Monday, April 06, 2009

Ordovician Extinction Caused by Gamma Ray Burst?

A new study has suggested that a brilliant burst of gamma rays may have caused a mass extinction event on Earth 440 million years ago, and a similar celestial catastrophe could happen again in the future.

Most gamma-ray bursts are thought to be streams of high-energy radiation produced when the core of a very massive star collapses. According to a report in National Geographic News, the new computer model shows that a gamma-ray burst aimed at Earth could deplete the ozone layer, cause acid rain, and initiate a round of global cooling from as far as 6,500 light-years away.

Such a disaster may have been responsible for the mass die-off of 70 percent of the marine creatures that thrived during the Ordovician period (488 to 443 million years ago), suggests study leader Brian Thomas, an astrophysicist at Washburn University in Kansas.

The simulation also shows that a significant gamma-ray burst is likely to go off within range of Earth every billion years or so, although the stream of radiation would have to be lined up just right to affect the planet.

Currently WR104, a massive star 8,000 light-years away in the constellation Sagittarius, is in position to be a potential threat, according to Thomas.

Study author Thomas’ former graduate advisor, Adrian Melott, first proposed in 2004 that a gamma-ray burst near Earth wiped out Ordovician life.

Since then, both researchers have been tackling pieces of the puzzle.

According to their newest models, gamma radiation from a nearby burst would quickly deplete much of Earth’s protective ozone layer, allowing increased ultraviolet radiation (UV) from the sun to reach the surface.

In the longer term, chemical reactions in the atmosphere would produce dark, nitrogen-based gases that would block the sun’s heat and trigger global cooling, even as the gamma rays continued to deplete ozone and let in UV rays, the authors suggested.

Some of the pollution would fall as damaging acid rain, which can severely disrupt ecosystems.

From what I can see here, this looks like its just a sim. Do they have any field work to support their assertion? Anyone have this paper? Or is it even a paper at all?


Neil said...

Melott and Thomas have been pushing this story for a while. Unfortunately, or fortunately depending on your perspective I suppose, a gamma ray burst would theoretically leave nothing in the way of physical or chemical evidence that it occurred. The latest line of argument is that the latitudinal gradient of extinction in the Ordovician is consistent with a gamma ray burst centered somewhere over the Southern Hemisphere. Apparently the paper is in review, however a pre-review copy can be found here:,%20Brian%20Late%20Ordovician.pdf

Will Baird said...

I already got a copy from Dr Brian. I'll be reading it probably tomorrow. I'll see how it states the evidence.

There has to be some more evidence that they can offer up than just the pattern of the extinction. If there was an intense enough GRB then there ought to have been some sort of signature in the isotopes.


One comment I saw back wrt Permian Extinction was that there was a lot of 'mutation' in evidence from the fossils at the end Permian event. This has been attributed to the UV layer getting mopped by the H2S. IF there was a GRB that took out the ozone layer, there ought to be the same 'sort' of very high variation then. Additionally, there should be no evidence of H2S or other chemicals being present.

Furthermore, the Ordo Dying ought to be top to bottom ought to be testable with a GRB just based on the taxa that go extinct: it's perfectly measurable to figure out the shielding based on the depth in water or crustal coverage.

"yknow what, I'll see if I can talk to some labbies here about whether or not a GRB would leave chemical or physical traces. Not sure I would expect it to not leave anything.

This hypothesis needs more meat, I'd say.

Neil said...

It's telling I think that thus far we only really have consensus on causality for one major mass extinction, KT, and even that one is still debated. I suppose the PETM/clathrate story is pretty solid now. Clearly in the Permian there is substantial multi-causality/synergism/feedback going on and I suspect that's probably true for the others as well, including KT.

Melott and Thomas themselves claim that GRB would leave know long-lived isotopic evidence: any chemical by-products would decay in 1 million years or so.

You're certainly right that testing the extinction pattern in terms of depth ought to testable, except that the life-mode (e.g. preferred water depth) for so many Paleozoic (and Mesozoic for that matter) taxa remains controversial.

The evidence for mutagenesis in the Permian comes from land plants of which there weren't a whole lot in the Ordovician...not to say you couldn't pick up some kind of evidence for pervasive mutation. However, if it only affected 1 or 2 generations as I would suspect for a GRB, you would have to be exceptionally lucky.

Will Baird said...

I think the KT is sown up. There are dissenters, but they are very, very much the minority. My KT post is done...I'm just considering whether I did some math boo-boos.

The Eocene/PETM seems pretty straight forward.

The Permian Extinction was almost the kitchen sink, but not really. Causality and the resultant chain reaction seem like they are being fleshed out pretty well though. I think that the impact story is dead though no matter what.

The Ordovician didn't seem very controversial among what I've read so far. I'll need to hunt down those physicists: i have a hard time believing that something that womps the whole planet would leave no significant isotopic signature.

Are there good surface algae fossils? Or how about algae reef builders? Were they present at the time? Shallow water taxa are what we are looking for mostly.

I'll be reading during lunch.

Neil said...

I would say that the Ordovician extinction has been quite the point of some arguing that it is either a statistical artifact or was simply a consequence of high provinciality coupled with average "background" extinction rates.

Our appreciation of the early fossil record of land plants has been growing (no pun intended) by leaps and bounds lately so perhaps there is some hope there. There is some suggestion of a post Ordovician extinction resurgence of microbial reefs, akin to what happened in the Early Triassic, but this would presumably post-date any spike in cellular mutation. For that matter, microbial textures are notoriously difficult to interpret (as far as the environmental vs. biological factors which control them) so detecting mutation in microbialites would likely be exceptionally difficult.

Okay, back to abstract writing! Yikes