Does all life depend on other life?

A question raised by my wife, but one I’m interested in as well: Do all living things (on Earth, of course) depend on other living things, or the remains of previously living things, to grow and reproduce? Are there any organisms that can survive and prosper with, say, just sun and water, without the need to consume nutrients from other living or formerly living things?

You can get rootless plants. So, yes, with the right biochemistry all you need is light, air, and water.

Sun and water? No. Chemicals oozing from volcanic vents in the deep ocean floor? Maybe, in theory. Google chemoautotrophs.

In theory, organisms like cyanobacteria could under the right circumstances obtain necessary dissolved inorganic nutrients from water, and use these together with sunlight and atmospheric carbon dioxide to make food. However, in practice nutrients derived from the decay of or excreted by other organisms are so prevalent that most organisms will be using these.

Right, although the same caveat applies that organisms may be absorbing some nutrients from the decay of other organisms.

“Air plants” still require nutrients, which they acquire from dust particles in the air or rainwater. Again, at least some of these were previously contained in living organisms.

Thanks, Colibri et al., I was kind of thinking along those lines, that life-derived organic compounds are so prevalent now that it would a rare form of life that didn’t take advantage of that. So, two followup questions:
[li]Are we reasonably certain that there are no current life forms that live on only inorganic nutrients? Do we know enough about the primary producer organisms living in/near the deep-sea vents to say one way or another about them?[/li][li]What do we know about ancient organisms? Presumably, the first life forms had to rely on only what compounds existed before the advent of life (if we can even draw a line there somewhere), but do we know anything beyond such speculation?[/li][/ul]

Some higher end photosynthetic bacteria have the ability to make everything they need, if given sunlight, some inorganic minerals, and water. The bacteria have these clever control mechanics where they don’t produce things that are in abundance in the environment, but some of them still have the genes to make just anything.

So no, that kind of bacteria doesn’t depend on anything else but a nonbiological environment. I’ve grown some in college.

For keeping humans alive, for evolutionary reasons that are too complex to explain easily (has to do with generation number and genetic drift), we need a larger array of biologicals to keep us kicking. But it’s not as broad an array of species as you think. Probably a few dozen strains of photosynthetic algae and bacteria could be used to make a closed loop life support system that could keep human beings alive indefinitely.

It should be noted that nitrogen, a key chemical element in all forms of life as we know it, is fixed from atmopheric sources by diazotrophs (bacteria and archea) using the enzyme nitrogenase. Although some plants and a few animals have formed symbiotic relationships with diazotrophs to perform nitrogen-fixing internally, all life is dependant upon these organisms for a bioavailable source of nitrogen. We currently synthesize a significant amount of ammonia from natural gas to support our intensive agriculture because of the lack of readily accessible and safe sources of natural bioavailale sources of nitrogeneous compounds.


While biological fixation is far and away the most important process, lightning can also produce nitrogen oxides from atmospheric nitrogen, which are brought to the ground by rainwater as nitrates. These make up about 5-8% of the total nitrogen fixed. So some nitrogen would be available even in the absence of diazotrophs.

Not to mention that our current atmosphere itself is the waste products of organisms. And in my earlier response, I neglected that the oceans are essentially dinosaur pee.

But wouldn’t the atmospheric carbon dioxide eventually run out? Don’t they require animal respiration to keep a steady supply?

Could a planet with no life but cyanobacteria sustain itself for long?

I was thinking about that, too, but fires would eventually restore the balance.

What would burn? No trees, remember.

Photosynthetic organisms still use oxygen - when there is no sunlight, such as at night, plants use oxygen to keep their metabolism going.

Probably, but most likely because something would mutate sooner or later to eat the cyanobaceria setting up an actual ecology more like what we’re used to seeing.

Remember, life was at the level of pond scum on Earth for a couple billion years before developing new fangeled things like multicellularity.

I think the big thing was the development of eukaryotic cells. It seems that multicelluarity was an easy change after that. Of course you could argue that that development was just a kind of endo-multicelluarity. But life was prokaryotic for a couple billion years.

I have wondered whether anything was happening during that 2 billion years that prepared the way for eukaryosis or did it just take that long to happen at random. If the latter, it might have happened instantly or might never have happened, not before the sun went red giant and swallowed the earth.

Recently re-read a book called Oxygen: The Molecule That Made the World that attempts to discuss that.

For much of Earth’s history there wasn’t much oxygen in the atmosphere, and for most life of the time it was poisonous (technically, it still is poisonous, even to us who depend on it, but our bodies have learned to cope with current levels. Significantly higher levels can cause all sorts of mayhem.) Some cells learned to utilize sunlight and carbon dioxide to generate chemical energy, but produced oxygen as a waste product. Chloroplasts are the descendants of those cells which took up residence in other cells. Some other cells learned to utilize this waste product to produce chemical energy, and those cells took up residence in other cells and became mitochondria. But mitochondria aren’t terribly useful unless there’s a certain level of oxygen. There’s also complications about carbon sequestration leading to “excess” oxygen boosting levels, ice ages, and various other things that require long time spans.

Eukaryotic cells were probably around for a long time before true multicellular life got started because there’s a certain threshold level of oxygen needed before it becomes a viable lifestyle. (Multicellular is distinct from clumps of cells living in close proximity, like stromatalites. By "multicellular I mean organisms were the cells are interdependent on each other rather than just accidental neighbors)

There were probably all sorts of interesting evolutionary things happening in cells for all those billions of years - new means of extracting energy from surroundings, new chemical defenses, new chemical attacks, all sorts of stuff - that we don’t know about because fossils don’t give us that information. But there are indications that lots of stuff was going on - iron pyrites generated from sulfur using bacteria, for instance. Fool’s gold is bacterial poo, in that sense. Banded iron formations may have been caused by life, massive, massive sediments of iron ore that stole oxygen from the air during their formation, keeping atmospheric oxygen levels low until the dissolved iron in the oceans “rusted” out. Then there were the natural nuclear fission areas in Gabon, where uranium oxides accumulated and underwent fission before being buried in more sediments.

So there was a lot going on for 4 billion years prior to the Cambrian Explosion of multicellular life. Among other details, there are current estimates that the eukaryotes date back 2 billion years… meaning for 3/4 of their history eukaryotes were single cells. It’s the multicellular thing that suddenly took off half a billion years ago and gave us the world we have now. That may be the thing with low odds of happening.

Volcanoes also produce carbon dioxide. It is a relatively small amount compared to other fluxes but CO2 would still be present in the atmosphere in the absence of life. As noted, photosynthetic organisms also respire, so that CO2 is recycled.