Nearby Supernova Causes Mass Extinction?

hcg50a writes "AP has a story on Yahoo about a theory that a blast of gamma rays from a distant supernova destroyed the earth's ozone layer, allowing normally shielded intense UV radiation from the sun to kill life on earth. The second-largest extinction in the Earth's history, the killing of two-thirds of all species, may have been caused by ultraviolet radiation from the sun after gamma rays destroyed the Earth's ozone layer. Astronomers are proposing that a supernova exploded within 10,000 light years of the Earth, destroying the chemistry of the atmosphere and allowing the sun's ultraviolet rays to cook fragile, unprotected life forms."

Comments

Mars?

[MobyDisk]

Could this also have affected life on Mars, but it never recovered?

(Rhetorical question - we can't really know)

Re:Mars?

[misterpies]

The planet has reached a natural balance. The climate is stable. It's just very hot. The atmosphere is composed of heavier molecules than here on earth -- mostly CO2 -- so it can withstand much higher temperatures before being boiled off.

Why? Atmospheres "boil away" when the molecules in the atmosphere are moving faster than the escape velocity of the planet. But while particles in a hot gases move faster than those in cooler sample fo the same gas, gases made up of heavy and/or complex molecules will have lower particle speeds than gases made of light, simple molecules at the same temperature.

This is because temperature is related to energy: for two gases to have the same temperature means that the average energy of each particle is the same in the two gases. But heavy molecules reach the same kinetic energy at a lower speed (a molecule four times the weight reaches the same kinetic energy at only twice the speed). And just as importantly, complex molecules can store more energy in "internal modes" -- by spinning and vibrating. N2 and O2, the main constituents of earth's atmosphere, both have 1 vibrational and 2 rotational modes. CO2 is heavier, and has 3 vibrational and 3 rotational modes.

As a result, Venus's CO2-dominated atmosphere can be be much, much hotter before boiling off compared with earth's atmosphere. Probably the reason Venus's atmosphere is dominated by heavy elements and complex molecules is that the lighter stuff has already escaped.

Silly Dinosaurs...

[JavaLord]

They should have been using sun-bloc SPF-10,000,000

Of course

[aridhol]

A supernova that's really nearby (such as our own sun) could put a huge damper on things, as far as life is concerned.

Re:Of course

[Pembers]

IANAP, but as I understand it, our own sun is too small to go supernova.

Re:Of course

[Anonymous Coward]

You're right. Our sun is a dwarf star. It's death will be marked by expansion into a giant red star, then compression into a small core of oxygen and carbon, and finally lights out. Check out the BBC's page on the death of stars.

Wow.

[NegativeK]

I'm not sure if other hard-sci-fi authors have addressed this, but Stephen Baxter's Manifold Space used a theory like this to address the Fermi Paradox: if we assume that physical laws are constant throughout the universe, why hasn't there been contact with other species? His answer? A sort of galactic reset.. When conditions are just right, two neutron stars (or other heavy bodies) will enter a decaying orbit, and release gravitational energy in the form of gamma rays (I believe.) In short, resetting the biological clock of our galaxy. Different from destroying the ozone layer, but this article makes it seem a little less far fetched, doesn't it?

Re:Wow.

[Baron_Yam]

It appears that there are several factors for creating a 'potential life zone' in the galaxy.

Given our sample of one known case, we assume you need a Sun-like star, with an Earth-like planet in an Earth-like orbit, probably with an Earth-like moon. You also need outer gas giants to reduce the inbound crap that would otherwise beat the hell out of us. That's just the local stuff.

You also need to have a solar system that won't pass through a dangerous region of space while life is trying to evolve... that means no 'stellar nurseries' nearby, or anything likely to go 'boom' in a big way.

In other words, even if there are very large numbers of potentially Earth-like planets, with conditions nearly exactly like the ones we're familiar with, they might indeed be sterilized frequently enough to prevent life from ever getting anywhere - and maybe even one sterilization could render a rock permanently hostile to life.

Still, mankind knows relatively little about the galaxy and the probabilities of the many factors we suspect are related to the chance of life getting started, never mind developing life with a penchant for coming to visit us and mutilate our cows and cornfields while rectally probing drunken hicks.

Re:Wow.

[hcg50a]

Good point.

The biggest problem with the Drake Equation is that it it way too simplistic. In our galaxy, there is definitely a habitable zone which the solar system is in. If it were much closer to the center of the galaxy, there would be too many events like energetic supernovae that would kill all life on the earth. If it were much farther away from the center, there would not be enough heavy elements to form earth-like planets.

Life is fragile and cannot tolerate too many nearby energetic events.

Life similar to Earth's probably exists elsewhere in our galaxy, but may not be very common.

Re:Wow.

[AuraSeer]

It has nothing to do with "approach vectors." Large objects don't usually fall in from outside the solar system.

The problem is leftover crumbs of planetary formation-- asteroids, planetesimals, the assorted random junk that has been circling the sun as long as the Earth has. In our system, Jupiter had the effect of removing that junk from our vicinity. It consumed a lot of rocks, and flung others out of the system by the slingshot effect. The remaining ones got shepherded into their own fairly circular orbits, in what we call the asteroid belt.

Without Jupiter (and the other giants), there would be lots more big rocks flying around the place. They also wouldn't be confined to the asteroid belt; they'd be zooming all over the place, and crossing over other planets' orbits. Those crossovers are what make a rock likely to hit a planet and cause extinctions.

Jupiter is not like a linebacker who jumps in front of asteroids for us. It's more like a maid, who swept the system clean a long time ago and made sure we wouldn't trip over anything.

Our aversion to going outside...

[NanoGator]

... has saved us!

reported on in 2003

[MonkeyBoyo]

In 2003 this story was reported in nature.

And here the link to the pre print.

The secret of the missing evidence

[Baron_Yam]

is in the article.

The galaxy has completed two rotations since the event, and given that the various components of the galaxy don't rotate perfectly synchronously, the remenant nebula is either not where you'd expect, or smeared out of all recognition.

No Real Evidence yet...

[Slick_Snake]

"We think there is very good circumstantial evidence for a gamma ray burst."

The article clearly states that they have no real evidence to speak of. The only thing they do have is the ice age that occured at the time of the extintion. They admit that no traces of a supernova near earth can be found, and blame it on the rotation of the Milky way.

Melott said there is no known evidence of such a nearby supernova, but that in 440 million years the Milky Way would have rotated almost twice and traces of the explosion could have been moved during that time.

I will give them that it is a possibility, but until they have some more convencing evidence I'm not ready to jump aboard.

Re:No Real Evidence yet...

[dexter riley]

Agreed, the article didn't describe hard evidence that the Earth was the target of a gamma ray burst 440 million years ago. Does anyone know where you would look for such evidence? Would there be a detectable chemical signature in soil sediments from this period? Or is this something you would need to look at moon rocks or cometary ices to find some evidence of the gamma rays?

Evolution?

[dnahelix]

Could it also be a factor in Evolution?
Increased exposure to radiation causing a period of increased mutations in the surviving species?

Re: Evolution?

[Black Parrot]

> Could it also be a factor in Evolution? Increased exposure to radiation causing a period of increased mutations in the surviving species?

The opportunities for species to radiate into vacated niches would probably have a much bigger evolutionary impact than the effects of a short-term boost in mutation rates.

Re:Where's the remains?

[squiggleslash]

Not necessarily. This happened 440 million years ago, it's quite conceivable that the system has moved massively in relation to us since then. (It was "only" 10,000 light years away as it was.)

Where's the Ka-Boom!?!?

[damien_kane]

There was supposed to be an earth-shattering Ka-Boom!!!

the next big one primed & feisty

[iggymanz]

and here's the ticking time bomb within 10,000 lightyears that's going to finish us off. It may in fact already have supernovaed, and the gamma ray clam-bake coming at lightspeed! Oh, and recently revised estimates indicate no more than 20,000 years to the big pop. This will mess up your hard disk.

Re:the next big one primed & feisty

[Kris_J]

God, no, not my hard disk. That's where I keep all my stuff.

Re:Protection from the other side of the Earth.

[iggymanz]

I used to work at Fermilab, and the graphs I've seen of gamma ray bursts attributed to supernovae cover a period of tens or hundreds of seconds, with a several second huge peak, something like this

As someone else has already pointed out, this moves at lightspeed, so there's no warning. You do realize there's not enough jets/planes to even hold 0.00001 of humanity, and the real problem would be trying to outrun our own daytime as the earth is baked by our own sun. You think people will wait nicely in line for a plane on a first-come first-serve basis? Hah, imagine your local airport looking like the most violent moments of the worst civil war. Cheers!