Ison

True enough, but the advent of farming did indeed make sure that more humans reached the age of reproduction to pass on their genes. I'm just saying we (as a species) have evolution to thank for enabling us to provide life-saving or life-extending technologies into use, like agriculture, medicine, etc., but for higher-tech applications of science, evolution won't help much, because it is not all that crucial to know more about the atom's nucleus or to know more about space travel in order to ensure our survival to pass on our genes to the next generation.

In fact, "knowing too much" might preclude passing on our genes. Naturally, I'm speaking of individuals, not as an entire species. Technological knowledge may indeed help to ensure that more humans live longer to pass on genes. But evolution doesn't need to give us ALL bigger brains... just enough to ensure that the ones that do come along get used to help all of us.

Originally posted by Suzianne
True enough, but the advent of farming did indeed make sure that more humans reached the age of reproduction to pass on their genes. I'm just saying we (as a species) have evolution to thank for enabling us to provide life-saving or life-extending technologies into use, like agriculture, medicine, etc., but for higher-tech applications of science, evolutio ...[text shortened]... ger brains... just enough to ensure that the ones that do come along get used to help all of us.

True enough! It won't be evolution applications that will get us off this nice nest of a planet into space where the human race might survive a world wrecking catastrophe, a step up from the dinosaurs who ruled the world for millions of years but were helpless to the onslaught of rampant volcanic activity that happened 65 million years ago and the coup de grace of the Chicxulub asteroid strike in Yucatan.

There are several levels of life form ending threats out there in the universe.

Some of them coming from Earth itself, Earthquakes, floods, volcanoes, hurricanes, tornadoes and the like.

Then from space, comet hits like the Tunguska explosion of 1908. If that had hit ANY major city on Earth, goodbye city. Of course that is not a lifeform threat but the Chicxulub came close and if it happened today there would not be enough of humanity left to have a civilization.

So just getting colonies on the moon would be enough, well, viable colonies not dependent on earthy supplies, but a real independent colony, pretty much no matter what happens to Earth, humanity can survive.

Then there is the interstellar threat, IE, supernova blasts.

If you are within 5000 light years of one of THOSE babies, your planet will be ruined for such things as humans.

A supernova packs as much energy in its explosion as what is normally going on in the rest of the galaxy.

All the pent up energy inherent in atoms blasting off at once equals the output of energy for the entire galaxy, at least for the time the explosion lasts.

That alone is mind boggling to me, but the effects on biospheres within 5000 light years is devastating, you kiss the Ozone layer goodbye on day one, then there is no protective layer to stop ultraviolet radiation from hitting the ground and there goes all your plant life. No plant life, no herbivores, no herbivores, no predators. The cycle of life comes to a dead stop. Back to bugs and such. Humanity might, MIGHT, survive such a catastrophe living in underground caverns powered by nuclear energy and such, I am sure the sci fi guys have written such stories but it would have to have been started centuries before such an incident, with seed depositories, animals, a literal ark underground. Of course there is no such preparation since the last supernova was like in 1600 or thereabouts and that one was far enough away to be survivable but it was the brightest star in the sky for weeks.

A closer one would be deadly.

So a colony on the moon would maybe survive such a strike since there is no atmosphere and everyone would be underground for the most part anyway.

So having safe havens off Earth can make humans the survivors of such catastrophes but only if we prepare decades in advance.

If we don't, we just prove how stupid humans were and didn't deserve to survive.

If we do, we might be around a million years from now. Pretty simple when you think about it.

Originally posted by sonhouse
True enough! It won't be evolution applications that will get us off this nice nest of a planet into space where the human race might survive a world wrecking catastrophe, a step up from the dinosaurs who ruled the world for millions of years but were helpless to the onslaught of rampant volcanic activity that happened 65 million years ago and the coup de g ...[text shortened]...

If we do, we might be around a million years from now. Pretty simple when you think about it.

Hang on, you need to update your numbers.

Supernovas are not a threat at anything like 5000ly.

As I pointed out in the supernova thread its more like 50~100ly.

YouTube

Live NASA google hangout streaming from 18:00 UTC

(ie live now, just strated)
Phill plait on for an hour from 18.50 UTC

http://www.slate.com/blogs/bad_astronomy.html

Well, it went out in a puff of smoke, so I guess that's the end of this thread.

Originally posted by googlefudge
Hang on, you need to update your numbers.

Supernovas are not a threat at anything like 5000ly.

As I pointed out in the supernova thread its more like 50~100ly.

This 'bad astronomy' site talks about bad effect that can happen up to 3000 ly out:

http://www.badastronomy.com/mad/1996/sn.html

Originally posted by Soothfast
Well, it went out in a puff of smoke, so I guess that's the end of this thread.

nO.... It came out the other side... but apparently tailess...

Originally posted by mikelom
nO.... It came out the other side... but apparently tailess...

Today's APOD shows a bit of it left. Time will tell if the tailings will become visible on Earth:

http://apod.nasa.gov/apod/ap131129.html

Originally posted by sonhouse
Today's APOD shows a bit of it left. Time will tell if the tailings will become visible on Earth:

http://apod.nasa.gov/apod/ap131129.html

One million kilometers is a close approach indeed. They must have known its trajectory and anticipated this might happen.

Still it is interesting as I don't think we've observed a similar comet flyby this close to the sun. Besides impacts, of course.

Originally posted by mikelom
nO.... It came out the other side... but apparently tailess...

Well, I'd expect some rocky detritus to swing 'round Sol's girdle, but little in the way of volatiles that give comets their tails can be expected to have survived if the comet did indeed fragment.

Originally posted by sonhouse
This 'bad astronomy' site talks about bad effect that can happen up to 3000 ly out:

http://www.badastronomy.com/mad/1996/sn.html

Hmmm... However if supernova were significantly harmful at 3kLy then we wouldn't be here.

There is a supernova in a Milky-Way sized galaxy every 100 years (appx, on average).

The Milky-Way is Appx 100,000 ly across.

It's thickness is on average 1000 LY. which means that it's not going to make a huge difference
where in the hight of the disk the supernova goes off.

And if we also assume that stars are spread evenly over the disk, and supernovas go off
randomly throughout the disk...

Then as a first order approximation we can model the fraction of stars in the blast radius
as As/Ag (Area Supernova/Area Galaxy) = (Pi*Rs^2)/(Pi*Rg^2) where Rs=3,000 and Rg=100,000

This fraction works out as 0.0009.

Thus the probability of any star being inside this dangerous blast radius would be 0.0009.

The probability of not being hit by any given supernova would thus be 1-0.0009

For n supernovas that becomes (1-0.0009)^n

For n=10,000 the probability of not being hit by a supernova is appx 0.01.

Thus we can set an optimistic period between any solar system being hit by a damaging supernova
of 100n which = 1 million years.

As we do not see a major mass extinction caused by a supernova every 1million years in
the fossil record we can be confident that the radius for supernova damage must be significantly
less than 3000 ly. Even from this very rough and ready first order approximation.


I would also add that The article you linked was from 1996 and Phill has done a lot more
research on the topic (and more is known) since then, and the present day articles I linked
to. (He's since written a book on the subject of threats from space, including supernova...
Which I might well have on my Christmas list this year)

Originally posted by googlefudge
Hmmm... However if supernova were significantly harmful at 3kLy then we wouldn't be here.

There is a supernova in a Milky-Way sized galaxy every 100 years (appx, on average).

The Milky-Way is Appx 100,000 ly across.

It's thickness is on average 1000 LY. which means that it's not going to make a huge difference
where in the hight of the disk th ...[text shortened]... ats from space, including supernova...
Which I might well have on my Christmas list this year)

There is some evidence of just such a mass extinction caused by a supernova. It's just they are a lot less prevalent at any given time, you have to look at a lot of galaxies to find one in our lifetimes, or at least in a very long time.

In this piece they call for a supernova to have caused a lesser mass extinction about 2 million years ago:

http://en.wikipedia.org/wiki/Extinction_event

Originally posted by sonhouse
There is some evidence of just such a mass extinction caused by a supernova. It's just they are a lot less prevalent at any given time, you have to look at a lot of galaxies to find one in our lifetimes, or at least in a very long time.

In this piece they call for a supernova to have caused a lesser mass extinction about 2 million years ago:

http://en.wikipedia.org/wiki/Extinction_event

A gamma ray burst (hypernova) is a lot rarer, and produces thin jets of radiation that
project damage to much greater distances.

And yes there are hypothesis that say that some past extinctions might have been caused by them.


However I was not arguing that supernovas (or hypernovas) are not dangerous.

I was arguing that they can't be that dangerous at such ranges because life (and us) would have
been wiped out all ready.

Statistically it can't be that supernovas are that damaging that far out, because if they were we
would have an expectation that we would have been hit by damaging radiation from over 100
supernovas just since the extinction of the dinosaurs. (remember I assumed we got hit by a supernova
once the odds of not being hit reached 1%, in reality we would expect to be hit more often than
that using my numbers)


Given that we don't have convincing evidence to regard extinction by supernova as anything other than
a hypothesis for a few extinctions that all have much more probable causes....



If you really want to look at this, then have a look at the actual energy outputs for different types of
radiation from supernova, and then do inverse square law calculations.

Originally posted by googlefudge
There is a supernova in a Milky-Way sized galaxy every 100 years (appx, on average).

I believe supernovas come in different types. Do you have the frequencies for the different types as some appear to be more dangerous than others?

Originally posted by twhitehead
I believe supernovas come in different types. Do you have the frequencies for the different types as some appear to be more dangerous than others?

Not without doing some serious research into it...

However I do know that the dangerous aspect of the gamma-ray bursts (GRB) is that
they are narrow beams of damaging radiation. And are produced by particularly
large and rarer supernova.


And the fact that the damage is done along narrow beams means that the likelihood
of being hit by one goes down considerably even before you allow for them to be much
rarer.

http://en.wikipedia.org/wiki/Near-Earth_supernova

This wiki page discusses near earth supernova, and the distances they talk about are
(in astronomical terms) quite low.

And GRB's are supposed to hit us on average 2 ish times per billion years, which fits with one
candidate for a possible GRB extinction event in the 1/2 a billion years since the formation
of complex life.