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

Earth was born dry until a cosmic collision made it a blue planet

sciencedaily.com

Post reply on HN
Print view View original

141–150 of 279 posts

Re: Earth was born dry until a cosmic collision made it a blue planet

#141

Post by mr_toad »

corimaith wrote: post #130
JamesLeonis wrote: post #35

Earlier quoted context omitted.

The Drake Equation is filled with assumptions, like life must appear on a planet in the Goldilocks zone of a star. The whole equation has only one datapoint to extrapolate from. Tweak the equation's parameters and it will predict universes that only have one civilization per galaxy or worse! We have no way of knowing what those parameters are because we haven't seen other examples. A major reason we are interested in…

Even if you only had a handful of civilizations, the sheer time that has passed and size of the universe should mean that life should still be alot more apparent. With sublight velocities achievable today, I recall it would only take around a million years for a Von Newmann probe to cover the entire galaxy. Such a probe is quite conceivable, so why isn't there more evidence of such probes everywhere? Another point I…

At some point replicative drift will set in. How many replications is two million years? How long before the probes evolve? How long before they speciate? How long before a species turns on itself?

Re: Earth was born dry until a cosmic collision made it a blue planet

#142

Post by mr_toad »

tshaddox wrote: post #64
HarHarVeryFunny wrote: post #40

Earlier quoted context omitted.

The thing is that even for a super low probability event, the size of the universe is so huge and such events must be happening all the time. e.g. Say chance of a random planet ever being hit by a water-carrying comet is one in a billion, then with 100B - 1T planets in the milky way it'd happen here 100-1000 times. If chances are only one in a trillion, and we're the one in the milky way, then there are still another…

> The thing is that even for a super low probability event, the size of the universe is so huge and such events must be happening all the time. But numbers can go arbitrarily low.

> But numbers can go arbitrarily low.

Which begs the question, why 1, and not zero? I can buy zero, or a very large number. But 1 exactly? Nature doesn’t do that.

Re: Earth was born dry until a cosmic collision made it a blue planet

#143

Post by Animats »

caymanjim wrote: post #41
xbmcuser wrote: post #18

Earlier quoted context omitted.

Your assumption we need water for life to exist is in my opinion wrong. We only know Earth so assume that is what is needed for life to exist.

There's a reason life is carbon-based, and it's not random. It's the only element that works, due to abundance; ability to form many bonds; bonds that are just durable enough but not too durable. There's plenty of sci-fi about silicon-based life, but that's infeasible fantasy. And no other elements have any hope. If you have carbon-based life, you need water as solvent and medium. It's a pretty safe assumption that a…

> There's plenty of sci-fi about silicon-based life, but that's infeasible fantasy.

Right. Silicon dioxide is quartz.

Longer analysis.[1]

[1] https://www.the-ies.org/analysis/does-silicon-based-life-exi...

Re: Earth was born dry until a cosmic collision made it a blue planet

#144

Post by macintux »

HarHarVeryFunny wrote: post #138
macintux wrote: post #132

Earlier quoted context omitted.

None of which are, I assume, as easy/efficient/effective to integrate into a new civilization's tech tree as coal & oil.

What has that got to do with energy dense rocket fuels for getting to orbit ?!

The key phrase was "successor civilization".

Re: Earth was born dry until a cosmic collision made it a blue planet

#145

Post by mr_mitm »

the_af wrote: post #60
mr_mitm wrote: post #48

Earlier quoted context omitted.

Thanks, I read that part before I shared it. It's pretty clear to me, these are pretty well defined quantities, just hard to measure. What is unclear is perhaps the definition of life. But at no point does it assume a planet must be in the Goldilocks zone. So perhaps you want to point out those assumptions you are talking about to me, because I don't see them. Edit: the parent post has been edited substantially after…

How can you extrapolate those terms from a single planet with known life without making assumptions?

I can't, but the equation itself doesn't to that. The assumptions are up to the reader to make. That's why I think that the equation isn't particularly useful.

Re: Earth was born dry until a cosmic collision made it a blue planet

#146

Post by DennisP »

LeifCarrotson wrote: post #125
dotancohen wrote: post #115

Earlier quoted context omitted.

About forty years ago I read a terrific book about life forms that live on a star. Maybe Starquake was it called? Did to the abundance of energy on the surface of a star, they live their lives a million times faster than humans. Thus for both them and the humans who discover them, communication is difficult. I think the humans push these life forms to develop civilization, which from the human's perspective had them…

That's "Dragon's Egg" by Robert L. Forward, a classic Sci-fi story: https://annas-archive.org/md5/4c381ac344506d10037fc8e7747098... The cheela lived on the surface of a neutron star, and they lived faster because the nuclear physics that powered their metabolism are far faster than the chemical and mechanical physics that power our own.

There's also Sundiver by David Brin, which has plasma life forms in our sun.

Re: Earth was born dry until a cosmic collision made it a blue planet

#147

Post by DennisP »

mr_mitm wrote: post #44
crazygringo wrote: post #39

Earlier quoted context omitted.

I'm assuming they were referring to this term: > n_e = the average number of planets that can potentially support life per star that has planets. The fact that the planet is neither too hot nor too cold would seem to be a major component of this term: https://en.wikipedia.org/wiki/Habitable_zone

That's just your interpretation. Take the equation at its face value and it does allow for life originating around some deep sea vents, like JamesLeonis speculated.

It does seem unlikely that such life forms would ever become spacefaring.

Re: Earth was born dry until a cosmic collision made it a blue planet

#148

Post by mr_toad »

quotemstr wrote: post #127
shireboy wrote: post #4

This could mean in the Drake equation ne -number of planets capable of life- is very small. A planet has to be hit with a comet big enough to deliver a large amount of water but not so big or fast to destroy it. And be in the Goldilocks zone of the star. Also the mass of the planet would play a part - gravity of more massive ones would be more likely to capture a comet. But again, too massive and I could see that ham…

Planetary collisions happen all the time . All of Mercury, Venus, Earth, and Mars in our solar system had them. We can see their signatures in other solar systems too: see https://en.wikipedia.org/wiki/List_of_extrasolar_planetary_c... Whatever the great filter is, it's not planetary-scale collisions during the accretion phase of solar system formation.

A couple of dozen collisions out of 6000+ known exoplanets. Not exactly common, but not freakishly rare either.

Re: Earth was born dry until a cosmic collision made it a blue planet

#149

Post by kulahan »

mr_toad wrote: post #137
kulahan wrote: post #133

Earlier quoted context omitted.

Don’t forget this can only happen once, really. You need it to be such a rare event that it doesn’t keep sanitizing the planet with repeated impacts, but one really perfect strike will bring what you need and allow life to form. The number of instances where this (something unreasonably unlikely) happened in our cosmological history is kinda surprisingly high. I’m absolutely convinced there’s no advanced life (and CE…

> Suddenly, high adaptability and intelligence and resilience was what mattered, and being big and strong suddenly was a massive disadvantage. Maybe it was just being small, puny, and having a tendency to cower in burrows was what saved us. Our ancestors may not have been much smarter than squirrels, and squirrels aren’t very bright. Hominids brains didn’t get big until long, long after the KT extinction. A Tigers br…

Correct - that’s what SAVED us. What allowed us to thrive and dominate the planet was what I mentioned.

It may be more correct to say that growing a larger brain (larger than a lizard’s, I mean) was only realistically possible because of the sudden loss of predators.

Re: Earth was born dry until a cosmic collision made it a blue planet

#150

Post by kulahan »

tastyfreeze wrote: post #135
kulahan wrote: post #133

Earlier quoted context omitted.

Don’t forget this can only happen once, really. You need it to be such a rare event that it doesn’t keep sanitizing the planet with repeated impacts, but one really perfect strike will bring what you need and allow life to form. The number of instances where this (something unreasonably unlikely) happened in our cosmological history is kinda surprisingly high. I’m absolutely convinced there’s no advanced life (and CE…

Earth has been struck by large comets many times killing the majority of life on the planet each time. In an early solar system it would be more frequent. Once a comet impacts there is one less comet out there. The solar system cleans up over time making impacts less likely over time.

There isn’t that much of a difference in the number of comets in space across just 5 billion years.
Post reply on HN