The Mystery (The Disappearance of the Dinosaurs)

The Disappearance of the Dinosaurs


Dinosaurs dominated life on Earth for millions of years and then disappeared suddenly
To solve the mystery,paleontologists studied fossils and skeletons found in rocks in
various layers of Earth's crust.Their finding enabled them to map out which species
existed on Earth during specific geologic periods.




They also revealed no dinosaur skeletons in rocks formed immediately after the
Cretaceous period,Which dates back some 65 million years.It is therefore assumed
that the dinosaurs became extinct about 65 millions ago.

       Among the many hypotheses put forward to account their disappearance were
disruption of the food chain and dramatic change in climate caused by violent volcanic
eruptions.However there was no convincing evidence for any one hypothesis until 1977.It
was then that a group of paleontologists working in Italy obtained some very puzzling data
at a site near Gubbio.The chemical layer of a clay deposited above sediments formed
during the Cretaceous period(and therefore a layer record events occurring after the
Cretaceous period) showed surprisingly high content of the element iridium(Ir).
Iridium is very rare in Earth's crust but is comparatively abundant in asteroids.

        This investigation led to the hypothesis that the extinction of dinosaurs occurred as follows.
To account for the quantity of iridium found,scientists suggest that a large asteroid several miles
in diameter hit the Earth about the time dinosaurs disappeared.The impact of the asteroid on Earth's
surface must have been so tremendous that it literally vaporized a large quantity of surrounding rocks,
soils and other objects.The resulting dust and debris floated through the air and blocked
the sunlight for months or perhaps years.Without ample sunlight most plants could not grow.
and the fossil record confirms that many type of o\plants did indeed die out at this time.
Consequently,of course,many plant-eating animals perished,and then,in turn,meat-eating animals began to starve.
Dwindling food source obviously affects large animals needing great amounts of food quickly and more severely than animals.
Therefore,the huge dinosaurs,the largest of which might have weighted as much as 20 tons,vanished due to lack of food.

Chemical Clues

(1)    How does the study of dinosaurs extinction illustrate the scientific method?
(2)    Suggest two ways that would enable you to test the asteroid collision hypothesis.
(3)    In your opinion,is it justifiable to refer to the asteroid explanation as the theory of dinosaur extinction?
(4)    Available evidence suggests that about 20 percent of the asteroid's mass turned to dust and spread 

        uniformly
        over Earth after setting out of the atmosphere.This dust amounted to about 0.02g/cm^2 of Earth's

        surface.  
        The asteroid very likely had a density of about 2g/cm^2.Calculate the mass(in kilograms and tons)of the 

        asteroid and  its radius in meters,assuming that it was a sphere(The area of Earth is 5.1*10^(14) m^2;1 
        lb=453.6g,)