may find that suddenly he is in a bacchanal in a paradise for him to expand and do what a microorganism does, reproduce and eat.