Doesn't even have to be deep beneath your feet, a square meter of average soil contains thousands of species. In that square meter you can have 10,000,000,000

Doesn't even have to be deep beneath your feet, a square meter of average soil contains thousands of species. In that square meter you can have 10,000,000,000 baceria, 1,000,000,000 protozoa, 5,000,000 nematodes, 100,000 mites 10,000-200,000 individual Collembola, 10,000 rotifiers and/or tardigrades, a few thousand larger insects/spiders/diplurans and dozens of slugs & snails. That's within a few inches of the surface. A cubic meter would increase that considerably for stuff like bacteria and protozoa. This is my biggest issue with terraforming another planet. It isn't the massive geo-engineering, it's adding all of that biodiversity and spreading it over a regional or global scale... even transplanting an initial acre would be a daunting task.