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How do creatures survive without the sun?
wonderquest
April Holladay

This article was published more than 14 years ago. Some information may no longer be current.

How do animals or insects that live deep under water or far in the Earth get vitamins and energy from the sun? Do not all living things need the sun to live? Jean-Pierre, Windsor, Canada

Where does the energy to sustain life around sea vents come from? I have heard that sulphur plays an interesting role. Harry, Newark, Delaware, USA

Your questions lead us along life's most basic path - survival of the species- the primary function of all organisms. When a creature successfully manages to reproduce, it has done its job. The task, though, can be difficult, especially along the fringes of the web of life - in the deep dark.

Almost all life on Earth is part of a web that gets its energy ultimately from the Sun. Each life form in the web usually exchanges nutrients with other life forms. But, if the environment can supply basic needs, strange singular forms can exist independently of all other life and even of the Sun.

All cells must have three things to survive:

  • Energy to run the activities of their cells (such as, combining nutrients to make sugar and thereby release energy).
  • Liquid water to dissolve chemicals and allow them to mix together and react. "Liquid" because liquid water is the right temperature for essential chemical reactions to occur in cells.
  • Chemical building blocks.
  • ----- Carbon for its ability to form long chain-like molecules (like sugars and proteins). Every living thing on Earth is made from a set of molecules built around carbon atoms.
  • ----- Hydrogen and oxygen to bond with carbon and also make water. By the way, of the approximately twenty-four atoms required, 95 per cent of the human body is made up of just four atoms (carbon, hydrogen, oxygen and nitrogen)
  • ----- Nitrogen likewise to bond with carbon and also to bond with hydrogen and oxygen and form stable, large molecules.
  • ----- Other elements: sulphur, phosphorus, sodium, potassium, magnesium, calcium, manganese, iron, cobalt, copper and zinc.

Carbon is the key. "The concentration of carbon in living matter (18 per cent) is almost 100 times greater than its concentration in the Earth (0.19 per cent). So living things extract carbon from their nonliving environment," says biologist John W. Kimball , author of Biology. Given energy, though, organisms can do the extraction work.

How cells manage to survive without the Sun

You ask specifically about those animals that live in the deep dark of rock or sea. These creatures, over millions of years, evolved to use energy supplied from our planet rather than our sun.

Such organisms use inorganic chemicals (usually hydrogen and hydrogen sulfide obtained from rocks and sea water) for energy instead of organic matter. They utilize carbon dioxide as their carbon source.

Geothermal, rather than solar, energy catalyzes chemical reactions that create life-sustaining inorganic molecules. Organisms consume the inorganic chemicals and convert them to life's fuel ¯ usually sugar. Water is the only absolutely essential ingredient deep organisms need in addition to the inorganic chemicals they mine from their surroundings.

Let's investigate two species to see how they get energy ¯ without direct sunlight ¯ one living in deep rock (deeper than we have found any other creature) and a distant cousin living in the deep sea.

Deep rock life

The microscopic (4-micron) creature lies within a cage of surrounding hard, dense volcanic rock (basalt) in a dark, sulfur-stinking pool of scalding-hot salty ancient water. Millions of tons of rock press in all directions upon its tiny body 2.8 kilometers below ground and raise the temperature of its home to 60 degrees Celsius (140 F). No whiff of air, no glimmer of sunlight ever penetrates this far beneath Earth's surface. Its species name is D. audaxviator ¯ bold traveler. I call the organism "Dax."

This type of heat-loving bacterium (called a thermophile ) has lived between 3 to 25 million years ¯ totally cut off from surface life, imprisoned in 3-billion year old basaltic rock.

You ask how it manages. The D. audaxviator species is doubly unusual. It not only does not need the Sun but also does not need any other life. Most bacteria sponge off other species for some needs ¯ for example, bacteria around sea vents rely on planktonon the sea surface to produce oxygen from photosynthesis. Then sea-vent bacteria merely take oxygen from deep seawater put there by the surface-dwelling plankton.

But Dax is unique in that it survives alone in deep rock. Dax must extract all its needs from its sterile surrounds and then, by itself, manufacture organic molecules out of water, inorganic carbon and nitrogen (from ammonia) it gets from surrounding rocks and fluid.

Decaying uranium indirectly fuels Dax' energy needs. As uranium decays into lighter elements, it releases energy. The freed energy catalyzes chemical reactions that produce hydrogen and sulfate ¯ Dax chow. Dax releases the liberated energy in a series of careful steps to power cell work . For instance, it combines hydrogen and sulfate to produce lower-energy hydrogen sulfide, which Dax exports into the environment ¯ Dax poop.

By the way, if Dax were to release its energy in a single step, the energy stored in molecular bonds would escape in the form of heat, bursting Dax into flames. So Dax proceeds with its potentially hazardous task gingerly, in many small controlled reactions.

Revving up its one-cell factory, Dax makes cellular building blocks: amino acids for proteins, genetically-coded chains of DNA and RNA for reproduction and lipid fats for cell membranes.

However, Dax' food supply is too meager for much more than survival in this perhaps harshest of Earth's living spaces. Furthermore, oxygen kills the organism, which implies it may have been separated from Earth's surface for millions of years.

"What's remarkable is that Dax, on its own, carries out the cellular functions that entire communities of bacteria are required to do in other environments, says geoscientist Tullis C. Onstott of Princeton University.

Indeed, "The fact that the community contains only one species stands one of the basic tenets of microbial ecology on its head," says astrobiologist Carl Pilcher of NASA.

In 2006, geoscientist Tullis Onstott, Lisa Pratt of Indiana University and their team from nine collaborating institutions discovered Daxand his fellow species bacteria living totally alone ¯ isolated from all other bacteria cultures ¯ deep within South Africa's deepest goldmine. The water that sustains the bacteria was undiluted by surface water and between three and 25 million years old. D. audaxviator is a distant ancestor of many thermophiles.

In 2008, Dylan Chivian of the Lawrence Berkeley National Laboratory, California analyzed and sequenced Dax' genome. The genetic structure revealed by Chivian's analysis informs us of Dax's potential abilities.

Deep sea life

Modern relatives of D. audaxviator living in hydrothermal vents (geysers on the seafloor) get their primary energy from chemical bonds. Heat from molten rock far below the seafloor raises trickle-down seawater temperatures to well above 350 degrees C (660 F). The hot seawater reacts with ocean-crust rocks causing the hot water to pick up hydrogen sulfide, which then up-wells with the vent water.

"Vent bacteria (Dax' cousins) break the chemical bonds of the up-gushing hydrogen sulfide and use the bond energy to combine oxygen (or nitrate) with carbon dioxide (which comes from seawater) into stable, biologically useable compounds, such as glucose", says marine bioscientist Barbara J. Campbell of the University of Delaware.Dax' cousins make sugars within their one-cell bodies and use energy from the sugars to power cell life.

Other vent organisms that can't synthesize their own food gobble these compounds. Sometimes vent organisms also eat the vent bacteria or their waste products. Dax' cousins thus contribute nutrients to the vent community and form the base of the food web.

These thermophiles never see the Sun or encounter a breath of oxygen, but survive 2.4 kilometers (1.5 mi) below the sea surface.

Life's start (and waning years)

We may never know how life started, but I wonder if life retreated to a safe refuge in the deep sea or below Earth's crust when huge meteorites crashed into our planet. Certainly the environment was less hellish below. How about Mars? Maybe her surface is lifeless now, but her deep rocks, like ours, may harbor abundant life.

"With the discovery of an organism capable of living in complete isolation from the photosphere, we can begin in earnest to search for subsurface life on planets like Mars," says geoscientist Lisa Pratt of Indiana University.

In 1992, astronomer Thomas Gold of Cornell University speculated that the mass of all subterranean microbes equals the mass of all organisms on or above Earth's surface.

Further Reading:

April Holladay lives in Albuquerque, New Mexico. Her column, WonderQuest, appears every second Monday of the month on globetechnology.com. To read April's past columns, please visit her website . If you have a question for April, visit this information page .You can also comment on this article at Google Groups

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