[SunkenCiv]

Evidence Of Meteor Impact
Found Off Australian Coast
by Donald Savage
May 13, 2004

Most scientists agree a meteor impact, called Chicxulub, in Mexico's Yucatan Peninsula, accompanied the extinction of the dinosaurs 65 million years ago. But until now, the time of the Great Dying 250 million years ago, when 90 percent of marine and 80 percent of land life perished, lacked evidence and a location for a similar impact event. Becker and her team found extensive evidence of a 125-mile-wide crater, called Bedout, off the northwestern coast of Australia... During recent research in Antarctica, Becker and her team found meteoric fragments in a thin claystone "breccia" layer, pointing to an end-Permian event. The breccia contains the impact debris that resettled in a layer of sediment at end-Permian time. They also found "shocked quartz" in this area and in Australia... Quartz can be fractured by extreme volcanic activity, but only in one direction. Shocked quartz is fractured in several directions and is therefore believed to be a good tracer for the impact of a meteor... The Bedout impact crater is also associated in time with extreme volcanism and the break-up of Pangea. "We think that mass extinctions may be defined by catastrophes like impact and volcanism occurring synchronously in time," Becker said. "This is what happened 65 million years ago at Chicxulub but was largely dismissed by scientists as merely a coincidence. With the discovery of Bedout, I don't think we can call such catastrophes occurring together a coincidence anymore," she added.

[SunkenCiv]

related to msg #5:

Hunt for Oil Leads to Crater Linked to 'Great Dying'
by Robert Roy Britt
13 May 2004

The team, led by geologist Luann Becker of the University of California, Santa Barbara examined undersea drilling samples taken by oil prospectors in the 1970s and '80s and since held in an Australian lab. They also studied ancient layers of Earth now exposed on land Down Under and in Antarctica. Dated to the time of the mass extinction, they found breccia, a porous rock often linked to impacts. And they uncovered tiny glass beads and material known as shocked quartz, which has been fractured in several directions. These can be indicators of the extreme heat generated when a large, high-speed extraterrestrial object slams into the planet... The findings point to the existence of a 125-mile-wide (200-kilometer) crater called Bedout off the northwest coast of Australia. The ring-like structure had previously been identified as a possible impact crater by seismic data and a map of gravity variations in the area.

[SunkenCiv]

Kerry Emanuel's hypercane idea can be found online using a Google search, here's one from the hard drive:

Were Dinosaurs Blown Away?

Unlike an asteroid, a hypercane would send into the atmosphere not dust, but large quantities of water. The model shows that the water would create sheets of new clouds, which would block out the sun, disrupt radiation patterns, and perhaps trigger ozone depletion.

When large impacts happen on water, the blast wave will be worse than any kind of storm brewed up by it, it just won't last very long. And the impact itself WOULD put water into the atmosphere -- lots of it.

[SunkenCiv]

Ancient Impact Turned Part of Earth Inside-Out
by Robert Roy Britt
4 June 2004

A space rock the size of a large mountain hit 1.8 billion years ago and dredged up part of Earth's lower crust... The evidence comes from a crater in Sudbury, Ontario. Most of the crater was long ago folded into the planet or eroded away. But a section is exposed, revealing minerals and other features that can be compared to more recent craters that are more intact. From all this, scientists gleaned clues to the catastrophic impact. It appears an asteroid about 6 miles (10 kilometers) wide hit the planet at more than 89,000 mph (40 kilometers per second)... Mungall explained that in the top layers of the Sudbury structure, his team found relatively high concentrations of iron, nickel and platinum, stuff that is more common in the lower crust of the planet than in the upper crust (the elements exist in just trace amounts in both regions)... The top layers were also relatively depleted of zirconium, uranium and other elements that tend to show up in other impact sites that only involved melting of the upper crust... Mungall's team also found an enrichment of iridium in the overlying layer at the Sudbury complex, which was already thought to be part of an impact crater.

[SunkenCiv]

Scientists Confirm Age Of The Oldest Meteorite Collision On Earth
Stanford University

The meteorite that led to the dinosaur extinction produced spherule deposits around the world that are less than 2 centimeters deep. But the spherule beds in South Africa and Australia are much bigger -- some 20 to 30 centimeters thick. A chemical analysis of the rocks also has revealed high concentrations of rare metals such as iridium -- rare in terrestrial rocks but common in meteorites...

The Earth may have been smooth as a cue ball though:

He and his colleagues point to evidence showing that, 3.5 billion years ago, Earth was mostly covered with water.

This very early impact wasn't the last:

In addition to the 3.47-billion-year-old impact, Lowe and Byerly have found evidence of meteorite collisions in three younger rock layers in the South African formation. According to Lowe, the force of those collisions may have been powerful enough to cause the cracks -- or tectonic plates -- that riddle the Earth's crust today.

The cracks (not plates) have extraterrestrial causes, and are not due to continental drift.

He also pointed to uncertainty among scientists about what the climate of the Archean Earth was really like. In a forthcoming study, Lowe will present evidence that the average temperature of the planet back then was very hot -- perhaps 185 F (85 C).