Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

The future lifespan of Earth’s oxygenated atmosphere

nature.com

Post reply on HN
Print view View original

41–50 of 90 posts

Re: The future lifespan of Earth’s oxygenated atmosphere

#41

Post by istjohn »

DavidSJ wrote: post #34
istjohn wrote: post #23

Interesting. Life emerged 4 billion years ago and the window of habitability for complex lifeforms will end in one more billion years. So terrestrial natural selection required 80% of the window of opprtunity to produce human intelligence. That's a tighter margin than I would have guessed.

This is predicted by the hypothesis that the origin of intelligent life requires the occurrence of several hard steps, each of which take at least several billion years (but with no upper bound) in expectation. If that hypothesis holds, then conditional on all the steps having completed on a given planet, they will have done so roughly equally spaced in the time allotted, regardless of their relative difficulty. So,…

Why do we think the origin of intelligent life requires a few hard steps and not just a continuous progression or perhaps one hard step and otherwise a steady progression?

Re: The future lifespan of Earth’s oxygenated atmosphere

#43

Post by AnIdiotOnTheNet »

vimacs2 wrote: post #29
devops000 wrote: post #5

Enough time to migrate to another planet.

It's literally enough time to even lift heavier elements from the Sun to extend it's stable life cycle by several billion years. Another commenter suggested moving the planet and got down voted to oblivion but it's not at all a ridiculous suggestion in these kinds of time scales. You could place giant ion thrusters on the moon and set it in an orbit where tidal effects would nudge the Earth outwards over a few millio…

The problem isn't the engineering, as usual, it's political. Can you realistically foresee humanity taking on such long term projects? We can't even get people to stop burning fossil fuels to "mine" cryptocurrency.

Re: The future lifespan of Earth’s oxygenated atmosphere

#44

Post by derekp7 »

Robotbeat wrote: post #35
excerionsforte wrote: post #13

I wonder if the great filter is not one, but multiple coincidences brought upon by "intelligent" life and the natural lifetime of a planet and/or solar system. If Mars had intelligent life and now it doesn't how does that bode for Earthlings? Can life really adapt given the lack of evidence anywhere? I wonder how will space travel to the next possible habitable planets work. Shoot in all directions and hope that life…

I think we can all but rule out a dead, ancient planet-spanning civilization on Mars now. We have medium resolution imagery of the entire planet and high resolution (meter or submeter) imagery of a lot of the surface, in a wide distribution. Mars hasn’t had enough volcanic activity to hide evidence of a planet-spanning civilization unless it occurred while large asteroid impacts were much more common. Venus, however,…

I always wondered what it would be like if Mars and Venus were swapped. Would Mars be warmer, or would it be even more devoid of atmosphere? And would Venus (with its greenhouse gas) be a more livable temperature if it was in Mars's orbit? It still wouldn't be survivable due to the atmospheric composition, but I was just wondering about raw climate.

Re: The future lifespan of Earth’s oxygenated atmosphere

#45

Post by istjohn »

AnIdiotOnTheNet wrote: post #43
vimacs2 wrote: post #29

Earlier quoted context omitted.

It's literally enough time to even lift heavier elements from the Sun to extend it's stable life cycle by several billion years. Another commenter suggested moving the planet and got down voted to oblivion but it's not at all a ridiculous suggestion in these kinds of time scales. You could place giant ion thrusters on the moon and set it in an orbit where tidal effects would nudge the Earth outwards over a few millio…

The problem isn't the engineering, as usual, it's political. Can you realistically foresee humanity taking on such long term projects? We can't even get people to stop burning fossil fuels to "mine" cryptocurrency.

Hell, we can barely get people to wear face masks in their neighborhood grocery store.

Re: The future lifespan of Earth’s oxygenated atmosphere

#46

Post by mannykannot »

Robotbeat wrote: post #40
vcdimension wrote: post #39

Earlier quoted context omitted.

burning carbon creates CO2, which would then get broken down back into oxygen (either by plants or directly by sunlight according to the article).

Plants require a certain temperature range to live (and also replenish CO2 slower than digging up and burning the carbon). And the sun directly is not very effective at producing oxygen. No discovered planet or exoplanet has an oxygen concentration like the Earth’s because it takes photosynthesis to be so extremely far from chemical equilibrium. UV dissociation just isn’t enough to get several psi of oxygen.

That is the sort of explanation I expected, but when I read the article, it presents a different causal sequence, in which photosynthesizing plants become ineffective, not because of increasing temperatures, but because of decreasing atmospheric CO2, as a result of its photodissociation. [1]

As presented in the news article, there is no explanation for why the apparently still-abundant oxygen does not react with, for example, the increased methane flux that the article also mentions, or just the carbon that has been liberated by dissociation, to maintain a CO2 level adequate for photosynthesis.

I don't doubt that the researchers have answers to these questions (quite likely the one you gave) but something seems to have gone missing in the creation of this news article.

[1] The article actually says "due to the gas absorbing the heat and breaking down", but AFAIK, CO2 is pretty resistant to this. Perhaps this is a garbled version of CO2 reacting more vigorously with rocks and soil at higher temperatures?

Re: The future lifespan of Earth’s oxygenated atmosphere

#47

Post by derekp7 »

taylodl wrote: post #20

As I understand it the sun has another 4.5 billion or so years of life remaining but the earth has only another billion years or so of being habitable. That's interesting. Complex life first appeared on earth about 2.5 billion years or so ago and has 1 billion more years to go for a total span of 3.5 billion years. In earth's projected 9 billion year lifespan it will only have been habitable for 3.5 billion years, or…

Is there enough selective pressure to keep human-style intelligence in the gene pool for another billion years? Look at the abundance of species on Earth, and only one species has a space program. Is there enough selective pressure for other species to eventually evolve advanced intelligence (considering how much of it that crows and dolphins have) or is it just an accident that humans have it, and it may not stay in our genes forever?

Re: The future lifespan of Earth’s oxygenated atmosphere

#48

Post by Robotbeat »

derekp7 wrote: post #44
Robotbeat wrote: post #35

Earlier quoted context omitted.

I think we can all but rule out a dead, ancient planet-spanning civilization on Mars now. We have medium resolution imagery of the entire planet and high resolution (meter or submeter) imagery of a lot of the surface, in a wide distribution. Mars hasn’t had enough volcanic activity to hide evidence of a planet-spanning civilization unless it occurred while large asteroid impacts were much more common. Venus, however,…

I always wondered what it would be like if Mars and Venus were swapped. Would Mars be warmer, or would it be even more devoid of atmosphere? And would Venus (with its greenhouse gas) be a more livable temperature if it was in Mars's orbit? It still wouldn't be survivable due to the atmospheric composition, but I was just wondering about raw climate.

The atmospheric composition is likely driven in part by the higher intensity of the Sun. At Mars, it’d have gotten a quarter of the sunlight. That means more water in its atmosphere (as there’s have been less UV to dissociate the water and less light pressure and less solar wind to blow the hydrogen away), less release of CO2 from carbonates, etc.

Re: The future lifespan of Earth’s oxygenated atmosphere

#49

Post by derekp7 »

istjohn wrote: post #41
DavidSJ wrote: post #34

Earlier quoted context omitted.

This is predicted by the hypothesis that the origin of intelligent life requires the occurrence of several hard steps, each of which take at least several billion years (but with no upper bound) in expectation. If that hypothesis holds, then conditional on all the steps having completed on a given planet, they will have done so roughly equally spaced in the time allotted, regardless of their relative difficulty. So,…

Why do we think the origin of intelligent life requires a few hard steps and not just a continuous progression or perhaps one hard step and otherwise a steady progression?

I think the hard steps are sharp divisions that had a long time in the status quo, then a sudden random development. Single-cell to multi-cellular. Development of nerve tissue that can collect information, make decisions, and influence the organism. Centralization of a bundle of nerves into a decision making center. Then you get to higher order steps that probably aren't as complicated, such as communications and organization, then all the steps that humans went through that took a while, without having major biological changes that enabled them.

Re: The future lifespan of Earth’s oxygenated atmosphere

#50

Post by ido »

derekp7 wrote: post #47
taylodl wrote: post #20

As I understand it the sun has another 4.5 billion or so years of life remaining but the earth has only another billion years or so of being habitable. That's interesting. Complex life first appeared on earth about 2.5 billion years or so ago and has 1 billion more years to go for a total span of 3.5 billion years. In earth's projected 9 billion year lifespan it will only have been habitable for 3.5 billion years, or…

Is there enough selective pressure to keep human-style intelligence in the gene pool for another billion years? Look at the abundance of species on Earth, and only one species has a space program. Is there enough selective pressure for other species to eventually evolve advanced intelligence (considering how much of it that crows and dolphins have) or is it just an accident that humans have it, and it may not stay in…

Evolution takes a very long time. If we manage to not kill our own civilisation we will be fine as our technology will advance many orders of magnitude faster than evolution will be able to cause any significant changes to our intelligence via natural selection.

Anatomically modern humans evolved 300k years ago and didn't change much since. Can you imagine what kind of progress we will make in the next 300k years? I can't even imagine the next 1000 years.

Post reply on HN