December 12, 2017

13.04.10- Mammoth Extinction vs. Impact Theory.

An Ice Age extinction mystery has just got more complicated. North America used to be home to some amazing mega-animal life, including wooly mammoths, saber-toothed cats the size of grizzly bears, and armadillos the size of Volkswagens. Then, around the time period known as the Younger Dryas about 12,900 years ago, a mass continent-wide extinction event occurred. Key theories include massive climate change, a large cometary impact, and that greatest of all predators, man. Now, research by Jacuelyn Gill of the University of Wisconsin has dealt a blow (pun intended) to the cometary impact hypothesis. Key evidence for a large airburst over the Laurentide ice sheet comes in the form of an iridium layer seen in the sedimentary deposits laid down at the time, as well as the discovery of minuscule nano-diamonds generated by the heat and blast of the explosion. The problem is, Gill’s studies of fungus spores found in fossilized dung finds the extinction event was already underway well before the impact, around 14,000 years ago. In addition, a mastodon skeleton in the Cincinnati museum has been found to have been dated from circa 10,055 years ago, well after the impact! This seems to put the appearance of Clovis man and overhunting as the key to large mammal extinction in the Ice Age North American scene. Perhaps even a combination of the factors was the cause. The concept of the Early Dryas extinction is unique because it is the most recent extinction event (other than the one we’re currently undergoing!) along a timeline of multiple events throughout the history of life on Earth. Being the most recent, perhaps more evidence for complicating factors is simply lying around for us to find. This debate is thus the hottest topic of all large extinction events. And one has to wonder; what would life in modern U.S. suburbia and camping trips be like if there were still saber-toothed cats around?

08.11.09:Does Cometary Mass Extinction Need to be Rewritten?

Comets are cause all mass extinctions in Earth’s history, right? Maybe not, if new research is correct. Simulations run by the scientists at the University of Washington now suggest that the giant planets of Jupiter and Saturn may do a much more through job of cleaning up incoming debris than is generally realized. Short period comets such as Halley’s are generally accepted to be denizens of the Kuiper belt, which extends out to 100 Astronomical Units (A.U.s), while much more numerous populations of long period comets are theorized to come from the Oort cloud, a massive solar system-engulfing sphere at a distance of 1,000 A.U. to up to 3 light years distant. Traditional cometary mass extinction theory states that when a star passes close enough to the shell of the Oort cloud, a rain of comets are pried free and the inner solar system becomes a celestial shooting gallery for a million years or so. Simulations, however, suggest no more than three impacts could have occurred over the last 500 million years or so, fuel for at best maybe a minor extinction event or two. Then there’s the pesky affair of some extinct species shown to exist above the K-T iridium layer… doubtless, the case of mass extinction is a thoroughly messy business. As reported earlier last month in this space, more than one impactor is suspected in the extinction of the dinosaurs. Examination of other inner solar system bodies should pin down the frequency, duration, and average number of killer comets, as the Moon, Mars and even Mercury have relatively little erosion and would be potential targets as well. Any incoming comet stands a 40% chance of having its orbit altered by Jupiter, as happened to Hale-Bopp in the late 90′s. Thanks, Jove!

 

 

 

AstroEvent of the Week: February 2nd-8th, 2009; Spot a Daytime Venus!

A Daytime Venus Shortly After Occultation. (Video by Author).

 

Astronomy isn’t just restricted to a night time activity. Many folks do not realize that objects such as the Moon can be spotted even in broad daylight. This week, I give you a fun daytime naked eye challenge; spotting Venus in the daytime.  No special equipment is required; just a sharp set of eyes and persistence. [Read more...]