It had air, water, game, forest, and immediately arable land (cleared by people who had died in imported pandemics). It even had gravity. What does Mars have be

It had air, water, game, forest, and immediately arable land (cleared by people who had died in imported pandemics). It even had gravity. What does Mars have besides caustic dirt? We have no valid reason to assume a pregnancy could be carried to term in Mars gravity.