The terrestrial environment
Two principal factors have brought about the impoverished flora and fauna. The isolation of the Antarctic and sub-Antarctic regions from other continental land masses has created a sea barrier to immigration by plants and animals, and only ten thousand years ago the region was even more heavily ice-capped and inhospitable.

The second factor is the harsh weather, particularly the cold summer, which prevents the establishment and growth of all but the hardiest plants. If vertebrate animals could find their way here, the short slow-growing vegetation would be insufficient to support most herbivores, and consequently no carnivores could survive; seabirds and seals would be available as food for only part of the year, because of their patterns of migration.

Antarctic terrestrial life, excluding a few species of snow-dwelling bacteria and algae, is restricted to areas which become snow-free for a few months in summer. Such land is mostly in coastal areas and offshore islands where the warming influence of the adjacent ocean creates a slightly more hospitable environment; this applies also to the more alpine sub-Antarctic islands. In many potentially suitable areas vegetation is excluded by dense colonies of penguins or seals.

Vegetation requires a regular supply of water during the summer. This, together with the nutrients dissolved in it, permits limited growth for a few months, rarely longer even in the more northerly regions. Because of warming by the sun's radiation, temperatures at plant level often exceed 20 degrees C. even when the air temperature is well below the freezing point, thereby creating a relatively favorable environment for plants and invertebrate animals.