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Chemical bonds fuel sea life in hydrothermal vents, oxygen comes from stardust

Q: Where does the energy come from that sustains life around the ocean’s hydrothermal vents? (Harry, Newark, Delaware)

The submarine Alvin’s manipulator reaches toward a hydrothermal-vent chimney, seen through the sub’s viewport, at 17 S on the East Pacific Rise. The “black smoke” contains life giving chemicals. [Patrick Hickey, Woods Hole Oceanographic Institution]

A: Chemicals formed deep within Earth provide the energy. Microbes release the energy by breaking chemical bonds to form sugar — life’s fuel.

Chemicals. The seafloor leaks in places. It’s riddled with multitudinous cracks and fissures along the crests of ocean ridges — where plate-tectonic action cracks and spreads apart the seafloor. Gigantic plates that meet at mid ocean move apart. Molten rock wells up into the fissures.

Seawater oozes down through the cracks. A mile or so under the floor, the trickling water reacts with hot rocks and leaches out various metals and minerals — copper, zinc, and iron, for example. The hot chemical-laden brew returns to the surface and spews out cracks and vent chimneys. See figure.

Life. Microbes eat the vent-water chemicals.

Vent life runs on the same fuel we do — sugar. The sugar factory down there, though, runs on different power. Not plants grabbing energy from the Sun but rather microbes releasing energy from chemicals. Different microbes favor different chemicals.

Tubeworm lives off sugar from microbes. It has no mouth and no stomach. [High-definition images copyright Woods Hole Oceanographic Institution and the BBC Natural History Unit, courtesy of the WHOI Advanced Imaging and Visualization Laboratory and Johnson-Sea-Link submersible, Harbor Branch Oceanographic Institution.]

For instance, vent bacteria take hydrogen sulfide from upwelling vent water. They break the chemical bonds of the hydrogen sulfide and, with oxygen and carbon dioxide from seawater, use the bond energy to create life-supporting sugars.

Microbes grow everywhere — on rocks, inside the vent chimney walls, even inside animals where they form symbiotic relationships. The deal: sugar for a safe home. Vent tubeworms don’t even have mouths or stomachs.

Bacteria, using the chemicals, form the "basis of life at vents, but not only as symbiots," says Diane Poehls, Woods Hole Oceanographic Institution biologist.

Most vent animals do have mouths and stomachs. They graze, like cows, on bacterial scum or filter bacteria out of vent water. Predators and scavengers don’t eat bacteria directly but do eat bacterial-fed animals.

Bottom line: Chemicals provide the energy. Microbes break chemical bonds and use the energy to make sugar. That sugar feeds vent life.

Further Reading:

Woods Hole Oceanographic Institution: The caldron beneath the seafloor by Susan Humphris and Thomas McCollom

Woods Hole Oceanographic Institution: Dive and discover — Vent Biology

USGS: This dynamic Earth: the story of plate tectonics by W. Jacquelyne Kious and Robert I. Tilling

Q: Where does oxygen come from? (Shirley, Sequim, Washington)

Nineteen years ago, astronomers spotted the brightest supernova (1987A) seen in 400 years.  The shock wave unleashed during the star’s explosion ripped into a surrounding ring, compressed it, and heated it — blazing hot. 2003 image. [NASA, P. Challis; R. Kirshner, Harvard-Smithsonian Institute for Astrophysics; B. Sugerman, STScI]

Stardust. Stars make oxygen deep inside and a few of the biggest blast it into space as they go supernova. Not only oxygen. Other than hydrogen and helium, almost all elements come from supernovae.

During the main part of a star’s life, it fuses hydrogen nuclei into the next heavier element — helium.

Take our Sun, for example. Every second, the Sun generates energy this way in a highly dense, extremely hot fusion-furnace core. In the furnace, the Sun changes 508 million tons of hydrogen into 504 million tons of helium and converts the "left over" mass (4 million tons) into energy, according to Einstein’s equation, E = mc². It has done this every second for the past 4.5 billion years of its life.

But, the Sun and all stars eventually run out of hydrogen to convert into helium. Then they convert helium into the next heaviest element — carbon. And so on.

At each stage in their life they fight the battle against collapse. Converting elements generates energy, which produces pressure, which holds the star up against the enormous inward pressures of gravity. A star’s mass always threatens to collapse it.

As long as the star is hot enough, it can keep on going — converting one element into the next heavier element. Stars larger than about eight times the Sun’s mass go through the elements, in turn, producing first helium, then carbon, oxygen, silicon . . . Until it hits iron, which doesn’t release energy when a star tries to convert it. Collapse! Not enough outward pressure.

For the big stars (at least 8 times more massive than the Sun), this collapse is catastrophic. The star core collapses in about a second, pushing the nuclei in the central regions together to form a dense tiny neutron star. That’s bad enough, but worse — infalling gas hits the dense rigid core, bounces back, and sends a shock wave outward that blasts off the outer layers. The star literally tears itself apart.

In so doing, it releases a fireball of light — sometimes enough to outshine an entire galaxy for a few days — and casts off oxygen and other elements. From this stardust, new stars and planets are born. Oxygen and all life’s elements come from the stars.

Further Reading:

Royal Observatory Greenwich: Supernova

Cornell University: Ask an Astronomer — supernovae

(Answered Jan. 7, 2004)