Thanks for the interesting description of a large impact event over water. You raise some interesting questions (large increase in ice accumulation and etc.). Certainly you're talking some extinction level event.
There is a theory out there concerning an impact in Argentina over 3M years ago that wiped out some South American species as being the last major impact, and most know about the big one North of the Yucatan that is attributed to the demise of the dinos, 65M years ago.
Likewise, really large volcano eruptions have been attributed to major losses of flora and fauna. A few came close to wiping out Homo sapiens if you can trust the work of certain researchers.
Evidence seems to support large impacts occurring over millions of years while major volcanic eruptions occur over thousands or hundreds of thousands of years. Take another look at the ice core data chart. As far as I know, the science behind its accuracy is pretty solid (please direct me to evidence otherwise).
Looking at only the last 400K years, it’s hard to miss the four unusual periods of VERY short term warming (relatively) before temperatures fall again. The odds are good that some sort of cyclical phenomenon is causing this warming. IMO, either the sun through increased output, or heat pulses from the earth’s interior (warming oceans) are the likely candidates. I don’t see how an impact would cause a warming period; much less not leave recent evidence behind, since we’re at the end of the current 12K year warm period.
“The science behind its accuracy” is the assumption that nothing has happened out of the ordinary, and that there are therefore definitive layering patterns representing individual years. In the case of the Eltanin impact (that may be what you referred to as the Argentinian impact 3M years ago, it was actually about 2M years ago, and offshore in the Pacific) laid down an iridium signal found in the ocean bed cores.
https://www.google.com/search?q=eltanin+impact+iridium
http://www.freerepublic.com/focus/bloggers/1248414/posts
The problem with *any* gradualist model for massive glaciation (the ice ages iow) is that those assume that cold will make it work, but don’t have any mechanism by which the Earth can stay cold enough that snow won’t melt but with warm enough waters that the hydrologic cycle will continue to contribute snow accumulation. This problem is why there is so much disagreement among the gradualists as to how it happened, and why the basic consensus doesn’t work, merely restates the lowest common gradualist view — that glaciation happened gradually.
My problem with CO2 and Antarctic cores is twofold — number one, despite the “lag” between higher temperatures as inferred from proxy data and the later increase in CO2 (ditto), the Antarctic core data is pointed to by the AGW propagandists (including those formerly allowed to operate on FR) as evidence that CO2 causes warming, IOW, that the studies themselves only came about due to the political seduction of the sciences; and number two, again, that they operate under the assumption that there’s been no sudden deposition of ice.
Since the conclusion is completely founded on the assumption, the conclusion can’t be pointed to as evidence of the assumption.
Iridium in the seabed means iridium may have been deposited in the lower layers of the Antarctic ice. If someone drills a 3M year core, with the dating of the core based on the gradualist assumption, they probably won’t find any iridium. Since most of the icecap was laid down at one time (or possibly in several widely spaced episodes; again, the Sun doesn’t have much time to melt miles of ice in the Antarctic, but the N Pole ice is thinner, afloat on the ocean, and melts every year in the 24 hour days of summer), the iridium concentration should be greatest near the foundation, although it could also be spread out through the entire layer that was laid down over a short interval.
Since the evidence (see the link to the FR topic for more links and info) is that Antarctica was temperate less than 3M years ago, the ice cap there can’t be 30 million years old — that 30M year figure is of course based on the continental drift model, rather than actual data from Antarctica.
Thanks again, Errant!