Making soil as the First Step in the Biological Terraforming of Mars

Building Soil. From the writer of The Terraformers' Toolkit. www.amazon.co.uk/dp/B09X6739P...
Warm and wait
The biological terraformers will have to wait while the atmosphere is built, radiation protection improved and surface temperature corrected, in case alien organisms appear. This period of physical terraforming could easily be 500 years or even longer.
Making soil
Mars’ regolith has poor water retention capabilities, so it would be dry even after the heaviest of rain storms. Turning regolith into soil is really critical to biological terraforming. But add organic material and life, and it could support the growth of plants and animals.
Extremophiles
The low temperature limit for bacteria, archaea, and unicellular eukaryotes is -20 C (-4 F). Lichens are able to grow down to -10 C (14 F). Higher plants and invertebrates can survive down to -70 C (-94 F), but for completion of their life cycles multicellular organisms have a limit of -2 C (28 F). Mars' temperatures average -63 C (-81 F) which is too low for these organisms to survive, grow and multiply.
Aerobic biological terraforming
Planet Earth will have to be searched for extremophile microorganisms which can survive the harsh conditions likely to exist on a partly terraformed Mars.
Antarctica
The Antarctic dry valleys are 1,332 kilometres (828 miles) from the South Pole and are the coldest places with life on Earth, which makes them the most likely source for the first life to be added to Mars. The winter temperatures in the Antarctic dry valleys can drop to nearly -65 C (-85 F). The maximum summer temperature in these dry valleys is about 10 C, but the average is about -20 C (-4 F). These regions are also very dry, the soil is very saline, and the organic content is very low. The species which have evolved to live in Antarctica have developed under very cold, dry, nutrient-poor environmental conditions, which are likely to change in the future as global warming is increasing temperatures faster at the Poles than at the equator. Some species may survive, whilst others may not.
The best way for organisms to spread across the Antarctic dry valleys is to have small seeds, spores or vegetative fragments which are easily lifted into the air by wind and storm. To survive, most species protect themselves in Antarctica by either growing under the surface or inside rocks. This allows them to maintain a slightly higher temperature than the outside environment and to retain access to liquid water. The first colonists are microbes such as bacteria, fungi, yeasts, algae and cyanobacteria which start to bind the mineral particles together, and begin to change mobile sands and gravels into true soils. Early colonist species start to retain water in the soil and accumulate a reservoir of seeds, spores and organic matter.
Organisms which are able to hide in or under rocks or in the soil have no difficulty surviving conditions which would kill any living on the surface. Together, these species are likely to be ideal first choices for terraforming Mars if they still exist.
In the Antarctic, lichens and algae may begin to form stabilising crusts or rafts on the soil which grow during summer, but can be blown away in winter. The wind-blown pieces act as sources of seeds, spores and vegetative material to start new rafts in other places in the Antarctic dry valleys. If these rafts are able to survive winter, they can be further colonised by more lichens, mosses, liverworts, small grasses, low-growing herbs, flagellated protozoa, nematodes, rotifers, springtails, mites and tardigrades.
Antarctic life forms have several key talents which should help future Mars terraformers. Firstly, they can tolerate extended low light periods as an Antarctic winter lasts for at least 6 months. Secondly, many can be frozen and reanimated with no ill effects. These means that they could be frozen in the Antarctic, transported to the launch pad, and remain frozen on their long 6 to 8 month trip to Mars. Those species which could not be frozen, like mites and springtails, would have to be transported in living, non-frozen form, and kept alive on their long journeys.
Making soil will be the most lengthy and difficult phase of biological terraforming, but terraforming cannot be done without this step. These species and others from Antarctica are the most suitable for early terraforming of a cold planet, but they are also the most vulnerable to extinction as our climate warms. Unfortunately, there are no alternatives, as nowhere else on Earth is as cold as the Antarctic. Therefore, they will need to be kept in living form in cold storage 'microorganism zoos', frozen in 'frozen arks' and have their DNA sequenced in the hope that they can be reconstructed when our descendants are ready to start adding life to Mars or finding ways to decrease Earth's temperature.