Organisms using thermal energy as their sole energy source

Question

After seeing this question I remembered that in secondary school we watched a documentary stating something along the lines of "all organisms derive their energy directly or indirectly from the sun. *pause* Well, except a couple of organisms in the deep sea cultures that get their energy from small undersea volcanoes" . Now, after doing a lot of searching I was able to find the 'giant tube worm', however that still indirectly relies on energy from the sun as well as it relies on free Oxygen being available that in the end comes from photosynthesis (if my understanding is correct). So my question is two fold, am I correct in my understanding of the giant tube worm and if so, are there any organisms that function in a way that does not require any energy source beyond geothermal energy?

Answer 1

I had to re-read your last sentence a few times to make sure I understood it correctly, but I think that now I do, and I can answer your question.

What you're talking about are thermophiles. They're small organisms that love hot conditions - up to nearly 250 degrees Fahrenheit. They can be found places with a lot of hot water, such as hot springs - and, yes, ocean vents. Many use sulfur as a fuel during chemosynthesis, oxidizing it to make sulfuric acid. They take the energy from the heat source to do this.

Not all thermophiles use chemosynthesis. Those in hot springs may get a lot of sunlight, and they can use photosynthesis. However, those in the deep sea cannot undergo photosynthesis, and are forced to use the energy from the vents to undergo chemosynthesis. In fact, entire ecosystems can be built off them!

Thermophiles may even have been some of the first organisms on Earth. Around the time that life is thought to have first formed, Earth wasn't a very hospitable place. As Ashwini Kumar Lal writes of the first forms of life,

Many of them are evolutionary relics called “archaea”, believed to be among the first homesteaders on the Earth 3.8 billion years ago. They are presumably the first version of life on our planet when its atmosphere was devoid of oxygen, and comprised largely of ammonia, methane, water vapour and carbon dioxide. They are microorganisms similar to bacteria in size and simplicity of structure, but continue as an ancient group intermediate between bacteria and eukaryotes. Heat – loving microbes, or “thermophiles”, are among the best studied of the extremophiles that can reproduce or grow readily in temperatures exceeding 45º C, and some of them, referred to as “hyperthermophiles”, are capable of thriving even thrive in temperatures as high as 110º C – more than boiling water temperature.

While we do not know (and may never know) the truth of this hypothesis, it is certainly plausible, given the locations where some extremophiles have been found.

---

References:

1: Microbial Life in Extremely Hot Environments

2: http://en.academic.ru/dic.nsf/enwiki/18641 (link no longer works, for some reason)

3: Origin of Life

Note: While I list several Wikipedia articles throughout the answer, I did not use them for the information in this answer. I think they're a good starting point to lead you to other sources, though.

Answer 2

Organisms do not survive solely on heat. The organisms you mention that are (more or less) independent of the sun obtain their energy by oxidizing inorganic compounds, like iron or sulfur. For example, some bacteria oxidize ferrous iron (Fe$^{+2}$) to ferric iron (Fe$^{+3}$), which releases some energy that can be used to "power" the cell. A list of various reactions used by these bacteria is found in this Wikipedia article.

The reason these species exist at hot thermal vents is not because the heat is helpful as such, but because iron, sulfur and other energy-rich inorganic materials are released into the ocean at these sites. The bacteria have adapted to tolerate the heat so that they can harvest the inorganic materials; but they don't benefit from the heat in itself.