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What are meteors and meteorites?

Meteors are objects of stone or iron from outer space which enter the earth’s atmosphere as glowing balls. Those that “survive” this journey and fall onto the earth’s surface are called meteorites.

Meteorites have their origin in our own solar system, and with some few exceptions, all come from the asteroid belt between Mars and Jupiter. Dating as to age has shown that the meteorites from the asteroid belt were formed 4.5 to 4.6 billion years ago, which is reckoned to be the age of our own solar system. This is somewhat older than our own planet, which is now estimated to be 4.3 billion years. Meteorites from Mars or the moon are however much younger, from 1.5 billion years to as young as 180 million years. The asteroid belt can be regarded as the remains of an attempt to form a planet. But Jupiter put an effective end to this due to its enormous force of gravity. In this belt there are millions of stones, from some ten centimetres to several hundred kilometres in diameter. Collisions between these asteroids are the cause of most of the meteor impacts on the earth. Some meteorites have been through several collisions and changes during their journey through the solar system. Several hundred tons of stone from space fall onto the earth daily, mostly as small particles with a diameter of only a few millimetres.

Knowledge concerning meteorites is fundamental to our understanding of the origin of the solar system and of the geological processes outside of the earth. In the course of recent decades a great number of meteorites have been found in Antarctic and in deserts. The reason for this is that in such areas, lacking vegetation, they are far easier to discover than in other habitats, but also because the process of decomposition takes place more slowly. Most of these finds are of meteorites that have already remained on the earth’s surface for a long time. There have in all been found about 31,000 meteorites. The name “meteorite” has its origin in the Greek word “meteoron” which means “phenomena from heaven”.

A little history

Throughout history there have been many written descriptions of fire balls and “stones from the sky”, without knowing anything about their origin. In earlier times, just as today, meteor impacts were witnessed by many, and in some cases black stones were found. In the year 467 BC a great fire ball was described; this was observed in daylight by many people at Thrace in Greece. The meteorite was found, and Aristotle, who at the time thought that stones could only be formed on earth, suggested that it had been lifted by strong winds before falling down to the earth again! On 7th November 1492 a large stone fell over Ensisheim, Alsace in France, which at that time was part of Germany. The fall was witnessed by a youth who found the meteorite and showed it to the villagers. King Maximilian of Germany passed Ensisheim three weeks later. He studied the stone, and proclaimed that this was God’s wrath over the Frenchmen. He ordered that the stone be placed in a church as a reminder of God’s participation in the territorial conflict in the area! The meteorite is now exhibited in the town hall of Ensisheim. In the years 1600 – 1700 there were also discussions in scientific circles about the origin of meteorites. One theory was that they were formed of particles and lightning in the clouds. At that time religion was a strong force, and it was rather controversial to challenge belief in the works of God. In 1794 hundreds of stones fell over Tuscany in Italy, and over 200 stones were picked up by inhabitants and tourists. Again there were discussions concerning their origin, and one suggestion was that they came from volcanic clouds following activity of the volcano Vesuvius. The same year a German scientist named Ernst Friedrich Chladni wrote a 63 page report about “heavenly stones”. He had collected and studied historical records of the phenomenon, and concluded that these must be stones from space. Such a suggestion gave rise to no less discussion! But Chladni was of course right, and during the 1800’s, when the study of outer space became more common, this theory became ever more accepted.

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