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,)

Metric units & English measurement (The importance of units)

In December 1998 NASA launched the 125-million dollar Mars climate orbiter,intended
as the red planet's first whether satellite. After a 416-million mi journey,the
spacecraft was supposed to go to Mars' orbit on September 23,1999. Instead entered
Mars' atmosphere about 100 km (62 mi) lower than planned and it was destroyed by heat.
The mission controllers said the loss of spacecraft was due to the failure to convert English
measurement units into metric units in the navigation software.


    Engineers at Lockheed Martin Corporation who built the space craft specified
its thrust in pounds,which is an English unit. Scientists at NASA's Jet Propulsion Laboratory,
on the other hand,had assumed that thrust data they received were expressed in metric units,as newtons.
Normally,pound is the unit of mass.Expressed as a unit of force,however, 1 lb is
the force due to the gravitational attraction on an object of that mass.
To carry out the conversion between pound and newton,we start with,
 1 lb = 0.4536 kg and from Newton's second law of motion,

                     force = mass * acceleration
                           = 0.4536 kg 9.81 m/s^-2
                           = 4.45 kg m/s^-2
                           = 4.45 N

because 1 newton(N)=1 kg m/s^-2.therefore,instead of converting one pound of force to
4.45N,the scientists treated it as 1N.

        The considerably smaller engine thrust expressed in newtons resulted in a
lower orbit and the ultimate destruction of the spacecraft.Commenting on the failure
of the Mars mission,one scientist said : "This is going to be the cautionary tale that will be embedded into introduction to the metric system in elementary school high
school,and college science course till the end of time."

 

Primordial Helium and Big Bang Theory

Where did we come from? How did the universe begin? Humans have asked these questions for as long as we have been able to think. The search for answers provides an example of the scientific method.

In the 1940s the Russian-American physicist George Gamow hypothesized that our universe burst into being billions of years ago in a gigantic explosion, or Big Bang.In its earliest moments,the universe occupied a tiny volume and was unimaginably hot.This blistering fireball of radiation mixed with microscopic particles of matter gradually  cooled enough for atoms clumped together to make billions of galaxies including our Milky Way Galaxy.

Gamow's idea is interesting and highly provocative.It has been tested experimentally in a number of ways.First, measurements showed that the universe is expanding;that is,galaxies are all moving away from one another at high
speeds.this fact is consistent with the universe's explosive birth. By imagining the expansion running backward,
like a movie in reverse,astronomers have deduced that the universe was born about 13 billion years ago.The second observation that supports Gamow's hypothesis is the detection of ;;cosmic background radiation;; Over billions of years,the searingly hot universe has cooled down to mere 3K(or-270 C)! At this temperature,most energy is in the
microwave region.Because the Big Bang would have occurred simultaneously throughout the tiny volume of the forming universe,the radiation it generated should have filled the entire universe.Thus,the radiation should be the same on any direction that we observe.Indeed,the microwave signals recorded by astronomers are independent of direction.

The third piece of supporting Gamow's hypothesis is the discovery of primordial helium. scientist believe that helium and hydrogen(the lighted elements)were the first  element formed in the early stages of cosmic evolution.(The heavier elements,like carbon,nitrogen and oxygen,are thought to have originated later via nuclear reactions involving hydrogen and helium in the center of stars) If so,a diffuse gas of hydrogen and helium would have spread through the early
universe before much of the galaxies formed. In 1995 astronomers analyzed ultraviolet light from the distant
::quasar::(a strong source  of light and radio signals that is thought to be an exploding galaxy at the edge of the
universe)and found that some of the light was absorbed by helium atoms on the way to earth.Because this particular quasar is more than 10 billion light-years away(a light year is the distance traveled by light in a year),the  light reaching Earth reveals events that look place 10  billion years ago.Why wasn't the more abundant hydrogen detected?
A hydrogen atom has only a one electron,which is stripped by the light from a quasar in a process known as
ionization. Ionized hydrogen atoms cannot absorb any of the quasar's light. A helium atom,on the other hand,has
two electrons. Radiation may strip a helium atom of one electron,but not always both. Singly ionised helium atoms
can still absorb light and are therefore detectable.

Proponents of Gamow's explanation rejoiced at the detection of helium in the far reaches of the universe.
In recognition of all the supporting evidence,scientists now refer to Gamow's hypothesis as the BIG BANG THEORY.