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Scientists have crunched the numbers for the September 2007 meteorite that landed in the Andes and suggest that the larger than normal impact crater resulted from the object’s unusually high speed.

Most stony objects that blaze through Earth’s atmosphere are blasted to bits by air resistance at high altitude (SN: 11/23/02, p. 323). Because the meteorite that struck eastern Peru on September 15 landed intact, its minerals must have been stronger than those typically found in similar extraterrestrial objects, says Peter Brown, an astronomer at the University of Western Ontario in London, Ontario. He and his colleagues report the first comprehensive analysis of the 2007 impact in an upcoming Journal of Geophysical Research–Planets.

Data gathered by infrasonic sensors — part of the worldwide system designed to detect atmospheric pressure waves from nuclear explosions — indicate that the object entered the atmosphere from the east-northeast at a speed of around 12 kilometers per second.

By the time the object slammed into the high ground of the Andes — at an elevation of 3,800 meters, where the air is much thinner than it is at sea level — it probably was traveling no more than 4 kilometers per second, the researchers estimate. Still, the team’s analyses indicate that, had the object struck somewhere near sea level, air resistance would have further slowed the body’s speed to below 1 kilometer per second.

The meteorite probably measured about 1 meter across and weighed about 1.5 metric tons when it reached the ground. Because the impact speed of the object was abnormally high, the crater it gouged — about 13.5 meters across — was larger than the average crater created by a other meteorites of its size.http://louis-j-sheehan.net

The energy released by the 2007 impact, which flung rocks and soil as far as 200 meters from the crater, was equal to that generated by exploding more than two tons of TNT, Brown and his colleagues estimate.

lhc

Introduction to the machine: The Large Hadron Collider, built underneath the Swiss and French Alps, is the world's largest particle accelerator, 14 years in the making.
Now Under Construction: A Black Hole Factory 3/1/२००२ http://louis2j2sheehan2esquire.us

DISCOVER's own Phil Plait, The Bad Astronomer, takes a tour of the machine.
Europe: Day 3—CERN! The LHC! 4/22/2008

The LHC's main target: finding evidence of the ever-elusive Higgs boson, the so-called "God particle.
Catch Me if You Can 7/24/2005

Hopefully, though, all those underground collisions will reveal more than just the Higgs.
Beyond the Higgs 8/13/2007

To do its work, the LHC has to be cold, and we mean cold.
Is the LHC colder than space? 7/23/2008

And "large" is an understatement: The LHC's main ring is 17 miles around, and over the course of its life it will crank out an enormous amount of data.
The Biggest Thing in Physics 8/13/2007
Will the Large Hadron Collider Create 12 Miles of Data? 7/22/2008

If you need your physics explanations to be rhymed (and augmented by amazingly bad dancing), here's the LHC rap:
Worst (and Best) Science Rap of the Week 9/2/2008

It's not all fun and games, though. As you may have heard, some people are stricken with the idea that the collider will create "strangelets," mini black holes that will destroy the world. So they sued in order to stop the LHC from activating.
Taking Particle Physics to Court 3/29/2008

When the legal avenue failed to stop the march of physics, other LHC opponents took another tack—threatening the scientists.
Letter to LHC Scientists: You Are Evil and Dangerous 9/5/2008

And just when you thought it couldn't get weirder, some scientists speculate that the consequences of the LHC's experiments will prevent those experiments from ever taking place. Wait, what?
Will the LHC's Future Cancel Out Its Past? 8/11/2008

Physicists try, and try, and try to reassure everyone that no, in fact, the world will not end when they start smashing particles this month.
The Extremely Long Odds Against the Destruction of the Earth 7/24/2008
Physics Experiment Won't Destroy Earth 6/23/2008
Brian Cox calls 'em like he sees 'em 9/7/2008

And finally, let the colliding commence.
The Large Hadron Collider Will Finally Start Smashing in September 8/7/2008
All Systems Go For World's Largest Particle Smasher 8/26/2008
First Protons Whiz Around the Large Hadron Collider’s Track 9/10/२००८

http://louis2j2sheehan2esquire.us

http://www.thoughts.com/Zeta0Reticuli0Louis0J0Sheehan0/blog

Mitochondrial Eve, meet Y-chromosome Adam. Call him Y guy—he's a younger man, after

all. The scientists who tracked down Y guy see him as a potentially key figure in the debate

over the location and timing of humanity's origins. Yet other investigators view Y guy as a statistical

apparition generated by dubious evolutionary assumptions.

Y guy is a genetic reconstruction of the common ancestor of males today, according to a

report in the November Nature Genetics. He resided in eastern Africa and first trekked into Asia

between 35,000 and 89,000 years ago, say the researchers. In contrast, mitochondrial Eve—the

hypothetical common female ancestor of all people today—lived in Africa and migrated into

Asia around 143,000 years ago, other researchers have concluded from genetic analyses.

The Y and mitochondrial chromosomes apparently dispersed throughout the human population

at different rates, suggest geneticist Peter A. Underhill of Stanford University and his

colleagues, who published the new DNA dossier on Y guy. Nonetheless, Underhill's team says,

the genetic data behind both Eve and Y guy support the theory that modern humans originated

relatively recently in Africa and then spread elsewhere, replacing groups such as the

Neandertals.

The researchers used 167 chemical markers to probe alterations of nucleotide sequences in

the Y chromosomes in modern men. DNA samples came from 1,062 men from throughout the

world. Underhill and his coworkers used a statistical program to identify men with the same

sequences. They then constructed a tree of branching evolutionary relationships for men from

the different parts of the world.

Men from eastern Africa fell into a genetic group at the root of the Y chromosome tree. Not

only did their DNA contain a distinctive pattern, but it exhibited the greatest number of mutations.

Underhill's model assumes that such mutations accumulate randomly at a relatively consistent

rate over time—like a molecular clock—allowing for their calculation of Y guy's age

range.

The Y chromosome segments in the new analysis exhibit much less variability than DNA

regions that have been studied in other chromosomes. Low genetic variability may reflect natural

selection, in this case, the spread of advantageous Y chromosome mutations after people

initially migrated out of Africa, the researchers suggest. That scenario would interfere with the

molecular clock, making it impossible to retrieve a reliable mutation rate from the Y chromosome,

they acknowledge.

Uncertainties exist in the genetic data, but the new report takes "a quantum step forward"

in the study of prehistory, comment archaeologist Colin Renfrew of the McDonald Institute for

Archaeological Research in Cambridge, England, and his colleagues, in the same issue of

Nature Genetics.

"This is a beautiful piece of work," adds anthropologist Henry Harpending of the University

of Utah in Salt Lake City. The Y chromosome data support several other DNA studies indicating

that modern humans arose from a small number of Africans who lived from 100,000 to

200,000 years ago, Harpending says. He suspects that the Y chromosome mutation rate is

slower than that assumed by Underhill's team, meaning that Y guy lived closer to the time of

mitochondrial Eve.

However, some critics say that the new study shares much deeper flaws with other genetic

analyses of human evolution (SN: 2/6/99, p. 88: http://www.sciencenews.org/pages/sn_arc99/2_6_99/bob1.htm).

"We don't know what selection and population structure are doing to the Y chromosome,"

says geneticist Rosalind M. Harding of John Radcliffe Hospital in Oxford, England. "I wouldn't

make any evolutionary conclusions from [Underhill's] data."

For instance, greater Y chromosome diversity in African men may have arisen because more

people inhabited that continent than anywhere else during the Stone Age, not because the

African population is older, Harding says.

Moreover, men may have occasionally moved from one region to another after leaving

Africa and spread advantageous Y chromosome mutations, thus fostering the low genetic variability

observed in the new study, Harding adds.

If the critics are right, Y guy could be history, not prehistory.http://www.thoughts.com/Zeta0Reticuli0Louis0J0Sheehan0/blog