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Gamma-ray bursts are a threat to life

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Re: Gamma-ray bursts are a threat to life

#31

Post by eloff »

jjoonathan wrote: post #26
tectonic wrote: post #2

Is this the Great Filter?

Probably not. Life will find a way! > The bacterium Deinococcus radiodurans is the best known extremophile among the few organisms that can survive extremely high exposures to desiccation and ionizing radiation, which shatter its genome into hundreds of short DNA fragments2, 3, 4, 5. Remarkably, these fragments are readily reassembled into a functional 3.28-megabase genome. Here we describe the relevant two-stage DNA…

It's tough to imagine a similar process in a complex lifeform. So it could well be the great filter. Evolution doesn't work well with things that happen rarely over geological timescales. This is one reason why life on earth is very sensitive to climate change, even although the climate has gone through many major changes in the past.

Re: Gamma-ray bursts are a threat to life

#32

Post by TheDauthi »

pacala wrote: post #9
lucaspiller wrote: post #5

Let's assume this happened tomorrow, and it took another 500 million for life to evolve to what we would consider intelligent. Would anything of our civilisation be left? What would be the best way to leave a record that we existed?

Just keep going business as usual. Given that we have plenty of trilobite fossils from the Cambrian, might even expect future paleontologists to find some fossilized skulls. http://www.fossilmuseum.net/Paleobiology/CambrianFossils.htm

The only problem with this is that we might not have long enough for multi-cellular life to recover. While the red giant phase is a long way off, some scientists think that the carbon cycle could shut down as little as 500 million years from now, either due to oceanic evaporation or due to a failure in the weathering process.

Re: Gamma-ray bursts are a threat to life

#33

Post by cshimmin »

crystaln wrote: post #29

Is this really an explanation for the Fermi paradox? Would a factor of 0.1 or even 0.01 really change the import of the Fermi paradox?

It is complicated by the fact that this implies intelligent civilizations have a very finite window of opportunity in order to communicate. 500 Myr is a pretty short on cosmic timescale; so the odds that:

1) our civilization comes to exist in some 500Myr window

2) another civilization comes to exist in another 500Myr window

3) Signals sent from that other civilization arrive at the right time for ours to observe them

are considerably lower than just the odds that two civilizations develop that are advanced enough to communicate with each other.

Re: Gamma-ray bursts are a threat to life

#34

Post by Dylan16807 »

cshimmin wrote: post #33
crystaln wrote: post #29

Is this really an explanation for the Fermi paradox? Would a factor of 0.1 or even 0.01 really change the import of the Fermi paradox?

It is complicated by the fact that this implies intelligent civilizations have a very finite window of opportunity in order to communicate. 500 Myr is a pretty short on cosmic timescale; so the odds that: 1) our civilization comes to exist in some 500Myr window 2) another civilization comes to exist in another 500Myr window 3) Signals sent from that other civilization arrive at the right time for ours to observe them…

Those windows are pretty big. These aren't life-scouring cosmic rays, just mass extinctions. Complex life is still there, and can develop a civilization in a couple million years.

The reshuffling of life could even increase the chances of a civilization occurring. And a smart species has pretty good odds of surviving a mass extinction.

Re: Gamma-ray bursts are a threat to life

#35

Post by jjoonathan »

eloff wrote: post #31
jjoonathan wrote: post #26

Earlier quoted context omitted.

Probably not. Life will find a way! > The bacterium Deinococcus radiodurans is the best known extremophile among the few organisms that can survive extremely high exposures to desiccation and ionizing radiation, which shatter its genome into hundreds of short DNA fragments2, 3, 4, 5. Remarkably, these fragments are readily reassembled into a functional 3.28-megabase genome. Here we describe the relevant two-stage DNA…

It's tough to imagine a similar process in a complex lifeform. So it could well be the great filter. Evolution doesn't work well with things that happen rarely over geological timescales. This is one reason why life on earth is very sensitive to climate change, even although the climate has gone through many major changes in the past.

I wouldn't expect the ability to evolve in Eukaryotes if a GRB happened near Earth, but I see no reason why frequent GRBs in a distant galaxy would put a ceiling on complexity. Here's how I see it going down:

1. Life evolves. Not radiation resistant except for a group of bacteria that like to hang out in uranium-rich soil (or something).

2. GRB. Radiation-resistant bacteria repopulate the planet.

3. Radiation-resistant mechanism breaks in 99% of bacteria, but vestiges remain.

4. Mechanisms to handle bigger genomes evolve (Let's call them "eukaryotes" for the sake of the argument).

5. Single-celled "eukaryotes" invade the uranium-rich soil ecosystem by fixing the vestigial radiation resistant genes.

6. GRB. Radiation-resistant prokaryotes and radiation-resistant "eukaryotes" repopulate the planet.

7. Rinse, repeat.

8. Eventually there will be big multi-cellular radiation-resistant "eukaryotes" walking aroud.

----

> life on earth is very sensitive to climate change

We are very sensitive to climate change, as are a bunch of higher organisms we care greatly about. Life on Earth? Not a chance. We couldn't come close to sterilizing the planet if we wanted to.

Re: Gamma-ray bursts are a threat to life

#37

Post by slackson »

mahranch wrote: post #27
api wrote: post #24

Earlier quoted context omitted.

It is, but on a side note: If you actually had the technology to accelerate to a speed close to light, time dilation might actually allow you to make an intergalactic journey as long as you were okay with leaving behind your home forever... Since a few years for you might be tens of millions of years elsewhere. There is also little matter between galaxies, so the hyper velocity particles problem would be less severe.…

The issue with Fermi's Paradox is the fact that it's not a paradox at all. It relies on assumptions and presumptions that are now dated (we have explanations for). For starters, let's begin with the first point it makes; If there are a bunch of civilizations out there, why haven't we heard them yet? That's the wrong question. It makes an incorrect presumption; Why should we have heard them? Do you think a highly adva…

I'm not so sure about your conclusion there. The galaxy is around 100k light years across. Seems like a lot, but the Orion project looked like it could potentially reach speeds of 10% the speed of light. Even assuming that's optimistic, and it could only get to 1% the speed of light on average, that's just ten million years.

Re: Gamma-ray bursts are a threat to life

#39

Post by nerfhammer »

crystaln wrote: post #29

Is this really an explanation for the Fermi paradox? Would a factor of 0.1 or even 0.01 really change the import of the Fermi paradox?

Yes, because these events may have been much more frequent in the early universe

http://www.nature.com/scitable/blog/postcards-from-the-unive...

http://arxiv.org/abs/astro-ph/9901322

Re: Gamma-ray bursts are a threat to life

#40

Post by vorg »

Dylan16807 wrote: post #34
cshimmin wrote: post #33

Earlier quoted context omitted.

It is complicated by the fact that this implies intelligent civilizations have a very finite window of opportunity in order to communicate. 500 Myr is a pretty short on cosmic timescale; so the odds that: 1) our civilization comes to exist in some 500Myr window 2) another civilization comes to exist in another 500Myr window 3) Signals sent from that other civilization arrive at the right time for ours to observe them…

Those windows are pretty big. These aren't life-scouring cosmic rays, just mass extinctions. Complex life is still there, and can develop a civilization in a couple million years. The reshuffling of life could even increase the chances of a civilization occurring. And a smart species has pretty good odds of surviving a mass extinction.

To survive a mass extinction from gamma-ray bursts, a smart species would build a self-sustaining subterranean city with 1 million humans in residence at any one time, perhaps rotating in and out on tours. I'm sure the Chinese will have one within 50 years even if no-one else does. And such subterranean cities are also likely how humans will be living on Mars for thousands of years before it's terraformed.
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