In the early summer of the year 2000, in a laboratory in West Chester University, Pennsylvania, a microscopic bacterium came out of a state of suspended animation and made itself known to the world of science. This remarkable bacterium had shut itself down when the lake it was living in had become super saline due to evaporation and had lain dormant until conditions improved to such a degree as that it could continue living as before. What is even more remarkable about this return to animation is that Bacillus 2-9-3¹ had demonstrably been in suspended animation for 250 million years.

That's a long time...

250 million years is a very long time indeed - almost beyond the scope of human comprehension. 250 million years ago the dinosaurs were yet to walk the earth. At that time there was only one continent. In fact, in the intervening period since isolate 2-9-3 put itself to sleep² the entire Milky Way has rotated once around its central point.

How do they know it is that old?

Scientists were able to date the salt crystal in which the bacterium was found by reference to the invertebrate fossils in the strata overlying the deposits and by radiometric age measurement of minerals taken from the same source. Careful examination of the salt crystals showed none of the characteristics which could be expected if the crystal had liquefied and re-crystallised during that time.

How do they know it is not just recent contamination?

Bacteria are absolutely everywhere³ so the threat of samples being contaminated is very real. To reduce this risk to a scientifically acceptable level, the outside of the salt crystal was washed in strong alkali and then strong acid solutions. The scientists (Russell H Vreeland, William D Rosenzweig and Dennis W Powers) put the probable risk of contamination at less than 1 in 1,000,000,000.

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¹ This is its designated name which will be changed when its relationship with already classified bacteria is known.
² This term is used loosely - in fact suspended animation is more akin to death than sleep.
³ There are thought to be as many bacteria on and in the human body as there are human cells.