Chemical bonds fuel sea life in
hydrothermal vents, oxygen comes from stardust
Where does the energy come from that sustains life around the oceanís
hydrothermal vents? (Harry, Newark, Delaware)
The submarine Alvinís manipulator reaches toward a
hydrothermal-vent chimney, seen through the subís viewport, at 17 S on the East
Pacific Rise. The ďblack smokeĒ 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 ó lifeís
Chemicals. The seafloor leaks in places. Itís riddled
with multitudinous cracks and fissures along the crests of ocean ridges ó 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
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 ó copper, zinc, and iron, for example. The hot chemical-laden brew
returns to the surface and spews out cracks and vent chimneys. See figure.
Microbes eat the vent-water chemicals.
Vent life runs on the same fuel we do ó 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
Microbes grow everywhere ó on rocks, inside the vent chimney
walls, even inside animals where they form symbiotic relationships. The deal:
sugar for a safe home. Vent tubeworms donít 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
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 donít 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
Hole Oceanographic Institution: The caldron beneath the seafloor by Susan
Humphris and Thomas McCollom
Woods Hole Oceanographic Institution: Dive and discover ó Vent Biology
USGS: This dynamic Earth: the story of plate tectonics by W. Jacquelyne Kious
and Robert I. Tilling
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
starís explosion ripped into a surrounding ring, compressed it, and heated it ó
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 starís life, it fuses hydrogen
nuclei into the next heavier element ó 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 Einsteinís equation, E = mc≤. 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 ó
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 starís
mass always threatens to collapse it.
As long as the star is hot enough, it can keep on going ó
converting one element into the next heavier element. Stars larger than about
eight times the Sunís mass go through the elements, in turn, producing first
helium, then carbon, oxygen, silicon . . . Until it hits iron, which doesnít
release energy when a star tries to convert it. Collapse! Not enough outward
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. Thatís bad enough, but worse ó 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 ó sometimes
enough to outshine an entire galaxy for a few days ó and casts off oxygen and
other elements. From this stardust, new stars and planets are born. Oxygen and
all lifeís elements come from the stars.
Royal Observatory Greenwich: Supernova
Cornell University: Ask an Astronomer ó supernovae
(Answered Jan. 7, 2004)