Comet Triggered Mini Ice Age?
Comets are believed by some experts to have wiped out megafauna species at the end of the last Ice Age
A sudden plunge of global temperatures 12,900 years ago at the dawn of human civilisation may have been caused by a comet impact, a British researcher argues.
Known as 'the Younger Dryas', it has been also called the Big Freeze and the Last Blast of the Ice Age - but for researchers trying to understand the Earth's ancient climate, it's one of the big mysteries of the field.
Around 12,900 years ago, Earth was on a steadily warming trend after almost 100,000 years of harsh glaciation, during which ice sheets placed a swathe of the northern hemisphere under a dead hand, extending their thrall as far as south as New England and Wales.
Unexpected plunge in temperature
But just as the glaciers were beginning to retreat, and an easier life at last beckoned for Earth's tiny population of humans, everything went into reverse.
Temperatures fell dramatically by up to 8˚C, heralding a cruel winter that would last 1,300 years. But what caused it?
Crunching powerful equations and weighing fresh evidence, an astrobiologist in Britain is pointing the finger at an unusual culprit.
Massive comet
Earth collided with debris from a vast comet, measuring 50 to 100 km across, that had wandered into the inner Solar System some 30,000 years ago before breaking up, says Bill Napier, a professor at Cardiff University's Astrobiology Centre.
The impact unleashed a firestorm that blanketed the atmosphere with ash and dust, reducing heat and light from the Sun, Napier suggests in Monthly Notices, a journal of the Royal Astronomical Society.
What is worrying, adds Napier, is that our planet still crosses the path of the remaining orbiting cometary rubble, a well-observed, although still enigmatic, phenomenon called the Taurid Complex. Many of these fragments are tiny and their burnup in the atmosphere, causing periodic showers of meteors.
Near-Earth objects
Other pieces, though, may not be so enchanting. They are not big enough to inflict global extinctions like the event 65 million years ago that wiped out the dinosaurs, but they could still devastate entire regions.
"It [the Taurid Complex] includes at least 19 of the brightest near-Earth objects," says Napier.
"Sub-kilometre bodies [objects measuring 1,000 [metres] across or less in meteor streams may present the greatest regional impact hazard on timescales of human concern."
by Richard Ingham
From http://www.cosmosmagazine.com/news/3382/did-a-comet-trigger-a-mini-ice-age
Mini-Ice Age debate rocking geology world
The normally peaceable world of geology is currently alive with a fiery debate over the theory that deadly space rocks slammed into Northern Canada about 13,000 years ago, triggering a mini-Ice Age and the eventual extinction of the woolly mammoth and a host of other prehistoric species.
That contentious hypothesis - which has prompted a number of studies in recent years probing sites throughout North America for traces of the alleged extraterrestrial blast -is under renewed attack after a team of U.S. and British researchers published a paper last week arguing that previous claims of impact evidence are demonstrably mistaken.
The new study takes particular aim at several supposed discoveries of "nanodiamonds" at sites around North America -hailed by advocates of the impact theory as proof that a cosmic blast sent showers of "shocked" rock particles across the continent 13,000 years ago.
"The usefulness of cubic nanodiamonds as impact markers in sediments remains unclear because processes other than impact might account for them," argues the new study led by Tyrone Daulton, a physicist at Washington University in St. Louis, and published in the latest Proceedings of the National Academy of Sciences.
The study also contends that the "nanodiamonds" documented in previous studies were, in fact, misidentified samples of a carbon-based substance called graphene that does not provide proof of a meteorite strike. But one of the researchers whose findings are targeted in the study -University of Oregon scientist Douglas Kennett -has shot back at Daulton, calling his work "fundamentally flawed science" that is unfairly discounting the impact hypothesis.
Woolly mammoths are one of several species of megafauna that some scientists believe became extinct following a comet-induced mini-Ice Age.
The controversy is focused on a thin rock layer seen around the world that represents the boundary of the Younger Dryas -a well-documented, 1,000-year period in Earth's history, characterized by a sudden plunge in global temperatures beginning about 13,000 years ago.
The Younger Dryas cold spell roughly coincides with the arrival of humans in North America and with the precipitous decline and eventual disappearance of populations of mammoths, mastodons, sabre-tooth tigers, Ice Age horses and other creatures that once roamed the continent.
Some scientists have attributed the Younger Dryas deep-freeze and the subsequent string of megafauna extinctions to climate change caused by a massive meltwater outburst into the Atlantic Ocean -probably near present-day Hudson Bay - as Ice Age glaciers retreated north.
Others have blamed the abrupt loss of so many mammal species on over-hunting by early big-game hunters whose tribes had recently migrated to North America from Siberia.
About five years ago, studies began proposing the idea that a comet or asteroid might have struck a glacial ice dam near Hudson Bay, causing an initial catastrophe for North American ecosystems and then kick-starting long-term, global climate changes that wiped out the mammoths and their contemporaries.
Last year, several U.S. scientists headed by Kennett, unearthed a layer of what they called "nanodiamonds" on a California island, a find described at the time as "smoking-gun" proof that a massive comet triggered the Younger Dryas, killed off the mammoths and threatened the fragile foothold of North America's earliest human inhabitants.
But Daulton says his team's study disproves the theory because it shows that no nanodiamonds have been accurately linked to any of the North American sites.
© Copyright (c) The Montreal Gazette
Radioactive "Green Layer" at Ice Age site in Mexico
Investigation of Sediment Containing Evidence of the Younger Dryas Boundary (YPB) Impact Event, El Carrizal, Baja California Sur, Mexico
The YDB extraterrestrial impact hypothesis posits that one or more extraterrestrial objects exploded over the Laurentide Ice Sheet 12,900 ± 100 years ago. This event is purported to have triggered the Younger Dryas stadial and coincides with the Rancholabrean termination and disappearance of the Paleoindian Clovis culture. Evidence supporting or refuting this hypothesis has great implications for the fields of geology, paleontology, and archaeology.
Geochemical markers of the YDB impact (Firestone, et al., 2007) include magnetic and carbonaceous spheroids, elevated levels of radioactivity and iridium, and nanodiamonds (lonsdaleite). The event horizon at sites across North America is often overlain by a darker layer (the “black mat”).
Our field site for testing the YDB ET impact hypothesis is located on the El Carrizal fault, 38 km south of La Paz, Baja California Sur, Mexico, at 23°46’34.9″ N, 110°18’41.0″ W. The site is situated along the uplifted (SW) side of the fault within an arroyo exposing Pleistocene-Holocene transition sediments. The presence of in situ Rancholabrean megafauna fossils at El Carrizal was independently verified by investigators from Universidad Autonoma de Baja California Sur, La Paz; cranial and postcranial sections of Mammuthus columbi were excavated from the sampling site in 1997. Sediment samples were taken from a 3 m stratigraphic section at El Carrizal which spanned the sediments where the mammoth fossils were located. This section included an anomalous greenish clastic layer at approximately 138 ± 6 cm below road surface; this layer suggests a correlation to the “black mat” stratum noted at many other terminal sites.
Preliminary laboratory analysis yielded magnetic spherical particles under 60-70x magnification, and a peak in radioactivity was found at a depth of 136-138 cm, coinciding with the lower part of the darker green layer. Elemental analyses for iridium and lonsdaleite are currently underway.
If conclusive evidence of an extraterrestrial impact is found at El Carrizal, it will be the most distal documented evidence to date. This will significantly extend the geographic range of effects for the impact event.
- SCRUGGS, Melissa A., RAAB, L. Mark, MUROWCHICK, James, STONE, Matthew W., and NIEMI, Tina M., Geosciences, University of Missouri – Kansas City, 5100 Rockhill Road, Room 420 Flarsheim Hall, Kansas City, MO 64110, mas6gc@mail.umkc.edu
From http://cosmictusk.com/geology-conference-independents-locate-anomalous-green-layer-at-ydb-with-spherules-in-mexico
Images http://www.cosmosmagazine.com/files/imagecache/news/files/news/20100405_chesapeake-impact.jpg
http://cdn.wn.com/ph/img/de/7d/fc6bfe6ac359705afc2ee6a652d0-grande.jpg
http://nationalityinworldhistory.net/images/comet_earth.jpg -
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