Friday, March 10, 2006

Extinctions revisited But not human-caused ones:
Mass extinctions – a threat from outer space or our own planet's detox?

Earth history has been punctuated by several mass extinctions rapidly wiping out nearly all life forms on our planet. What causes these catastrophic events? Are they really due to meteorite impacts? Current research suggests that the cause may come from within our own planet – the eruption of vast amounts of lava that brings a cocktail of gases from deep inside the Earth and vents them into the atmosphere.

. . .

"There is scant evidence of impacts at the time of other major extinctions e.g., at the end of the Permian, 250 million years ago, and at the end of the Triassic, 200 million years ago. The evidence that has been found does not seem large enough to have triggered an extinction at these times."

Flood basalt eruptions are – he says - an alternative kill mechanism. These do correspond with all main mass extinctions, within error of the techniques used to determine the age of the volcanism. Furthermore, they may have released enough greenhouse gases (SO2 and CO2) to dramatically change the climate. The largest flood basalts on Earth (Siberian Traps and Deccan Traps) coincide with the largest extinctions (end-Permian, and end-Cretaceous). "Pure coincidence?", ask Saunders and Reichow.

I've posted about this a couple of times, that there are a few researchers (probably more than a few) who have bucked the trend of assuming the K-T extinction event has been solved conclusively by the impact theory. It's a similar problem to the overkill-climate controversy in North American post-Pleistocene extinctions in that there is evidence for both but not enough -- or at least, not one definitive piece -- to nail it down either way.

Easter Island update View of Easter Island Disaster All Wrong, Researchers Say

The first settlers on Easter Island didn't arrive until 1200 AD, up to 800 years later than previously thought, a new study suggests.

The revised estimate is based on new radiocarbon dating of soil samples collected from one of oldest known sites on the island, which is in the South Pacific west of Chile.

The finding challenges the widely held notion that Easter Island's civilization experienced a sudden collapse after centuries of slow growth. If correct, the finding would mean that the island's irreversible deforestation and construction of its famous Moai statues began almost immediately after Polynesian settlers first set foot on the island.

. . .

Lipo thinks the story of Easter Island's civilization being responsible for its own demise might better reflect the psychological baggage of our own society than the archeological evidence.

"It fits our 20th century view of us as ecological monsters," Lipo said. "There's no doubt that we do terrible things ecologically, but we're passing that on to the past, which may not have actually been the case. To stick our plight onto them is unfair."

The Science article is here for those with subscriptions. It's a fuller account of the work that was posted on a while ago. I pasted those second two paragraphs because it represents an interesting quandary within archaeology and parts of society generally. The thinking has been, since probably the '60's or '70s (with roots much earlier, obviously) that aboriginal groups by and large lived in complete harmony with their environment. I think the term that's been used is something like the 'original environmentalists'. This has been changing somewhat recently with some researchers showing/arguing that aboriginal (i.e., non Western European) groups were in many ways as rapacious as modern Euro-civ has been. For example, Jack Broughton's work on overhunting in California, and Jared Diamond's book on societal collapse through ecological devastation. This idea does have earlier renditions, such as Martin's Overkill. Heck, some researchers are even arguing that early farmers were doing global warming 10,000 years ago.

Overall, this has probably been a good corrective to the Noble Savage myth that held that all the evils of the world were strictly a western European phenomenon. After all, science doesn't work well with myths even if they do make some people feel good about themselves. We need to keep in mind, however, that going overboard the other way carries its own dangers. This work shows that the situation is far more complex than those two extremes (see mass extinctions above). Easter Islanders probably didn't go rushing headlong over an ecological cliff just so they could build pretty statues, nor was it solely due to European contact. It's a good cautionary tale that one really needs to be mindful of the limits of existing data and that exciting politically-correct (of whatever pursuasion) arguments don't make up for a lack of good radiocarbon dates.