I just took a look at this month's archives. Someone posted this announcement on the Dinosaur List on March 6, and one of the list members, Gautam Majumdar, pointed out that M. W. De Laubenfels had proposed an impact as the cause of the KT boundary mass extinction back in 1956 already.
Another list member linked to a press release from the University of Leicester about the work of two geologists at that university who argue for volcanism rather than an extraterrestrial impact as the cause of the mass extinctions. (The press release is entitled "Mass Extinctions -- A Threat from Outer Space or Our Own Planet's Detox?")
Well deserved. I hope he uses some of that money to drink a toast to his dad the late Luis Alvarez who was instrumental to that find.
In Walter's book "T-Rex and the Crater of Doom" he has one of my favorite opening lines; "65 million years ago the Earth had a bad day".
M. W. De Laubenfels had proposed an impact as the cause of the KT boundary mass extinction back in 1956 already.That's interesting, I'm not sure I'd read that before. The Alvarez theory came to public attention circa 1980; an earlier attempt to use large impact as an explanation for the Great Dying was published in 1970 by someone else, and fell into the void. Pemex identified the crater in 1960 (!) without consideration of the origin or any connection with extinctions, and one of the Pemex geologists pointed it out to Luis circa 1980 -- without getting any response. The Chicxulub crater was finally fingered in 1990. The important role of impact wasn't finally victorious (and it has been victorious, despite the claims of some carpers among volcanologists) until 1994, when SL-9's fragments crashed one by one into Jupiter.
Rain of Iron and Ice:
The Very Real Threat of
Comet and Asteroid Bombardment
by John S. Lewis
Plot of the Innermost Solar System
Minor Planet Center
Night Comes to the Cretaceous[W]ith no generally accepted explanation for the dinosaurs' sudden demise, there was no broad, unified defense of an alternative to the Alvarez proposal. Nevertheless, as Powell documents, it was no easy road to acceptance of the idea, especially among paleontologists. One prominent astronomer even argued against the impact hypothesis... Powell finally realizes that the burden of proof has shifted to the anti-impactors... This is a well-written, intelligent book, accessible to the interested layperson but also fully footnoted for geoscientists who want more technical details. It is a thorough account of that portion of the K-T battle, now won, that was fought on a geological turf.
by James Lawrence Powell
reviewed Nov. 24, 1998
by Clark R. Chapman
Night Comes to the Cretaceous
by James Lawrence Powell
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.
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).Was the much higher temperature due to the energy of the impact (duh!)? Or is this just another excuse to shill about the effect of so-called greenhouse gases?
Ancient Impact Turned Part of Earth Inside-OutA 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.
by Robert Roy Britt
4 June 2004
Physics News Update Number 16 (Story #2)The far side of the Moon, impossible to see from the Earth, was recently photographed by the Galileo spacecraft on its way toward Jupiter. New information about the mineralogical composition of the far side's crust was recorded and pictures revealed the largest impact basin yet seen on the moon, more than 2000 km in diameter and so deep that is may have penetrated through the crust to the moon's mantle. (Eos, January 1, 1991.)
by Phillip F. Schewe and Ben Stein
January 10, 1991