Freethought & Rationalism Archive

David M. Payne · 02-20-2003, 01:04 AM

How long until the earth is uninhabitable? I don't mean by the misdeeds of humanity, who knows if/when that will happen, but when the sun starts dying and it starts heating up the atmosphere etc. I remember reading it somewhere, but I can't find the source now, anyone here know the answer?

David

Secular Pinoy · 02-20-2003, 02:22 AM

The Earth is barely inhabitable now!

Actually, when the Sun's core starts helium fusion, in about 5 billion years. That would cause the Sun's outer shell to expand beyond Venus' orbit and fry the Earth.

Friar Bellows · 02-20-2003, 04:10 AM

Some scientists reckon we've only got 500 million years left, long before the Sun becomes a red giant. The argument goes that since the Sun is slowly getting brighter with time, within a billion years or so the temperatures on Earth will become so high that the oceans will evaporate. But before then, CO2 levels will drop in response to the Earth becoming drier and drier, and by around 500 million years, plants will no longer be able to survive. I wish I could find a link for this, but I can't.

Secular Pinoy · 02-20-2003, 05:33 AM

Is the slow brightening of the sun a steady increase, or more of a fluctuating one? I'm asking because it sounds, somewhat, like the creationists' "shrinking sun" argument. The idea is intriguing nonetheless.

braces_for_impact · 02-20-2003, 05:46 AM

Ah! We'll be smacked by an extinction event comet/asteroid long before that...

doghouse · 02-20-2003, 06:09 AM

Quote:

Originally posted by Secular Pinoy
Actually, when the Sun's core starts helium fusion, in about 5 billion years. That would cause the Sun's outer shell to expand beyond Venus' orbit and fry the Earth.

Uh oh, I'm going to need more duct tape.

Feather · 02-20-2003, 06:13 AM

Quote:

Originally posted by Secular Pinoy
Is the slow brightening of the sun a steady increase, or more of a fluctuating one? I'm asking because it sounds, somewhat, like the creationists' "shrinking sun" argument. The idea is intriguing nonetheless.

The gravitational interaction and the degeneracy "reactions" (can only fit so many fermions and bosons in a given space for a given force/volume constraint) result in a slow, steady compressing of the bits comprising the sun. The intensity of emitted light increases in the same way, cuz this is determined in part by the density of matter.

The mass of the star determines how long this process goes on as the more massive the star the more gravitational collapse occurs. Our sun will (likely) eventually reach a maximum intensity of emission before exploding into a red giant, spewing plasma and other bits well into the inner solar system and annihilating any life therein (if any remains as per the above posters' comments).

Secular Pinoy · 02-20-2003, 06:18 AM

Ha! I don't think The Nemesis Meteor would be able to bother us, we will have the International Space Station built by then (hopefully), and it's just the thing to stop that wayward piece of rock. How? Not by launching interstellar ballistic nukes from the ISS. No sir, that would be too easy. I say we rig the ISS with nukes and just use it to ram the damn thing. Who says the ISS is useless?

Jesse · 02-20-2003, 07:14 AM

Here's a great book on earth's future:

The Life and Death of Planet Earth

Apparently within a mere 100 million years carbon dioxide levels will be low enough (barring intelligent intervention) that the majority of modern plants will die out, but a group of plants called monocots (which includes grasses, palm trees, and bamboo) have evolved a more efficient form of photosynthesis which will allow them to live another 400 million years or so.

It's interesting that, given that the earth is around 4.5 billion years old, intelligent life seems to have evolved "just under the wire"...an example of the anthropic principle, maybe? See Robin Hanson's article on "the Great Filter" here:

http://hanson.gmu.edu/greatfilter.html

Quote:

Consider a situation where a certain number of trial and error steps must be completed in a certain order within a certain total timewindow. That is, for each step there is some constant probability per unit time of completing that step, given that the previous step has been completed. If the probability of completing all the steps within the time window is low, then it turns out that for the cases where all the steps are in fact completed, the average time to complete each "hard" step is unrelated to how hard that step is!

For example, say you have one hour to pick five locks by trial and error, locks with 1,2,3,4, and 5 dials of ten numbers, so that the expected time to pick each lock is .01,.1, 1, 10, and 100 hours respectively. Then just looking at those rare cases when you do pick all five locks in the hour, the average time to pick the first two locks would be .0096 and .075 hours respectively, close to the usual expected times of .01 and .1 hours. The average time to pick the third lock, however, would be .20 hours, and the average time for the other two locks, and the average time left over at the end, would be .24 hours. That is, conditional on success, all the hard steps, no matter how hard, take about the same time, while easy steps take about their usual time (see Technical Appendix). And all these step durations (and the time left over) are roughly exponentially distributed (with standard deviation at least 76% of the mean). (Models where the window closing is also random give similar results.)

We can apply this model to the evolution of life on Earth, by examining the fossil record for roughly equally spaced apparent major innovations. Such an analysis can complement other attempts to find hard steps by intrinsic difficulty, necessity, and uniqueness in evolutionary history, such as attempted in [Barrow & Tipler 86]

Craig · 02-20-2003, 08:36 AM

Quote:

Originally posted by Jesse

Apparently within a mere 100 million years carbon dioxide levels will be low enough...

Nah, we just rejected the Kyoto treaty so we're good.

That number seems awfully low to me, 100 million years is not long at all. Is there some graph showing why they picked that number, that shows the rate of change of the CO2 level?

02-20-2003, 01:04 AM	#1
David M. Payne Veteran Member Join Date: Oct 2000 Location: The land of chain smoking, bible thumping, holy ro Posts: 1,248	How long until the earth is uninhabitable? How long until the earth is uninhabitable? I don't mean by the misdeeds of humanity, who knows if/when that will happen, but when the sun starts dying and it starts heating up the atmosphere etc. I remember reading it somewhere, but I can't find the source now, anyone here know the answer? David

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02-20-2003, 02:22 AM	#2
Secular Pinoy Veteran Member Join Date: Feb 2001 Location: Quezon City, Philippines Posts: 1,994	The Earth is barely inhabitable now! Actually, when the Sun's core starts helium fusion, in about 5 billion years. That would cause the Sun's outer shell to expand beyond Venus' orbit and fry the Earth.

02-20-2003, 04:10 AM	#3
Friar Bellows Veteran Member Join Date: Apr 2001 Location: arse-end of the world Posts: 2,305	Some scientists reckon we've only got 500 million years left, long before the Sun becomes a red giant. The argument goes that since the Sun is slowly getting brighter with time, within a billion years or so the temperatures on Earth will become so high that the oceans will evaporate. But before then, CO2 levels will drop in response to the Earth becoming drier and drier, and by around 500 million years, plants will no longer be able to survive. I wish I could find a link for this, but I can't.

02-20-2003, 05:33 AM	#4
Secular Pinoy Veteran Member Join Date: Feb 2001 Location: Quezon City, Philippines Posts: 1,994	Is the slow brightening of the sun a steady increase, or more of a fluctuating one? I'm asking because it sounds, somewhat, like the creationists' "shrinking sun" argument. The idea is intriguing nonetheless.

02-20-2003, 05:46 AM	#5
braces_for_impact Veteran Member Join Date: Apr 2002 Location: In a nondescript, black helicopter. Posts: 6,637	Ah! We'll be smacked by an extinction event comet/asteroid long before that...

02-20-2003, 06:18 AM	#8
Secular Pinoy Veteran Member Join Date: Feb 2001 Location: Quezon City, Philippines Posts: 1,994	Ha! I don't think The Nemesis Meteor would be able to bother us, we will have the International Space Station built by then (hopefully), and it's just the thing to stop that wayward piece of rock. How? Not by launching interstellar ballistic nukes from the ISS. No sir, that would be too easy. I say we rig the ISS with nukes and just use it to ram the damn thing. Who says the ISS is useless?

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