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How do creatures survive without the sun? Add to ...

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.

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