Note: this topic is from 2/18/2002.
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Posted on 02/18/2002 12:59:05 PM PST by RightWhale
http://www.observer.co.uk/uk_news/story/0,6903,651829,00.html
How star blasts forged mankind
Cosmic radiation two million years ago had a crucial impact on our evolution
Robin McKie
Sunday February 17, 2002
The Observer
They are the most destructive events in the universe, vast eruptions that rip apart stars and blast radiation across space.
But supernovae may also play constructive roles in the cosmos - recent scientific research has revealed that these stellar annihilations had a crucial impact on human evolution.
Two million years ago, just as the Earth's primitive apemen were evolving into big-brained humans, a pair of supernovae explosions occurred near Earth.
Our planet was buffeted with blasts of radiation - with devastating effects. 'These supernovae would have blown away our protective ozone layer,' said Dr Narciso Benítez, of Johns Hopkins University, Baltimore.
'Earth lost its protection against ultraviolet solar rays and for several hundred years the planet would have been battered by intense radiation. All sorts of mutational damage to animals' DNA would have occurred. New species could have emerged as a result. It is possible Homo sapiens may have been one of these.'
A supernova occurs when a hot, dense star burns up its fuel too quickly and suddenly implodes, generating shock waves and intense blasts of radiation across space. When a supernova explodes, it outshines all the other 200 billion stars that make up our galaxy, the Milky Way.
The likely impact of a supernova's radiation led scientists in the past to speculate that one may have affected evolution on Earth. But calculations indicated that fields of interstellar gas would have dissipated a supernova's radiation and blunted its impact.
However, Benítez and his colleague, Dr Jesús Maíz-Apellániz, of the Space Telescope Science Institute in Baltimore, now believe that at least two supernovae occurred near Earth two million years ago. The first would have blasted space free of interstellar particles; the second would have struck Earth at full force, destroying its ozone layer.
'Supernovae are very rare. So two such explosions occurring relatively close together might seem unlikely. However, we have discovered that around this time a group of hot, dense young stars - just the type that turn supernova - passed relatively close to Earth,' said Maíz-Apellániz.
'Some of this group - known as the Sco-Cen group - would have got within 100 light years of us, which, astronomically, is not a great distance. Our calculations suggest that two or three of these exploded as supernovae.'
In short, Earth was hit by an astronomical double whammy - though the discovery that supernova-prone stars passed near Earth two million years ago does not, on its own, provide complete proof, as the two scientists admit.
However, further support for the theory, to be published in Physical Review Letters next week, has been found by scientists studying samples of sediments from the Pacific ocean floor. German researchers recently uncovered an isotope of iron known as iron-60 in ocean bed samples laid down about two million years ago. 'Iron-60 is made by only one thing in nature - a supernova,' said Benitez. 'A supernova sprays space with many different elements.
Many are rare - like iron-60. These particles hit our atmosphere and settle like a thin layer of dust over the planet.' Intriguingly, the iron-60 layer found by the German group did not come from a single supernova but appeared to come from a number of them. 'Different layers seem to have fallen at different times, but all around two million years ago,' said Benítez.
In addition, observations of space around our Sun have revealed that unlike the rest of the galaxy, space near us has little interstellar gas in it. 'Essentially it is missing much of its dust and gas - just as if a supernova had cleaned it out,' added Maíz-Apellániz.
In other words, our tiny corner of the galaxy appears to have been swept clean by a supernova brush about two million years ago. Intriguingly, at just this time, a set of extinctions - known as the Pliocene/Pleistocene extinctions - is also known to have occurred.
Geologists have found that plankton and molluscs were wiped out in vast numbers and that land animals and plants were also affected. 'We now think these creatures were killed off because Earth's ozone was blasted away by two or more supernovae,' said Benítez.
'There would have been no protection against the Sun's intense ultraviolet radiation. All sorts of changes could have resulted.'
It was also around this time that mankind's direct ancestor, Homo erectus, the species considered to be the first true human being, appeared in Africa and Asia after replacing more primitive ape-like creatures such as Australopithecus africanus. These beings may have been some of the lucky few who were able to advantage of conditions in these hazardous, radioactive times. This triumph only occurred thanks to this celestial intervention, however.
'It is a very interesting idea,' said Professor Chris Stringer, of the Natural History Museum in London. 'Certainly, quite a number of extinctions around this period. At the same time, Homo erectus was beginning to make its way in the world.
'However, we would have to tie down the datings of the supernovae eruptions and also the dates that the layers of the iron-60 were deposited before we could start to take such an idea seriously as a cause of the changes we see in the fossil records'.
And that was a mighty long time ago. Did they have the gender-neutral translation then?
How about if we send a grad student? Cheaper, probably not as reliable as a NASA Mars lander, but available now.
How about the 5 loaves and the 5000 with remainder 7, or 7 loaves and the 4000 with remainder 12? [I may have these mixed up.]
They lived at the forest edge, staying in the shade most of the time. They would go out into the tall grass only if they saw dinner hopping by.
Supernovas create heavy atoms such as iron. Since it was freshly created material, any radioactive isotopes would still be hot compared to now, 2 million years later.
I guess. It's probably a little hyperbole. Iron-60, if it were highly radioactive, would have decayed to something else by now. Actually iron is about as stable an element as there is. The end result of the universe reaction when it goes to completion will be iron. Everything will be iron.
Yes, the author would benefit from a couple weeks at FR, refining those logical skills.
you can explain this too me---perpetual spontaneous life--matter---evolution?
Nope; no, I don't. Most people ignore what is PLAINLY written, let alone anything supposedly hidden.
I agree with you that it is utterly laughable that somebody writes some new PC thing and then still claims it is a 'bible.' Why don't they just translate Portnoy's Complaint into Arabic, or something worth while like that?
I think we were using the shell model of the nucleus as the basis for our calculations. I'm not sure though. Time for ice cream.
Note: this topic is from 2/18/2002.
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