According to findings announced at the recent Goldschmidt geochemistry conference, some bacteria, viruses and fungi that live up to 2.5 km below the ocean floor are extremely long-lived, and these findings give hope in the search for extra-terrestrial life.

Just how long-lived are we talking? Hundreds of years would be impressive, thousands would be amazing, but estimates for the age of these single-celled organisms are currently up to 100 million years old. The ocean-floor sediments they call home — which were used to find out how old they are — settled to the seabed long before Tyrannosaurus Rex ever showed his face on land!

How did these life forms live for so long? Apparently, by eating very, very slowly. There isn't a lot of food in the muck at the bottom of the ocean, so the microbes that live there have to make it last. Researchers estimate the cells themselves only reproduce once every 10,000 years or so, causing some to question whether the bacteria can even be fairly called 'life'.

Dr. Beth Orcutt, a scientist at the Bigelow Laboratory for Ocean Sciences in Maine (and leader of the very cool Adopt-a-Microbe program), referred to the cells as being in an "almost zombie-like state."

"The other question we have is that even though we are finding cells," she told BBC News, "is it really true to call it alive when it's doubling every thousands of years?"

It's an interesting point. We thought that drop of pitch experiment took a long time. How do you study something that only really 'does something' every few thousand years?

Still, it seems unfair to move the goalposts of what constitutes life just because they aren't doing it fast enough. Given their numbers, these long-lived deep-sea microbes could be the dominant form of life on our planet! It's not so much how concentrated they are (which is actually fairly low compared to their land-dwelling cousins), but the fact that there is a lot more ocean floor than dry land, and — at least so far — there doesn't seems to be a limit to the depth that these cells can be found.

"The deeper we look, the deeper we are still finding cells," Dr. Orcutt told BBC News, "and the discussion now is where is the limit? Is it going to be depth, is it going to be temperatures? Where is the limit from there being life to being no life?"

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It might not be only Earth that counts these kinds of microbes as a dominant form of life.

Finding 'life' like this here at home gives hope to astrobiologists looking for life elsewhere. Speaking to The Society for Science & the Public, SETI astronomer Seth Shostak offered the thought that discoveries like this bolster hopes of finding life on other planets, saying: "Earth is prime real estate, but most things in the universe probably live in subprime."

Popular candidates for life in our solar system include Mars and Saturn's moon, Titan, as well as Jupiter's Europa and Saturn's Enceladus, both of which may be hiding water oceans below their icy outer crust.

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