Where is Life?


Chris Chyba
Carl Sagan Chair for the Study of Life in the Universe
SETI Institute & Stanford University

As far as we know, life is a planetary phenomenon. That is, life as we know it is going to live on either a planet or a moon, a satellite of another planet.

...it's not out of the question that there could be an ecosystem that lives entirely in the atmosphere of a planet like Jupiter or Saturn, but you know if you look at the Earth, life exists almost everywhere where there's liquid water on the Earth. But there seems to be, as far as we know, there seems to be no entirely airborne form of life.

One of Chris's scientific colleagues puts it this way: why are Earth's clouds not as green as grass, as full of life as rainforests?


Chris Chyba
Carl Sagan Chair for the Study of Life in the Universe
SETI Institute & Stanford University

...it seems like there are limitations probably on how long you can stay suspended in the atmosphere. In any case it looks as though atmospheres are bad places to find life. So probably worlds like Jupiter and Saturn don't have life on them.

A canal or giant city on another planet would be a sure sign of life.

Or if that face were real, we'd know for sure.

But in the absence of that kind of sign, we have to look for what nealson calls "bio-signatures"-other signs of life.


Ken Nealson
Director, Center for Life Detection
Jet Propulsion Laboratory, NASA/Caltech

Most of you have seen bio-signatures like this. Uh, they're called fossils. This particular one is from the Green River formation in Wyoming ...and you can see there is no question that this is a bio-signature. This is proof of former life on this planet. If we found a rock like this on Mars or anywhere we would be overjoyed. But what about the other side of the rock? Believe it or not, this is a bio-signature too. But in this case, we need to look at in at very high resolution and see the bacterial bodies and other things that might be preserved in a rock like this.

So, as you get to more primitive life which is what life was like on Earth for the first 2 and a half billion years, the bio-signatures become less and less obvious and the challenge becomes more and more.

We don't imagine that every planet or move would have advanced and structural intelligent life and you don't want to miss it if it looked like Earth did 2 billion years ago. What we want to do is develop "bio-signatures" that would never miss life no matter what the form that its in.

Sometimes what seems to be a bio-signature may be, at best, ambiguous.

Take the famous Martian meteorite, ALH 84001.

It was found by an NSF-NASA research team like this one, out on the blue ice fields of Antarctica.

Then researchers at NASA's Johnson Space Center shocked the world with an announcement that they believed these squiggly shapes were likely Martian microbes, fossil relics of a time when Mars was more hospitable than today.

Others said these forms were just too small for any kind of life, and questioned whether some of the apparent signs of life entered the rock after it fell onto the Antarctic ice...

On all these matters, the scientific jury is still out...

Skeptics used to say that looking for life beyond Earth was a science without a subject.

But in the past 2 decades discoveries down here on Earth have proved that life as we thought we knew it was not the only kind of life there is, even here on our own planet.


Ken Nealson
Director, Center for Life Detection
Jet Propulsion Laboratory, NASA/Caltech

I'm a micro-biologist by training and my field has changed almost 180 degrees, almost completely turned upside down in the last 20 years. Uh, because of the discovery of what we might call extreme environments and the organisms that live there. I have an example of one of those extreme environments here.

This is a rock from the bottom of the Pacific, from the hydro-thermal vents. The water coming out that forms these rock formations is on the order of 300 degrees centigrade... and can remain liquid because of the high pressures at the bottom of the ocean.

As it comes out and starts to cool down, it's full of chemicals that allow microbes to live in this environment, even when it's hotter than boiling.

Uh, these are called extremophiles. And the discovery of such extremophiles that could live at a hundred centigrade or higher, completely changed the way we viewed life on this earth and spurred a lot of research into other extremophiles.

We've found life not just in extreme heat, but also in extreme cold.

Earth's South Pole is nearly 2 miles high in elevation and surrounded by hundreds of miles of empty ice.

Just a few years ago, the textbooks said that apart from humans with our powerful technology, nothing could live here.

But then in 1999, researchers discovered these microbes happily living in the ice, taking in energy, reproducing and doing all those things which plants or penguins do in more clement places, and which are characteristic of life.

Hot... cold... what about deep down below earth's surface?


Chris Chyba
Carl Sagan Chair for the Study of Life in the Universe
SETI Institute & Stanford University

What we have learned about life on Earth in the last decade or so is that life doesn't only live at the surface. There is a so-called deep biosphere on the earth. Life can live miles underground. And in fact it looks as though there is as much life underground in terms of total mass of living things as there is in all the life on the surface, and that includes, in fact that's dominated by trees. Trees make up well over 90 percent of all the biomass on the life of the earth. So it's kind of a staggering picture if you think about life living underground, which is exclusively microbes once you get below the upper few feet. There's nothing but microbial life underground. And yet all those single-celled organisms add up to as much mass as is present in all the forests on the surface of the earth.

If it is the case as it apparently is from the Earth that life can exist in a deep biosphere, then you have to ask, could there be worlds where there is no liquid water at the surface but would still harbor life because that life is living underground?

And... probably... the answer to that question is yes.


Ken Nealson
Director, Center for Life Detection
Jet Propulsion Laboratory, NASA/Caltech

What we've discovered is that virtually any environment that allows liquid water to be there, will be compatible with life... that life has a way of inhabiting every place that has liquid water on this planet.

What we've learned from these extreme survivors here on earth opens our minds to new possibilities as we look for life in other places in our solar system.