There's a place in Antarctica called Blood Falls.
It is named that because while most of Antarctica is white snow and the odd exposed rock, this place occasionally spits out a red liquid. The liquid turns out to be high contents of rust.
Underneath it is a lake. About two million years ago snow covered up the lake completely, sealing it off from the rest of the world. Before that happened it was teeming with microbial life, as most places on Earth are. Now, after having been cut off from oxygen for two million years, it is... still teeming with microbial life!
When investigated, it turns out that these microbes no longer use oxygen! They have instead evolved to metabolize using sulfur! This is basically an alien ecosystem!
This is a great resource for biologists who want to investigate what life might be like on other planets where there is no oxygen. For us laypeople though, it's just an example of how resilient, how tenacious Life can be.
(Via Bad Astronomy)