Complex sentence: Humans have created a wide range of new species, and varieties within those species, of both domesticated animals and plants in a very short geological period of time, spanning only a few tens of thousands of years, and sometimes less.
Split into simpler sentences: Humans have created a wide range of new species, and varieties within those species, of both domesticated animals and plants. This has been achieved in a very short geological period of time, spanning only a few tens of thousands of years, and sometimes less.