Ten weeks to impress your Dinner Mates: Week 7 : Let's impress people with Life !

Does Life depend on the Sun ?

Food chain

As you all know, food chain is the link between all species in an ecosystem by considering the predator-prey relationship. "What are the preys of this creature ?" is the key question and if you repeat the question on each prey it will lead you to autotroph species, in other words plants and phytoplankton.

Indeed those organisms don't hunt, they have no prey because they create their own food. That is why they are the first level of the food chain.

Photosynthesis use chloroplasts inside the cells

How do they create their food ? Again, you know it. Thanks to the famous chemical reaction called photosynthesis.

As you can see this reaction involves light provided by sun. So it is easy to concluded that without sun there is no photosynthesis, so, there is no plants and phytoplankton which are the first level of food chain, and so, no life on earth.

Deep sea creatures

What about those monsters that live in the depth, never see the sunlight, hunt in an ecosystem with no phytoplankton and can produce their own light ?

Angler fish (it use a luminous lure to attract its preys)

Another angler fish (even more cute don't you think ?)

It seems that they escape from our conclusion. Well, not really. Actually they depend on the food from above, the food chain in the depth is based on scavengers which eat corpses that drift down from the water surface and so, without sun they couldn't be able to feed themselves.

Hagfish (As you can notice it has no eyes, this is because it lives in total darkness)

Hagfish (beautiful teeth but no jaws)

Hagfishes are scavengers (here they are eating a whales corpse)

Black smokers and cold seeps

Well, even in the darkest area, the sun seems to be the key to provide life, so the answer to the question " Does life depend on the sun ? " should be "Yes" . Not so fast !

Giant tube worms

In 1977 scientists discovered ecosystem around hydrothermal vents. That was an incredible surprise because the conditions are extreme, 80°C, very salty water, hight pressure (100 to 500 times stronger pressure).

Black smoker surrounded by tube worms

The food chain there is based on chemosynthetic bacteria that can produce organic material from hydrogen sulfide thanks to chemosynthesis

6CO2 + 6H2O + 3H2S = C6H12O6 + 3H2SO4

In 1990 another sun-independent ecosystem has been discovered, called the cold seeps.

Underwater lake

It also relies on chemosynthesis but this time not mainly from hydrogen sulfide but methane.

Personal commentaries

So the answer to the question "Does life depend on the sun ?" is "No", there is life, in black smokers and cold seeps, that can live without sun but it is a highly rare phenomenon and anywhere else the answer would be yes, and even in those ecosystems a total independence is uncommon because most of the creatures needs oxygen which is provided, again, by photosynthesis and so depends on sun.

The most exciting thing about that is maybe that discovery and exploration is still possible, scientists discovered those places only 34 years ago and less than 1% of the surface of depth area has been explored. In other words our childhood dreams of adventure in unexplored and wild realm is "feasible". Moreover you also will have to face monsters such as giant squids or angler fishes. Isn't it like a real epic adventure novel ?

"Twenty Thousand Leagues Under the Sea" novel by Jules Vernes

Giant squid illustration

What about the underwater lakes ? Isn't it wonderful ? To us it is a fantasy story becoming real.
One of our most beautiful dream would be to be offered a journey into a submersible, 5 000 meters deep.