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

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

#181

Post by hotstickyballs »

mr_mitm wrote: post #38
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…

The Goldilocks zone doesn't enter the Drake equation at all. As a reminder, this is the equation: https://en.wikipedia.org/wiki/Drake_equation#Equation It makes very few assumptions.

The biggest assumption is that it assumes only a single path to intelligent life.

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

#182

Post by mkl »

kulahan wrote: post #150
tastyfreeze wrote: post #135

Earlier quoted context omitted.

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.

There's not much difference between now and 3.5-3.8 billion years ago, but before that there were a lot more: https://en.wikipedia.org/wiki/Late_Heavy_Bombardment

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

#183

Post by pfdietz »

runarberg wrote: post #176
pfdietz wrote: post #167

Earlier quoted context omitted.

Your argument shows a lack of understanding of exponential growth. Any given colony has to create only slightly more than 1 additional colony in order to drive exponential growth. There doesn't have to be any coordinated action by a central authority for it to happen. For it not to happen (if it is physically feasible), in contrast, every species has to refrain from doing it at all points in their history, almost wit…

Permanent exponential growth is very rare in nature, and even rarer in biological systems. What we observe as exponential growth is usually only a partial observation of a logistical curve or is missing a system collapse at the end of the curve. We have no reason to believe alien (or even human) civilization will continue to grow and expand forever. Heck even the human population curve has started to slow down and is…

It's rare in biological systems because it's terminated by running out of some resource.

But you're saying galactic colonization would terminate without running out of new systems to colonize.

There would be a slowdown due to geometric constraints -- only so many new systems adjacent the boundary of the colonized zone -- but that hardly solves your problem.

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

#184

Post by andrewflnr »

tim333 wrote: post #172
andrewflnr wrote: post #57

I've tried reading the paper, which is obviously less hand wavy than this mess of a blog post but pretty tough going for a layman. I still don't see how they conclude that the water arrived all at once instead of in a bunch of comets... https://www.science.org/doi/10.1126/sciadv.adw1280

The >Our Solar System formed around 4,568 million years ago. Considering that it only took up to 3 million years to determine the chemical properties of the Earth sounds suspiciously precise. You'd imaging the proto Earth would have formed gradually over millions of years from rocks and dust merging rather than suddenly there 4,568 m years ago and then shortly after crashed into?

Well, 3 million is "millions". Anyway, that very quote continues:

> "...this is surprisingly fast," says first author Kruttasch.

So they don't entirely disagree that it's weird.

But why are you replying to me with a quote from the article I already called a mess? Try your hand at the paper if you want real answers. :D Like I said, tough going, but they sure seem to think they have the sigfigs to back it up.

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

#185

Post by jcims »

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…

Bit of a nit but the Drake equation is intended 'to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way Galaxy' (from the Wikipedia entry for it). Nice thing is that you can drop a few terms to get to origin of life.

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

#186

Post by 29athrowaway »

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…

Mars is technically in the goldilocks zone of the solar system... but water on Mars boils at 0C or 32F due to low atmospheric pressure, which really sucks.

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

#187

Post by mianos »

DennisP wrote: post #154
buran77 wrote: post #45

Earlier quoted context omitted.

The equation itself makes no assumptions. But anyone trying to calculate something with it must. The last five factors in the equation will be filled in by assumptions based entirely on one data point, life on Earth. From your link: ne = the average number of planets that can potentially support life per star that has planets. fl = the fraction of planets that could support life that actually develop life at some poi…

One approach is to give each variable a probability distribution. The greater our uncertainty about possible values, the wider the bell curve. Drexler and colleagues did that, and found "a substantial probability that we are alone in our galaxy, and perhaps even in our observable universe (53%–99.6% and 39%–85% respectively). ’Where are they?’ — probably extremely far away, and quite possibly beyond the cosmological…

A probability distribution describes how likely different outcomes are. It requires multiple observations or an assumed model that can represent variability.

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

#189

Post by renshijian »

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…

A brilliant summary! You've deepened the question from "Does a habitable planet exist?" to "Does a planet successfully complete the complex dynamics of life's origin?" The habitable zone is merely the ticket, while the conditions you mention are the truly demanding filters. Considering this, the probability of our existence truly seems miraculous

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

#190

Post by Shekelphile »

macintux wrote: post #109
echelon wrote: post #68

Earlier quoted context omitted.

And you have to have multiple low probability events. These probabilities multiply. We had a good start. A Jupiter to clear the debris, a Theia impact to create tides and contribute to tectonics, a magnetic core, a shielded atmosphere. We had water delivered to us. Maybe even panspermia. Maybe cell walls and mitochondria are hard. Maybe multicellular is hard. Maybe life on land is hard. Building lungs, rebuilding eye…

My pessimistic side says that the conditions for intelligent life are so implausible that we’re unique, and when we drain the planet dry of easily-accessible fossil fuels we’ve deprived any successor civilization of its opportunity to escape the planet. Basically I fear we’re the universe’s only shot of appreciating and populating the galaxy (or beyond) and we’re on the brink of throwing that away.

> when we drain the planet dry of easily-accessible fossil fuels we’ve deprived any successor civilization of its opportunity to escape the planet.

There will be no successor civilization to humans. Earth won't be able to support multicellular life in a few hundred million years due to the sun becoming gradually more luminous over time, resulting in higher surface temperatures that will eventually culminate in a runaway greenhouse happening, as it already has on Venus. Due to human-driven climate change effects this event will certainly happen much sooner (Even if life evolving on earth was an incredibly rare event the chance of such circumstances not happening elsewhere even in our own galaxy is infinitely small - there are trillions of planets and 100b+ stars. On top of that there are 100s of billions of galaxies within the observable universe as well.

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