[blam]

Ping.

[airborne]

They proposed a theory that said a giant asteroid crashed into the Earth and spewed smoke, dust and iridium into the sky. This blocked the sun and lowered the Earth's temperature, which killed plants and animals.

When?

[JAWs]

A geologist won? That rocks!

[Verginius Rufus]

I'm not sure this theory can be considered "finally proven." For a while about a decade ago I was on Mickey Rowe's Dinosaur List, which had a lot of very knowledgeable paleontologists on it, and at that point not everyone was in agreement with Alvarez.

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?")

[trane250]

No mention of the actual scientist who came up with the asteroid collision theory- Nobel prize winning physicist Luis Alvarez, father of Walter.

Reminds me of another father-son physicist-geologist team, Albert and Hans Albert Einstein. The story goes that Hans Albert was working on a theory to predict silt buildup behind a dam funded by the Tennessee Valley Authority. Well Hans Albert got stuck and asked his father for help. It didn't take Albert long to come up with the right formula. In so doing, he showed why rivers meander instead of flowing in a straight line.

[null and void]

I highly recommend "T Rex and the Crater of Doom" by Walter Alvarez.

Is a very good and entertaining read on geology and the search for what killed of the dinosaurs.

[Mike Darancette]

The Associated Press reports the University of California-Berkeley scientist came up with the theory that dinosaurs were killed off when a comet or asteroid crashed into the Earth.

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".

[SunkenCiv]

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.

Asteroids: Deadly Impact National Geographic	Rain of Iron and Ice: The Very Real Threat of Comet and Asteroid Bombardment by John S. Lewis

[SunkenCiv]

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[SunkenCiv]

Plot of the Innermost Solar System
Minor Planet Center
http://cfa-www.harvard.edu/iau/lists/InnerPlot2.html

[SunkenCiv]

Night Comes to the Cretaceous
by James Lawrence Powell
reviewed Nov. 24, 1998
by Clark R. Chapman

[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.

Night Comes to the Cretaceous by James Lawrence Powell

[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.

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?

[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]

and BTW, thanks Blam!

Physics News Update Number 16 (Story #2)
by Phillip F. Schewe and Ben Stein
January 10, 1991

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.)