Source: ABCnews (via Ndunlks)
Date: 15 July 1998
Written by: Lee Dye

One paleontologist has argued that extinctions seem to occur at 26-million-year intervals. That suggests to some that once every 26 million years something beyond Earth dramatically impacts our planet.
Five major extinctions, including that of dinosaurs, have occurred over the past 570 million years. Cosmic rays may have played a role.

Just when you finally thought you knew what wiped out the dinosaurs, three scientists have a new explanation that offers a whole new twist.     
Dinosaurs rank at the top of billions of species that thrived and then vanished forever. The mass extinction has perplexed scientists ever since they began digging up fossils of creatures no longer on Earth.     
David M. Raup, a statistical paleontologist at the University of Chicago, estimates that between 5 billion and 50 billion species existed at one time or another on this planet, compared to about 40 million today.     
Only about one in a thousand species is still alive a truly lousy survival record: 99.9 percent failure, Raup noted in his 1991 book, Extinction: Bad Genes or Bad Luck?     
What caused critters that survived for millions of years to suddenly disappear?     
The latest, and one of the most intriguing, forays into the debate comes from three scientists at the Israel Institute of Technology. Astrophysicists Arnon Dar, Ari Laor and Nir Shaviv speculate that radiation from the collision of distant stars caused some mass extinctions. In the last few seconds of a binary neutron star's life, the two stars spiral together and form a black hole surrounded by a hot, dense disk that blasts powerful jets. These cosmic rays may have changed life on Earth.

Mutants on Earth
At the same time, they argue in a report published in the June 29 issue of Physical Review Letters, the radiation would cause mutations, leading to the emergence of entirely new species on Earth.     
They call it their doom and creation theory.     
According to the scientists, it begins with the collision of two neutron stars remnants of supernova explosions in which the mass of several suns is packed into a ball about 12 miles in diameter. Such a violent collision blasts out jets of high-energy particles called cosmic rays.     
If Earth passed through one of these jets within about 3,000 years of the collision, the scientists theorize, the cosmic rays would be intense enough to destroy the ozone layer that protects Earth from harmful solar radiation, and make much of the planet highly radioactive.     
Radioactive particles can destroy an organism’s central nervous system and cause death within days. Scientists have documented at least five major extinctions, in which many forms of life were eliminated, over the past 570 million years, as well as many lesser events in which only a few species died out.

Out with the Old
Past mass extinctions, and there have been many, have frequently been followed by the sudden rise of new species as though whatever killed off the old brought in the new.     
Cosmic rays could do that, the scientists argue, and much evidence should be awaiting discovery in the rocks and fossils of ancient Earth. A high-energy particle smashing through a rock leaves a track. Sensitive instruments should be able to find those tracks.     
The scientists are calling on their colleagues around the world to search for evidence of high energy particles in fossils and rocks that correspond in age to known periods of mass extinctions.     
No one will know if the scientists are on the right path unless that evidence can be found.     
It may all sound a bit bizarre, but no more so than the most popular theory about mass extinctions. The scientific community generally accepts that an asteroid or comet smashed into Earth 65 million years ago, wiping out the dinosaurs.     
That wasn’t always the case.     
As luck would have it, I was present when the father-and-son team of Luis and Walter Alvarez went public with their theory at a science meeting in 1980.

A Sun-Starved Planet
Luis, a Nobel prize-winning physicist and the father of Walter, a geologist, postulated that an asteroid smashing into Earth would kick enough debris in the atmosphere to cool the planet. That would have killed most of the plants on which the dinos dined.     
The Alvarez team had some evidence to back up their claim. While excavating fossils near the town of Gubbio, Italy, they found a layer of red clay that formed just as the dinosaurs were dying out.     
The clay turned out to be rich in iridium, a heavy metal usually found only deep within Earth, and in meteorites. That led to the speculation that the iridium came from the impact of a large asteroid or comet, which could have precipitated changes in global weather that killed the dinosaurs.     
Had it not been for the scientific credibility of the two men, and that dab of evidence, they would have been hooted out of the hall. Instead, scientists around the world began looking for more evidence. Surprisingly, they found a layer of iridium that literally circled Earth, deposited at precisely the time that the dinos were going down.     
A few paleontologists still argue that the dinosaurs died out over a period of several million years, and thus were not likely to have been the victims of a cataclysmic collision.

Still a Mystery
The two theories asteroid or cosmic rays don’t necessarily conflict. There could be many reasons for different extinctions. Raup, for example, has argued that extinctions seem to occur at 26-million-year intervals. That suggests to some that once every 26 million years something beyond Earth dramatically impacts our planet.     
That, in part, gave rise to the search for a Death Star, a companion to our sun that sweeps through the neighborhood once every 26 million years, causing all sorts of havoc. Nobody has found a trace of it yet.     
But we do know that neutron stars collide, sending out cosmic rays. Five pairs of neutron stars are expected to collide within our galaxy. But in each case, the collision is several hundred million years away.     
There are probably many more, as yet undiscovered. So are we in immediate danger?     
The scientists speculate that any such pending collision would be detected hundreds of thousands of years in advance. That leaves us plenty of time to build cosmic ray shelters.

Science writer Lee Dye’s column appears Wednesdays on ABCNEWS.com. Copyright (c)1998 ABCNEWS and Starwave Corporation. All rights reserved.

Back to Main Articles Page
Former Article on this subject

This page hosted by Get your own Free Home Page