From Wikipedia entry regarding the Toba catastrophe theory:

“Genetic evidence suggests that all humans alive today, despite apparent variety, are descended from a very small population, perhaps between 1,000 to 10,000 breeding pairs about 70,000 years ago.* 

*Note that this is an estimate of ancestors, not of total human population. Isolated pockets of humans who eventually died out without descendants may have also existed in numbers that cannot be reliably estimated by geneticists.

70, 000 years ago is not as long ago as it sounds. The oldest living tree is around 10,000 years old. It’s a Norway spruce that’s located in Sweden. They aren’t counting the bark of the tree (it’s around 600 years old) just the roots.