A new article from space.com:

http://space.com/scienceastronomy/060601_big_crater.html


The authors have used airborne radar imaging and sensitive gravity measurements to infer that a very large impact crater lies under half a mile of ice in the Wilkes Land region of East Antarctica. These measurements suggest that the crater has a diameter of 300 miles. This would be more than twice the size of Chicxulub, the crater that led to the demise of the dinosaurs.

If this mass anomaly does indeed turn out to be of impact origin, then it would certainly be cause for major disruption in Earth’s biosphere. The most obvious extinction event without a known cause is the Permian-Triassic, the so-called “Great Dying” that eliminated about 90 percent of all marine species and 70 percent of terrestrial vertebrate species.

My problem with this speculation is that other evidence simply does not support asteroid impact for End Permian. To my knowledge, the strata at the end of the Paleozoic Era (aprox. 251 million years ago) do not show any evidence of rare metals (eg. iridium) or shocked quartz. Both of these have been found in abundance at the Cretaceous-Tertiary boundary. Also, chances are not great that a meteorite would actually hit continental crust since oceanic crust, which is recycled every 200 million years, comprises 60% of the Earth’s crust. Maybe someone with more knowledge on this subject can comment.

See also:

http://www.unmannedspaceflight.com/index.p...indpost&p=56682

Speaking of giant craters, what is the largest known crater in the solar system?

It depends on whether you count Lunar and other planetary 'basins' or not. If you do, there are some biggies on the Moon, including the South Polar Aitken Basin. On Mars, we have Hellas, but there have been nods in the direction of the 'Boreal Sea' being an ancient impact basin. Venus has too young a surface (like the Earth), and Mercury has not had big basins identified (yet - wait for the MESSENGER team to find them!).

Perhaps more interesting is a calculation of crater size to diameter, in which case some of the smaller Solar System objects seem to be the front runners. As well as the ones we already know - Mimas, Vesta etc, KBOs have a suspiciously large number of twins counted among their numbers, which probably indicates a goodly number of thwacks as well.

Bob Shaw

The largest crater of our solar system is probably in Mercury by about four times bigger than ones of Earth: East Antarctica in the Wilkes Land region, south of Australia, with about 480 km of diameter

The largest crater on Mercury is the Caloris basin. A basin was defined by Hartmann and Kuiper (1962) as a "large circular depression with distinctive concentric rings and radial lineaments." Others consider any crater larger than 200 kilometers a basin. The Caloris basin is 1,300 kilometers in diameter, and was probably caused by a projectile larger than 100 kilometers in size. The impact produced concentric mountain rings three kilometers high and sent ejecta 600 to 800 kilometers across the planet.

Rodolfo

Here she is:

http://www.solarviews.com/raw/merc/calorisl.gif

Ustrax:

You weren't hiding Caloris while I was typing, were you?

Bob Shaw

No. The biggest known impact crater in our Solar System is on our very own little Moon: the Aitken Basin, fully 2500 km wide (one-quarter of the way around the entire Moon!)

I want to point out that this Antarctic crater discovery is a major success
for NASA's GRACE satellite pair, one of the FBC Earth Science missions. This
mission has produced a lot of good science, on a low budget.

In addition, this discovery of a density variation in a Polar ice deposit,
utilizing data from a NASA satellite program reminds me very much of the
plot of one of Dan Brown's pre-DaVince Code novels, "Deception Point."
It's not a bad book and goes into a discussion of the worth of NASA to
the nation.


Another Phil

Yup. There's also the purported "Procellarum Basin" which, if it really exists, would be pretty large. However, from what I gather on various 'net sites, its existence is disputed.

There's also the idea that the disparity in crustal thickness between the near and far sides of the Moon is an age-old remnant of a huge "Vesta-like" impact that blew most of the nearside crust around the Moon to the farside. However, I've no idea whether this notion is taken seriously by selenologists.

KILLER CRATER MAY HAVE SPAWNED AUSTRALIA (Space & Astronomy News, 5/6/06)

Remains of a giant Antarctic crater could be evidence of a meteorite that
caused Earth's biggest mass extinction and triggered the break up of
Gondwana, scientists say.

http://abc.net.au/science/news/space/Space...ish_1654155.htm

The breaking up of Gondwana? Yep, Velikovsky is back.


Continent breaking is in no way related into faults in it. Note that continent breaking is a slow process, due to modifications into the convection patterns into deep mantle. Even if you could dig a trench 200kms deep 100kms wide into a continent, this would not break it if convection patterns push on both side. But if convection currents pull on both side, like in Africa now (rift valley) even a continent of steel would break.

I'll speculate that that a large enough impact could remove enough granitic crust to expose the basaltic mantle to water which could produce a phase change and "jumpstart" the continental drift engine. Pure speculation.

I'd imagine that the largest crater, ever, could be the one formed when the supposed Mars-sized body collided with the Earth when the Moon was formed.

Again, pure speculation.

--Bill

After studying the Australia and Antartica map, both continents, the south of Australia and the north of Antartica have an inside arch, so it increases the suspicsion of the big crater impact.

If the Moon was a mass of Earth, the lost mass and the add mass by the other Mars' size planet (only hypothesis) would be a part of Earth which was a "sea" before the formation of Earth's continents were all connected into one huge landmass called Pangaea. This huge supercontinent was surrounded by one gigantic ocean called Panthalassa which might probably was the impact zone between the Earth and the other "Mars' size alike".

http://volcano.und.edu/vwdocs/vwlessons/le...ea/Pangea1.html

The above Web has a peculiar theme which is how will the continent be formed within 50 millions years. North and South America are separeted. Mediterrean Sea will be much bigger and open, Spain and North Africa will be joined, and Australia will be higher than Guinea.

http://www.scotese.com/earth.htm

The above Web URL have very interesting details about the History of Earth concerning to plates, climate, etc.

The oldest and supercontinent known was Rodinia, which formed 1100 million years ago. The Late Precambrian was an "Ice House" World, much like the present-day.

Rodolfo