Deep beneath earth's surface, clues to life's origins | Hacker News Reader

Deep beneath earth's surface, clues to life's origins

quantamagazine.org

81 pointsrbanffy28 comments

Very cool research. On the topic of hydrogen deep underground: I'm not an expert, just a fascinated amateur, but I've been fascinated by the recent discovery that there is enormous amounts of hydrogen below the earth. In fact, this article mentions hydrogen forming by serpentinization, and says that the researchers were shocked to find so much hydrogen. Recent research indicates that hydrogen may exist deep in the earth from processes other than serpentinization as well. There are now a handful of companies working to extract this natural hydrogen to use as a source of green energy. Exciting stuff.

This is an excellent research overview on the topic of "natural" geologic hydrogen https://www.sciencedirect.com/science/article/abs/pii/S00128...

I've also compiled some of my own notes on that paper here which provide some summaries on the multiple fascinating sub-topics. (E.G. hydrogen may be a driver of earthquakes! And we may be able to use hydrogen samples to predict earthquakes! Some predict that there may be even more biomass under the earth driven by sources like hydrogen and methane than there is above ground!) https://docs.google.com/document/d/1pnW4HRq6E2up0DhIoxjCyGS6...

If the Earth didn't have a huge internal geological reserve of hydrogen (and other gaseous chemicals) we'd effectively be a dead planet. It's easy to lose hydrogen to space, which is one reason we don't see much of it in the atmosphere. When we start talking about geologic timescales it would lead to the disassociation and lose of almost all atmospheric gasses. Luckily we have the tectonic plate cycle that puts new gasses in the atmosphere and kicks our eventual extinction down the road a bit farther. This also leads to earth shrinking over these very long time periods.

Let’s hope we don’t find and extract so much subterranean hydrogen that we burn it into water and cause sea level rise.

Don’t forget that oxygen is useful for breathing too. Semi-important, I hear.

ChatGPT estimates that if we converted all of earth’s atmospheric oxygen into water (via burning with hydrogen), ocean levels would rise about 3.7 meters: https://chat.openai.com/share/c9c8ce51-6070-49b6-a092-86e4a4...

I don’t have time to check this math, so take it with a substantial grain of salt.

It will probably increase the concentration of water vapor in the atmosphere, which will lead to further warming as water vapor absorbs the heat radiated by Earth.

This is something I wondered about the idea of life beginning in the oceans and spreading to dry land.

If approximately 70 percent of the total number of microbes on the planet live underground today (number I googled) wouldn't it make more sense that life began underground and slowly spread to the surface? Is this a theory anywhere?

I favor the idea that a planet with a moon in a slightly eccentric orbit (earth) you have oceans washing minerals over every grain of sand on every beach, depositing then washing away different concentrations of everything, wetting and drying and applying sunlight and shade, warming and cooling. A billion billion petri dishes over a billion years. Eventually bingo! organic molecules then life.

I don’t even think it’s the eccentricity that does it, all it matters is that the earth isn’t tidally locked with the moon, that’s what gives you the tides: Earth is rotating faster than the moon orbits and so different parts of the earth face the moon within a day. It also helps that the moon is a significant fraction of the mass of the earth, which means its gravitational influence is significant to the oceans.

Eccentricities also contribute to long duration cycles of tides. Instead of all the Petri dishes following a single cycle, there is also another dimension of longer cycle dishes.

over a billion years

The crazy thing is... it was maybe half that maybe even less. The earth is ~4.5 billion years old. There is perhaps-evidence of microbial life could be ~4.1 billion years old. More certainly, at ~3.7 billion.

The earth is life and life is earth.

It's an interesting suggestion but I think given what we know of life it's unlikely. I guess (obviously this is all speculation - none of us were there!) the origin of life can sort of be thought of as going from chemistry/geochemistry to biochemistry. And purely from a rate of reactions perspective, in a nice solvent like water that's likely to be more conducive to the origin of life than deep underground (in solids/highly viscous liquid at best).

Then there's also flux - do you have temporal/spatial variation in your various chemical constituents that might give rise to potential gradients (as we find in life - chemiosmosis in mitochondria for an obvious example). These are very prevalent at the sort of Lost City hydrothermal vents, where you have a very nice solvent coming into contact with a large mineral flux, with large energetic and chemical gradients. Again, less likely to be found underground.

If you're interested in this kind of thing I'd heartily recommend Nick Lane's book 'The Vital Question' or 'Transformer'. He tends to frame the issue not so much as just having the chemicals available (we find these on asteroids/meteorites!) but in having the energetic flux to get life started. Sort of akin I guess to how the components of a lightbulb don't do anything until you add an electron flux.

I bought "The Vital Question" last year, but haven't read it yet. I started "Oxygen" by the same author though and found it a real slog. It felt like it occupied a hard position, assuming a fair amount of relevant scientific background in the reader, and wasn't really a book meant for general consumption. It's definitely possible I just wasn't in the right mental state for it.

Did you find his books to be like that? Have you read Oxygen by chance and good compare/contrast them?

I'll admit I haven't read them that recently but from what I recall the Vital Question is slightly more readable than Oxygen. That said, all of his books are very 'thorough' in the sense that he's definitely posing them as trying to make an argument as opposed to just educational, which does definitely make them less readable than they could be. Less bedtime reading and more something to actually make time for I guess?

I have seen him give talks in person before and they've been a lot clearer - maybe there's some on youtube? He's been on a few of the 'In Our Time' podcast episodes, so they might be interesting too?

I posted another comment above about recent discoveries that the Earth has enormous quantities of hydrogen deep underground which is constantly bubbling to the surface - and in fact, flowing all the way up to the upper atmosphere and even escaping into space (!). So this would indeed seem to provide a flux even deep underground. Understanding this geologic hydrogen cycle is a fascinating new field.

Yes this is definitely a theory already. The volcanic vents under the ocean particularly seem promising. I'm nowhere near qualified to even try to explain it without making certain errors, so I don't want to even try, rather I'll recommend someone who is qualified (and good at teaching).

If you're interested in this stuff, I can highly recommend Robert M. Hazen. He has an amazing Great Course called "The Origin and Evolution of Earth: From the Big Bang to the Future of Human Existence" that covers stuff in depth. There's a shorter one called "Origins of Life" as well but I haven't listened to that. My impression is that it's an abridged version of the former.

Hazen also wrote a book called "The Story of Earth: The First 4.5 Billion Years, from Stardust to Living Planet" which covers the same material as the course (but in book form, obviously) and is really good. I liked the lecture-style of the course better personally, but they're both excellent resources if you're interested in this stuff.

My only regret is that they're about 10 years old at this point. If anyone knows what has changed in the last decade in the field, I'd be fascinated to know.

Came here to post the same thing, The Story of Earth is excellent!

Oh thanks! I have an Audible subscription so just spent a credit on the Hazen great course.

Mind you, I just started the Bach and the High Baroque so it might be a fair way into 2024 before I get to it. Maybe I can interleave them...

Nice! I wouldn't worry too much. Once you start Hazen's course it will be impossible for you to stop :-D

That Bach course does seem quite interesting though, I'll check it out!

If you're interested in the origins and future of humanity, I'd recommend Isaac Arthur's YouTube channel as a complementary source as well.

https://www.youtube.com/@isaacarthurSFIA

Thanks, I'll check that out also!

Isaac Arthur is an engineer, so not exactly an expert on biology or anthropology. He does to a lot of futurology, but thats unrelated to the origins of life on earth and any speculation he does there is just that.

As a former astrobiologist, I respectfully disagree. The future and past are intimately related, and our planet's future may be examined through other planets' pasts (e.g. Venus). Other than genetics, we have zero evidence about life 3.5 billion years ago, so everything is speculation, and an engineer can do that as well as a biologist.

All life is made out of cells. All cells are filled with water. Phospholipids which make cells membrane arrange themselves into membrane because one part of them is hydrophobic and the other hydrophilic. Although I guess some water is present underground too.

Well that relates to something I heard a few years ago about there being more water in the earth's crust and mantle than in the oceans. Isn't there some SciFi book along those lines with the water rising up? Not something I've actually read, but I'm pretty sure I heard about it.

The water exists in the rock mostly like water exists in the silica packets in everything you buy these days -- chemically bound in hydrated forms of crystals. That means it must be taken into account in any chemistry models, but not that there's a giant reservoir underground waiting to burst out in a flood.

The essential ingredient for the origin of life is a source of energy.

The use of solar energy did not become possible until at least a few hundred million years after the appearance of life, perhaps only after more than a billion years, because the trans-membrane ionic pumps powered by solar light are extremely complex structures that could not have been created out of non-living substances.

The only known energy source that can cause the appearance of life is the reaction between dihydrogen (elemental hydrogen) and carbon monoxide or carbon dioxide. Carbon dioxide exists in huge quantities everywhere on any planet without living beings (Earth is an anomaly, because most of the original carbon dioxide has been reduced and incorporated in living matter), so what is necessary for the appearance of life is a source of free dihydrogen. A gradient of ionic concentration in water is also helpful.

Such conditions are present where either volcanic gases are released in water or in the so called alkaline vents, where rocks rich in iron are oxidized by water, releasing the hydrogen from water as dihydrogen (this is the "serpentinization" mentioned in the parent article).

Both kinds of conditions are more typical for certain places on the bottom of the ocean, but they can be also encountered under ground, with the condition that there must be water infiltrated through the rocks, without water there is no source of free dihydrogen.

> The only known energy source that can cause the appearance of life is the reaction between dihydrogen (elemental hydrogen) and carbon monoxide or carbon dioxide.

What do you mean by “the appearance of life”? These elements couldn’t make even a single amino acid, so I’m not sure I follow how these molecules could lead to the appearance of life.

In the presence of catalysts such as metallic sulfides, these produce complex hydrocarbons, and together with ammonia also the 10 primordial amino-acids that are abundant in abiotic environments.

All the complex organic molecules require energy for their production and only elemental hydrogen (reacting with the abundant carbon dioxide) or the less abundant carbon monoxide (reacting with the abundant water) can provide that in the absence of living beings.

The original source of energy that produces the free elemental hydrogen is the internal heat of the planet, which creates underground minerals that are stable at high temperatures, but unstable at low temperatures, so when they are exposed by volcanic processes to the water at the surface they are oxidized by the water, so they release the dihydrogen from water.

Since life cannot have existed from the Big Bang, it must obviously have appeared at some point in time after the formation of the planets.

It cannot have appeared in any place that does not provide the energy required for the synthesis of organic molecules, so the place where life has appeared must have included a source of dihydrogen (and carbon dioxide, but this is ubiquitous). Additional requirements are the presence of sulfides of iron, cobalt and nickel, which are necessary as catalysts, and also of water, ammonia and potassium ions (the latter are required to neutralize the organic acids that form much of the living matter; all the cells of all living beings are filled with potassium ions for this purpose). All these conditions are encountered in submarine alkaline vents or volcanic vents.

Wherever there exists air dissolved in the water, including at great depths in the ocean or underground, the bacteria and any other living beings obtain energy by the easier path of using dioxygen (elemental oxygen from the air) to oxidize either organic substances or inorganic substances, like elemental hydrogen or hydrogen sulfide. All such living beings, even if they live in the dark, depend on the solar energy captured by algae and plants, which have produced the free elemental oxygen.

At higher depths underground or in the marine sediments, where there is no longer enough air dissolved in the water, there are only bacteria that can use the energy of the reaction between dihydrogen and carbon dioxide. In some places where there is no air there are also sulfate-reducing bacteria, which use sulfate instead of carbon dioxide, but those are also indirectly dependent on photosynthesis, because the sulfate comes from other bacteria which live where there is air and which create the sulfate by oxidizing reduced sulfur compounds with oxygen from the air.

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