A Little History of the Earth

In the 17th century, the earth was thought to have its birthday on Oct. 22, 4004 BC at exactly 6 p.m., according to Archbishop James Usher of Armagh following his studies of the Bible. Although obviously a dedicated cleric his conclusion disregarded any understanding of geology or astronomy he may have had. The world we inhabit is 4.6 billion years old and is the outcome of a very long astronomical evolution that involved the coalescing of a massive dust and gas cloud many of thousands of years ago.

According to astronomers, the earth is said to have formed at the same time as the rest of the solar system. At first a cloud of helium and hydrogen, which was left over from the universe's Big Bang 13.7 billion years ago, was dosed with heavier elements created as other stars began to drift across space. This cloud began to slowly spin as it was compressed, it is thought, by a nearby supernova explosion. This resulted in the formation of a flat disk which became the sun and a family of orbiting planets. The third-closest planet to sun became the earth we now know.

This completely molten newborn planet was heated by the pressure of its contraction and it was under attack from interplanetary debris. The elements that were heavy, like iron, sank to form its core and so a magnetic field was generated which still protects the planet's atmosphere - key to the evolution of life. The earth cooled slowly and a solid crust was formed after about 100 to 150 million years. Volcanic eruptions vented gases into the atmosphere and water came with comet bombardments. These times, spanning 500 million years, are now known as the Hadean era. Conditions were indeed hell-like and the planet was fiery and hot. However, it is argued by some scientists that oceans were formed at this time and that the world was cooler than first believed.

Cooler or not, the earth was a very different place back then. Ammonia, nitrogen, carbon dioxide and methane were all evident in the atmosphere according to the calculations of scientists. None of the oxygen would have been free and there would have been no ozone layer. This meant a constant pouding by the sun's ultraviolet radiation. An utterly inhospitable environment. Until about 3.5 billion years ago when the very first simple living organisms appeared as chemicals coalesced.

It was at this time that the continents began to assemble. This was followed by the first in a series of supercontinents, which continue to form and be broken up by the movements of the tectonic plates. The earth's crust rests on these ever shifting plates. If two plates move apart a volcanic eruption may occur. If two plates collide earthquakes are triggered. They also account for tsunamis. So the earth is not 'formed', it is still 'forming'. Forever changing.

However although such geological activity has moulded the world as we know it, and has been and still is violent at times, it has also proved stable enough to enable the continued evolution of life forms, both complex and simple - among which is the relatively new, yet eager, group called Homo sapiens.