The sun was dimmer when earth formed – how did life emerge? | Hacker News Reader

The sun was dimmer when earth formed – how did life emerge?

quantamagazine.org

68 pointssdht039 comments

Neither this article nor the wikipedia entry[1] contain the string "geothermal". A web search[2] seems to return some stuff. Both sources of geothermal heat (residual heat from the planet's formation and nuclear decay heat) were greater in the distant past, to my understanding...

[1] https://en.wikipedia.org/wiki/Faint_young_Sun_paradox

[2] https://www.google.com/search?q=faint%20young%20sun%20geothe...

Yeah I thought it was accepted it likely emerged around vents and spread upwards slowly. Iirc the earth was hit with a ton more radiation back then as the ozone layer was created when creatures moved up and evolved to use the suns light as an energy source (photosynthesis.)

I’m also a layman so this could be outdated or potentially wrong

Sure, but that’s not a huge effect. The Sun hits us with 125-150Petawatts of solar energy, was about 15% cooler when life developed (~20PW), and the amount of heat the Earth emitted from radioactive decay was at most about a factor of 1000 times less (~120TW) around the time life developed.

Even the energy released by the Earth cooling and solidifying over 100 million years still only comes down to like 1-2 Petawatts except immediately. And to try to make up another 10PW from bombardment heating would require About 1000 cubic kilometers of infalling asteroids per year (more than a Moon’s worth of mass over 100 million years), so Earth should’ve become pretty frigid soon after solidifying… UNLESS there was significantly more greenhouse effect back then (which is most likely!).

That slight increase in earth's internal heating can have an outsized effect. It would have meant more and different volcanism, which means a different atmosphere which, perhaps, was better at absorbing and retaining heat.

Yeah, the atmosphere is by far the biggest effect. Geothermal heating (especially by radioisotopes) is a rounding error in this case.

It’s also directly meaningful difference because ice floats and provides insulation. Even a runaway greenhouse atmosphere provides nowhere near as much insulation as a 1km thick ice sheet. Seemingly minimal amounts of geothermal heat should provided thousands of cubic km worth of oceans for life to live in during the three snowball earths believed to have happened.

This is also why Europa’s −171 °C surface temperature is believed to give way to liquid oceans.

Those numbers look right, thanks. Looks like about 3x the radiogenic heat from the major nuclides producing heat today (not taking into account nuclides that may have decayed away... but I don't think there were any substantial ones). There's also the possibility of fission chain reactions, as U235 enrichment was very high, but I doubt these came near the PW range. Atmospheric CO2 looks like the primary factor.

Sure, but the amount of 70F water that lasted for more than a decade might have been 1000x higher because of increased geysers, volcanoes, deep sea vents etc. Sure it might have been a vanishingly small fraction of the earth's surface and oceans, but still have an impact on the evolution of life while the earth was on average quite cool.

All this assumes that life had to form on the surface. But that's not the only possibility. If life formed deeper in the Earth and migrated to the surface later, the fainter sun might not have been an issue. Geothermal energy is small on the surface, but not deeper down.

My reading of the article is that scientists are puzzled by the the evidence for large amounts of liquid water, not just life. If you look back in the past and see ice, but also life, geothermal is relevant. But they see rivers and oceans, so you have to focus on bigger solutions.

Is that 15% of it's current value, or 15% lower? Because 15% lower its more like 100petawatts.

Mind you, the bigger question is where the entropic difference was. The earth, including the water would all still be warmer while cooling down, and it needs to drop that heat somewhere for life to do it's entropic increases

Equally the earths core and mantel being closer to it's formation, would of been hotter. So heat levels would of been offset perhaps by that aspect. Then the atmosphere would of been different.

Those are two area's that I'd like to see data upon.

After all, the Earth was a molten ball that slowly cools and you can't overlook that nuance over time. Which may of well balanced out the suns output levels for surface temperatures. Certainly volcanic activities and techonomic plate activities were far more active in the early days of Earth.

https://en.wikipedia.org/wiki/Earth%27s_crustal_evolution seems a good read in conjunction with this article.

Hey, just a friendly clarification from the neighborhood grammar police - "would of" should be "would've" or "would have."

No offense intended!

Additionally, “mantel” should be “mantle” if referring to the thing underground. “Area's” should be “areas”, “suns” should be “sun's”, “techonomic” should be “tectonic”, and “may of well” should probably be “may well have”. (“may have well” might be fine.)

These things don't matter all that much, though. The meaning's clear enough, apart from maybe “techonomic”.

Techonomic activity could be earthquakes in silicon valley.

No offence and my humble apologies.

I will confess that English grammar and spelling is kryptonite for me, and maybe down to my autism and over logical mind with a language that has so many exceptions.

Again, no offence and anybody who points out and explains what was wrong is always welcome and appreciated, as constructive and helpful feedback is how we learn. I will confess, the whole "would of" is one I keep doing, and something I should make more effort upon, and will.

Many thanks for taking the time.

FWIW I downloaded Grammarly free edition, for the best. Though any alternative suggestions are greatly appreciated.

Grammarly is worse than useless, in my experience. Half of its suggestions turn correct grammar into incorrect grammar. (Though it does catch the obvious stuff.)

I did catch a few changes it recommended that did not work. Though it is better than my own, obvious shortcomings. When I was at school(70's 80's), I thought such grammar and spelling correction would be easily automated away and yet.

Though it may not be perfect, it is testament how hard grammar can be, translated into a rule set.

> I will confess that English grammar and spelling is kryptonite for me

English is an amalgamation of about five different languages from at least three different families at this point, so I think we can all be forgiven for getting these things wrong every now and then. :)

(Linguists: Don't take "five" and "three" too literally.)

"would of" is one many native English speakers also regularly make. Your written English seems above average to me.

I am not sure if this can be stopped at this point. Too many people are already writing “should of”. Same for excessive apostrophe’s.

That effect is much, much smaller over periods of 100 million years than a stronger greenhouse effect. Geothermal Too small to explain the difference. See my post: https://news.ycombinator.com/item?id=30120710

I recommend https://youtu.be/vAgiHreswj0 for a history of the estimated age of the earth.

Indeed, it's been theorized by many that life actually started at the deep sea hydrothermal vents. It's rich in energy, metals, etc. Even if not started there, there was a period where nearly the entire planet was under ice, and might have acted as a reservoir.

On the scale of billions of years the earth spun more quickly, and the moon was significantly closer (and reflected more light on earth).

Seems reasonably to expect there where more volcanoes, more hydrothermal vents, more earthquakes, and more tectonic activity of all kinds earlier in the earths history. Not to mention early in earth's history the late heavy bombardment. All making potential hospitable environments even if the earth was on average cooler than ideal.

On the flip side the moon is going to keep getting further from the earth, as energy transfer via tides increases the moons velocity ... until 1 day = 1 lunar month. Thus the need for occasional leap seconds as the earth spins more slowly. Afterwards the moon will slowly decrease it's orbit because until it kits the Roche limit and turns into a ring ... unless the sun expands enough before then, which is the time scale of these changes.

The article doesn't mention it, but is it possible the Earth was slightly closer to the Sun when the solar system formed? I'd say assuming it was always at 150m km is doubtful.

Possibly, that and rotation speed, size of the sun! Many factors just not touched upon. Indeed, way more asteroid impacts as well and with that, energy put into the Earth.

Good points! I also like the others raised in the comments, as it paints a picture of a very complex process.

All these theories assume that life emerged on Earth, from scratch. But what if it didn't? What if it got here in a meteorite for example and then started evolving because of a favorable environment? Some bacteria are capable of surviving extreme conditions, so that's a possibility. And, there were cases when meteorites contained some of molecules (I don't remember which exact ones) that are basic building blocks of life as we know it.

Not to say it's not impossible, but isn't your hypothesis much less plausible than the alternative?

Why is it much less plausible? It's important to explore alternate possibilities when we aren't 100% sure of something. For way too long we've thought that Earth was the center of the solar system and the universe, only to later find out that it's just one of the planets in one of zillions of star systems.

Also I'm somehow pretty sure JWST would change our understanding of the universe. (we'll see in a year how well this comment ages)

Less plausible since we know what kind of conditions asteroids go through, along with what conditions things outside of a rock in space close to the sun would go through

Also: the speed of light barrier and age of the universe. It takes a LOT of energy or a LOT of time to get from one place to another.

> age of the universe

We'll see how this goes when JWST begins its observations.

And then what's a LOT of time to a human is a blip on the cosmic scale.

The Earth had a faster rotation speed so its thermal equilibrium average temperature was higher (compared to if it spun like it does today). Look at the quartic term in the Stefan Boltzmann law and think about how that interacts with the Jensen inequality.

> We know that life under our faint young sun was possible, and now we might know why. What we are starting to see is just how lucky we may have been in avoiding becoming a permanent snowball Earth or even a steam Earth. Somehow, conditions were just right on our planet, keeping us in this narrow window between being frozen solid and evaporating to oblivion, and allowing us to survive — despite a few near misses. “There’s a huge discussion about the requirements for habitability,” said Feulner. “Even on Earth, things could have gone wrong easily.”

On the other hand, why hasn't life colonized the arctic?

(Yes, I know about penguins and polar bears. I would expect more than that.)

Also at higher altitudes.

There’s plenty of life in the arctic (and Antarctic) sea. On land it’s a desert. It’s about as hospitable as the Sahara.

> It’s about as hospitable as the Sahara.

Meaning life hasn't adapted to it. My point exactly.

(The seas don't get below freezing.)

I wonder if Heller’s solution mentioned in the article also tackles the lunar inclination problem.

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