The Great Dying

[lindagarrette]

Here's an interesting new proposal to explain the extinction of most life on earth 250 million years ago. There is hope that if we kill ourselves off, the planet may regenerate with perhaps new and very different species.

In a paper published by Science Express, the online version of the journal Science, yesterday researchers headed by University of Washington scientist Peter Ward said they have found no evidence for an impact at the time of "the Great Dying" 250 million years ago.

Instead, their research indicates the culprit might have been atmospheric warming because of greenhouse gases triggered by erupting volcanoes.

The extinction occurred at the boundary between the Permian and Triassic periods at a time when all land was concentrated in a supercontinent called Pangea.

The Great Dying is considered the biggest catastrophe in the history of life on Earth, with 90 per cent of all marine life and nearly three-quarters of land-based plant and animal life going extinct.

"The marine extinction and the land extinction appear to be simultaneous, based on the geochemical evidence we found," their paper said.

"Animals and plants both on land and in the sea were dying at the same time, and apparently from the same causes too much heat and too little oxygen."

[Aquagem]

Originally Posted by lindagarrette

Here's an interesting new proposal to explain the extinction of most life on earth 250 million years ago. There is hope that if we kill ourselves off, the planet may regenerate with perhaps new and very different species.

This would make a great movie. Trapped by its instincts into overconsuming and overpopulating, a major species destabilizes the biosphere and brings the temple crashing down around it. Long after, with the diminutive remnants of its once-proud genetic pool near extinction in an impoverished ecosystem, a new dominant species gleans just enough information of the debacle to fashion it into a mythic story of a prior Golden Age brought low by a conspiracy of fated forces (or a pissed-off god, maybe). A new disaster story replaces the former one (something about a flood, I think) and becomes the basis of a new round of organic and cultural evolution by a new species. Much later, then, some obscure member of this new culture/species, deeply enmired in the waste of its own success, sits and writes a note somewhat like this one...

[Fishteacher73]

I had a proffessor that argued against meteor impact as the source of the mass extinctions. He argued that the fossil record showed a rapid loss of life (Geologically) but way to slow to be caused by a single cataclysmic event. He offered the explanation that the extinction of the dinosaurs actually coincided with the shift of plant life fron evergreen to deciduous. This would greatly disrupt the food chain and crash an ecosystem. I have not seen any other research connecrted with trhis, but he was a amart man (Asst. Dean of Science at UT). Any ideas?

[lindagarrette]

I think the meteor theory took hold because it seemed to fit at a time many scientists were looking into the potential damage to our planet if there were another impact. But there was never any substantial evidence.

[Fishteacher73]

The one missing piece in this theory is that it does not connect to the mass extinctions in aquatic life...Although a large shift in O2 producing plants could possibly alter the O2 content of the seas, triggering an ecological breakdown there. This is just speculation, as i have not seen any studies that indicate any shifts in marine chemistry at that point, nor if the shift fron year round production to seasonal production of O2 by plants would drasticly effect O2 concentrations in the atmosphere and therefore marine makle-up.

[Aquagem]

Originally Posted by lindagarrette

I think the meteor theory took hold because it seemed to fit at a time many scientists were looking into the potential damage to our planet if there were another impact. But there was never any substantial evidence.

The Great Dying is the title of an excellent book about the K-T boundary cataclysm, written by Kenneth Hsu about 1985. It may actually be his title that has given us the term we are now using to describe the end of the Paleozoic. Hsu was the lead scientist on the drilling expedition that first penetrated the K-T boundary in the Atlantic to test the hypothesis that the exinction coincided with a comet collision as predicted by Alvarez. The book is a great read, because Hsu tracks the research that came out of the first discovery of Iridium made at Gubbio, Italy and moved on to further studies documenting the global nature of the deposits. The drilling was a critical instance, because many claimed that there could be large time gaps in the known boundary areas on land, many of them having been twisted and eroded during the course of Cenezoic tectonic events.

Long story short, the drilling, fraught with difficulties, finally succeeded in getting deep enough to draw a core from the ooze, and the evidence pretty much sealed the deal. At the boundary was the expected Iridium layer, and immediately below it were perfectly healthy and flourishing Cretaceous flora and fauna, continuous with deeper strata. immediately above the boundary were several layers of evidence of major catastrophe, including the complete extinction of over 90 pct of the species found only centimeters below. Farther up the column, the microorganism counts climbed again, but the large majority were new, and the old ones never came back.

Since then, as I have read through the years, other bore holes in the Pacific, the Arctic, and other locations have also shown that the Iridium layer is truly a global artifact. As I remember, the number of drillings is now quite large.

The recognition of the Chicxulub crater as the impact point in the 90's cemented the case, not just because it was a convenient landform, but because it also pulled together geological evidence in the southern US of a major impact that had been known for decades. Take a look at the following if you have a bit of time. The first one is very visual and conveys the strength of the observations in supporting the K-T collision hypothesis.


Chicxulub and the Cretaceous Tertiary Boundary
Explores the Chicxulub impact event and the Cretaceous Tertiary mass
extinction. Understanding the KT Boundary. The KT boundary ...


www.lpl.arizona.edu/SIC/impact_cratering/ Chicxulub/Chicx_title.html - 7k - Jan 24, 2005 - Cached - Similar pages

Discovering the Crater

... It is a huge buried impact crater that is called Chicxulub, a Maya word that roughly
translates as "tail of the devil." The crater, now buried beneath a ...
www.lpl.arizona.edu/SIC/impact_cratering/ Chicxulub/Discovering_crater.html - 10k - Jan 24, 2005 - Cached - Similar pages
[ More results from www.lpl.arizona.edu ]

Based on the above, I'd say there is plenty of very good evidence for the collision at the K-T boundary. The debate over the Permo-Triassic Crisis came to prominence only after the K-T issue was resolved, and early research was unclear about the presence of Iridium in that transition.

[lindagarrette]

You are correct about the K-T period and I should not have disclaimed evidence of a meteo causing global extinctions in any case. The time period I referenced, hoever, was much earlier, pre-dinosaur, about 250 million years ago and presumably there were claims of a collision causing that catastrophy as well which may have been..