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Earth science

Planet Earth: two easts, two wests!

The earth’s magnetic field is due to the circular movement of the earth’s molten outer iron containing core around a solid inner core, creating a dynamo-like effect. The effects of the magnetic field extend to tens of thousands of kilometers into space above the earth. This ‘magnetosphere’ protects the earth from the damaging effects of cosmic rays, and life would not have existed in its present form without this protective effect.

After a certain period of time, ranging from tens of thousands of years to a million years, the earth’s magnetic field undergoes a reversal so that the positions of the north and south become interchanged. The process, known as a ‘geomagnetic reversal’, last occurred about 780,000 years ago, but has occurred more frequently also (twice in 50,000 years). The timing of the reversal of the earth’s magnetic field was first determined by a Japanese scientist, Motonori Matuyama, in the 1920s when he found rocks in Japan whose magnetic fields were reversed. Since then age related magnetic stripes have been found on ocean floors, indicating that reversals in the earth’s magnetic field have occurred numerous times since its formation. The earth’s magnetic field is presently getting weaker with a 10-15% decline in the last 150 years, indicating that the reversal of the poles could occur before long.

Obviously, each time the reversal of the north and south occurs, east becomes west, and the west becomes east. The planet earth has therefore had two easts and two wests many times over its life period. It is an interesting fact that in the Holy Quran, there is mention of “Rabbul Mashreqaine wa Rabbul Maghrebain” — the Lord of the two easts and the two wests! The phenomenon of reversal of the earth’s magnetic field was not known when the Holy Quran was revealed.

 Determining age of fossils/materials

Fossils have been discovered which are hundreds of million years old. How does one determine their age? The technique involves measuring the abundance of some elements. One method commonly used is called “carbon dating”. There are three forms (isotopes) of carbon: the stable forms are carbon -12 and carbon -13, while an unstable radioactive form which decays with time is carbon-14. These forms of carbon are incorporated into the plant kingdom by the process of photosynthesis (conversion of atmospheric carbon dioxide into more complex plant parts), and then, through the food chain, carbon is passed on to animals. The radioactive carbon -14 is being constantly formed in the atmosphere as a result of the bombardment of nitrogen by cosmic rays. Live plants and animals have the carbon-14 being constantly introduced from the atmospheric carbon dioxide, but once the living materials die, the amount of carbon-14 starts to diminish with time — the clock starts ticking. Carbon-14 has a “half life” of 5730 years i.e. Its amount is reduced to half after this time. After ten half lives (about 60,000 years), the amount of carbon-14 diminishes to almost zero and it is therefore not possible to find the age of plant or animal fossils older than 60,000 years by radiocarbon dating.

For determination of age of fossils older than 60,000 years one uses a potassium-argon dating technique. Potassium-40 has a half life of 1.3 billion years, thus allowing the age of rocks several billion years old to be determined.  A more accurate ‘argon-argon’ dating technique (determining the ratio between argon-39 and argon-40) has also been developed.


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