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Re: (Another)New Theory on Dinosaur Extinction

           I'm always open to alternate theories on the dinosaur's disappearance
           65 million years ago.  Ginsburg ideas seem to provide
           additional evidence for the comet/asteroid impact theory, a theory
           he claims is wrong.  Ginsburg also does not adequately explain
           the presence of iridium in the 65 million year old layers, something
           he claims is created by evaporating water.

>           The trouble is, few people outside France want to listen.
>           Ginsburg, professor of palaeontology at the French Natural
>           History Museum, published his first thesis on the extinction of
>           the dinosaurs more than 30 years ago.
>
>           He believes his basic argument, that a gradual drop in world sea
>           levels led to disastrous climate changes for the huge reptiles,
>           still holds good but that more eye-catching theories have
>           captured the public imagination.

           Actually, the Alvarez comet/asteroid impact theory was met with a
           lot of skepticism when first proposed in 1980.  It was only after
           additional evidence surface, such as the discovery of iridium in the
           65 million year old sedimentary layer around the world, and the 
           discovery of a large 65 million year old crater in the Yucatan, 
           that the theory accepted by the main stream scientists.  

>           His main bug-bear is a U.S. hypothesis that the dinosaurs were
>           wiped out after a giant meteorite smashed into the Earth with a
>           force estimated at five billion times that of the Hiroshima
>           nuclear bomb.
>
>           ``This is ridiculous,'' Ginsburg says. ``It is obvious the dinosaurs
>           died over the space of millions of years and not in one
>           cataclysmic event. The trouble is Americans like wonderful
>           disaster scenarios and my idea is not spectacular enough.''

           The fossil record clearly shows that ALL dinosaurs perished
           rather suddenly 65 million years ago. 

>           Ironically, says Ginsburg, solid evidence that the dinosaurs
>           slowly dwindled into oblivion rather than blasted off the face of
>           the Earth by a meteorite has been found in the United States
>           itself, in fossil sites in the state of Montana.
>
>           Digs have shown that 75 million years ago there were 30 species
>           of giant reptile living in the area. Five million years later there
>           were 23, within two million years the number had fallen to 18,
>           and so on down until the end of the so-called Cretaceous period
>           when all the dinosaurs had died out.

           I don't doubt that some species of dinosaurs were slowly dying out
           prior to the 65 million cutoff point.
           Ginsburg seem to focuses on a localized area, and on a pattern that
           does not fit the pattern world wide.  Ginsburg would have a stronger
           case if he can show that ALL dinosaurs were gradually dwindling.
           He would also have to show why ALL dinosaurs became extinct at
           the SAME TIME 65 million years ago.

>           Ginsburg believes that a common element probably tied all of
>           these events together -- sea movement caused either by changes
>           to the polar icecaps or shifts of the Earth's crust.

           Ginsburg does not explain the causes of these changes.
           An interesting point is that a large impact on Earth could
           cause these effects, so Ginsburg could be inadvertantly providing
           data for the comet/asteroid impact theory.

>           ``Each major division in the geological time-scale begins with
>           the spread of sea over land areas, accompanied by the
>           appearance of new fauna, and ends with the sea shrinking again
>           which causes a massive loss of life,'' Ginsburg says.

           A nuclear winter following an asteroid/comet impact would result
           in a growing ice pack at the Earth's poles, resulting in the
           lowering of the oceans. After the nuclear winter ends, the
           ice pack would melt and the oceans would resume their normal
           levels.  

>           What was remarkable about the sea's retreat during the fateful
>           Cretaceous period was the scale of the move.
>
>           Water used to cover most of Europe, all of North Africa, the
>           Sahara, the Middle East and a large chunk of northwestern South
>           America.
>
>           Then the seas inched back from their original coastline, most
>           notably in Europe where the waters receded thousands of
>           kilometres (miles), to end up close to their present shores.
>
>           The dramatic change annihilated 80 percent of life on Earth,
>           killing off not just the dinosaurs but a whole range of species on
>           land and in the sea, Ginsburg says.

            Dramatic change?  I thought Ginsburg was claiming a gradual
            change in the sea level was the cause of the demise of the
            dinosaurs.  So which is it?  A gradual change, or a dramatic
            change?

            Again, nothing to rule out the comet/asteroid impact theory, 
            particularly if a dramatic change is claimed.

>           One of the most famous marine victims were ammonites, the
>           beautiful spiral molluscs so beloved of fossil hunters which had
>           survived for 300 million years before succumbing to extinction
>           as their shallow water habitat got sucked away.

           As long as there is an ocean, shallow water habitats will always 
           exist, no matter where the sea level is.  If there is a gradual
           drop in the sea level, then the ammonites would surely have time
           to move to the new locations of the shallow waters.  Their
           disappearance is more indicative of something occuring quickly
           and on a global scale.  If it was a dramatic change, then
           that leads right into the comet/asteroid theory.

>           But why were land-based dinosaurs affected by the sea? GIANT
>           DINOSAURS SENSITIVE AT HEART As more land became
>           exposed, so the world's climate was transformed.
>
>           ``The previous tropical climate became increasingly continental,
>           bringing wider differences between winter and summer and
>           between night and day. The dinosaurs simply could not cope,''
>           said the white-haired professor.
>
>           To demonstrate their sensitivity to temperature, Ginsburg points
>           to the alligator -- which only just managed to claw its way out of
>           the Cretaceous period.
>
>           Tests have shown that between 32 and 34 degrees centigrade (89
>           and 93 degrees Fahrenheit), incubating American alligator eggs
>           will only hatch as males while between 28 and 30 centigrade
>           (82 and 86 degrees fahrenheit) they produce females.
>
>           ``If such a small temperature drop is enough to ensure that no
>           male alligators are born, the drop of about eight degrees
>           centigrade seen in the late Cretaceous period was surely enough
>           to eliminate entire reptile groups -- specifically dinosaurs,''
>           Ginsburg maintains.

           And all of this fits in very well with the comet/asteroid impact
           theory.

>           Warm-blooded animals, like mammals, managed to survive the
>           cooler climes. Reptiles, which are cold blooded and highly
>           susceptible to the surrounding temperature, struggled to adapt
>           and most perished.
>
>           ``Dinosaurs were like oil tankers. They needed a long time to
>           change course and ultimately never made it,'' Ginsburg said.

           Ditto.

>           The explanation most often cited involves the killer comet -- a
>           view first aired by U.S. geologist Walter Alvarez in 1980.
>
>           He argued that large amounts of the metallic element iridium
>           found in sediments deposited at the end of the Cretaceous period
>           indicated that a huge meteorite had struck home.
>
>           A rare element, iridium is found in abundance on meteorites.
>           Alvarez believes a chunk of the extra-terrestrial matter hit Earth
>           with such force it raised a suffocating dust cloud which spread
>           iridium around the globe and shut out the sun for years.
>
>           But Ginsburg argues that the iridium could equally well have
>           been left by the pockets of evaporating water.  

           Some elaboration is definitely needed on this point.  I would
           like to see explaination on how iridium, a rare element on Earth,
           suddenly materializes out of thin air when water evaporates. 
           Also, water is evaporating in massive quantities around the Earth
           all the time, and if they somehow left iridium deposits, we
           would see them all over the place.

Ron Baalke