Q: Have life forms been discovered in these undersea volcanoes?
Kelley: Yes. In 1991 they dove on this very active hydrothermal area right after a volcanic eruption, and saw this cloud of material coming from the holes and fissures in the sea floor. It looked like a snowstorm, like seeing snowdrifts on the ocean floor.
Then, in 1993, almost immediately after the Navy let NOAA have access to the data from the SOSA system’s hydrophone array, there was an eruption. And a ship out there at the time was able to trace the eruption in the water column.
So three months later we went out and dove on it. And we saw all of this microbial material coming out of the ocean floor where this eruption had occurred. So these two events — in 1991 and 1993 — documented a very large microbial community living in the sea floor to some depth. And there have since been about eleven documented eruptions causing this effusion of microbial material, in places where there was no evidence of this kind of venting beforehand.
And also in 1993, when we sampled the water in the area of the vents formed by the eruption, we found that the microbes coming out of the fluids grew optimally at temperatures much higher than the temperature of the venting fluids.
Q: So they lived better at temperatures higher than the temperatures at the vents?
Kelley: Right. They like to grow at say 90 degrees Celsius (about 200 degrees Fahrenheit), but the vent fluid temperature was around 40 degrees Celsius or lower. These organisms can’t grow at lower temperatures, so the idea is that somewhere beneath the sea floor there’s a much warmer environment.
Q: Is that where you think these microbes live?
Q: Below the sea floor?
Kelley: At some depth below the sea floor there is, very probably, a substantial microbial community. We don’t know how far away from the spreading centers yet.
Q: About how deep do you think this microbial community extends?
Kelley: We aren’t really sure. As long as there are nutrients down there, volcanic gasses, there’s no reason they can’t live.
Q: What are their sources of nutrients?
Kelley: The nutrients are in the water column and vent fluids. There’s no sunlight down there. So these microbes have to obtain their energy from something else. So they utilize things like carbon dioxide, methane, and hydrogen, all of which are expelled during volatile eruptions. The large microbial blooms are believed to be caused because the eruptions cause a very large increase in these nutrient-rich gasses.
Some of the microbes we’re most interested in have very high tolerances for toxic metals — things like cadmium, arsenic, mercury. Anything that, you know, would (laughing) normally kill us off quite easily, these guys can utilize as an energy source. They are just incredibly adaptive little critters. Whatever’s there, they somehow can rearrange to use.
Q: And they live in the water, but beneath the sea floor?
Kelley: The sea floor contains lots of cracks and pores and fractures. And the idea is that they live in these water-filled pore spaces, and attach themselves onto the rocks. And then as fluids circulate by they just use what they need.
Q: What exactly is a microbe?
Kelley: A microbe is a single-celled organism. Very primitive. Has a single molecule of DNA. A lot of people would now say a specific kind of these organisms — called Achaea — may represent the most ancient of organisms on Earth. There’s a lot of interest in them because of that, and also because they’re just incredible little animals. We know they live at temperatures up to 113 degrees Celsius, and there’s good evidence now to suggest that they live at even higher temperatures.
Q: That’s above the boiling point.
Kelley: But, you know, most areas we look at are under almost 6,000 feet of water, so the boiling point is higher than what you would see on the surface. In the submarine environments the actual boiling point is 407 degrees Celsius.
Kelley: They are boiling, though. There are lots of places on the sea floor where there’s actually a vapor phase generated.
Q: So these microbial organisms are living in boiling water at the bottom of the ocean?
Kelley: No, they are carried in the high-temperature water. We do not yet know what the upper temperature of life is.
Q: And some of the organisms around these vents may represent the most ancient organisms on Earth?
Kelley: There is some thought of that. Organisms, plants, and animals can be differentiated by their genetic make-up. One of the ways to visualize how similar or dissimilar organisms are is to describe the genetic make-up on a “tree of life.” And when you look at the genetic structure of the high-temperature organisms in the vents, it looks as if they are very close to the bottom branch of the tree. Because of this and for many other reasons, many people think that it is in the vents were where life may have originated.
Q: What are some of the other reasons?
Kelley: Another reason is that all the nutrients that you need — that the microbes need — are there. And as soon as there were oceans on Earth, over four billion years ago, there were hydrothermal vents on the sea floor.
Also, early in Earth’s history there was a long period of bombardment by meteorites, lots of impact events. And people now think a lot of the major extinctions were created by these big impacts. And these massive impacts vaporize — wipe out — a lot of the continental environments. But unless you vaporize the whole ocean, it’s a very safe habitat. It’s hard to disrupt ocean temperatures. So these organisms could have survived these massive impact events.
Q: Does this theory compete with the idea that microbes arrived from other planets through asteroids and meteors?
Kelley: (Laughing) I think “compete” is probably, um…. It’s hard to tell what stuff comes through the atmosphere and survives. There are a couple different theories. My bias is that you don’t need it, right? Everything that the organisms need to live is already there, so you don’t require any outside source of material to explain the origin of life on Earth.
Q: It seems more plausible
Kelley: I’m more comfortable with it.
Q: How would the story go from the point at which the microbes are coming out of the vents to where life gets up to the surface of the planet?
Kelley: It’s unclear how they evolve over time, but certainly there’s reason to believe the cell structure becomes more complex. I’m not a biologist, I look at rocks. But you know, it would be a general textbook version of how things get more complex and eventually you get fish. So it’s kind of the standard evolution model.
Q: Do you think there might be something like these organisms that live in these undersea thermal on other planets?
Kelley: I think probably one of the most important things that we recognized was the connection between volcanoes, fluids, and life. And if you have warmth, and volcanoes, there’s probably no reason you can’t have life. And so NASA is very interested in learning about these systems. It’s estimated that we only know about 1% of the kind of microbial life that lives in submarine environments.
Kelley: Yes, and yet there’s good reason to believe that if you took all that biological material on the ocean floor, and put it in a heap, it’s more than what exists on the continents. And yet we hardly know anything about it. But NASA’s very interested in using the vents as a test bed, with the idea that if we can figure out how to look for microbial life on our own planet, then we’ll have a much better idea of how to go to another planet and look.
Q: How to look at vents on other planets to see if they contain life?
Kelley: Right. So there’s a lot of interest now in a satellite off Jupiter called Europa, which is really an ice-covered planet. And there’s good evidence that Europa has a liquid ocean. It’s unclear how thick its ice surface is — it may be ten to one hundred kilometers thick — but there’s probably a hundred-kilometer thick ocean beneath that ice. And Europa’s nearest neighbor, Io, is the most volcanically active planet in the solar system. So if there’s liquid water on Europa — which it looks like there is — there’s probably some kind of heat to keep it liquid. So maybe there’s life there. It’s hard to know, but a lot of people believe that if there’s a place that we’re going to go look and find life, then Europa probably offers the best chance.
Q: Can you connect these undersea microbes to the origin of life in the Universe?
Kelley: No! (laughs) I have no idea. I don’t want to go there. I don’t know. It’s magic.