Earth and Life

 The universe is unimaginably vast. It is billions upon billions of kilometers wide and we use a special unit called light year to measure it, that is, the distance that light, which moves at a speed of about 300,000 kilometers per second, travels in one year. This distance equals to 9,400,528,405,000 kilometers. It is mind-boggling figure but still it is merely a unit of those distances that one encounters when dealing with the measure of universe. The nearest star to Earth (after the Sun), named Proxima Centauri, is 4.2 light years away and the most distant objects detected in the universe are more than 13 billion light years away from Earth. The universe is composed of many galaxy super-clusters, themselves made up of clusters of galaxies. One of these contains Milky Way Galaxy, that is, our galaxy. Our galaxy, a spiral shaped formation, contains about 200 billion stars. One such star is our Sun, the parent to a family of nine planets, including our Earth.

  Earth was formed about 4.5 billion years ago. The outer shell of Earth is divided up into large tectonic plates. These plates, which include both the continents and the floors of oceans, slowly move – called Continental Drift – at the rate of about one centimeter a year. Over geological time, entire continents have wandered around the globe, colliding into one another or drifting apart. About 360 to 286 million years ago Earth’s two great continents, named Laurasia – made up of parts of present-day Asia, North America and Europe, and Gondwanaland – made up of South America, Africa, Antarctica and Australia collided with one another, forming a single super-continent, named Pangaea. About 208 to 144 million years ago Pangaea again began to split into two and Laurasia and Gondwanaland started to drift apart again, although some pieces of land-mass such as India and Asia have collided with each other. About 144 to 65 million years ago Laurasia and Gondwanaland themselves started to break up into smaller land-masses and became the continents as we know them today.

  The period of 4.5 billion years, since the formation of Earth to the present time, a huge time- span, is divided into different periods. The time from 4.5 to 3500 million years ago is the period when formation of Earth took place. From 3500 to 530 million years ago the period is called Precambrian when primitive life originated. From 530 to 450 million years ago, the period called Cambrian, was the time when first shellfish came into being. It is called ‘Cambrian explosion’ for the reason that during this period almost all the previous primitive simple forms of living beings became extinct and a great many diversified forms of life took their place. It is speculated that during this period there was sudden increase in the level of oxygen in the sea waters (bring it to the present level) and the new life forms came into being, diversified and evolved organs like eyes and limbs, turning these life forms into predators and prey. Since Cambrian explosion, the diversified life has evolved through Darwinian evolutionary principles of natural selection and has not much changed.

From 450 to 438 million years ago, in Ordovician period, first jawless fish originated. From 438 to 408 million years ago – Silurian period- first fishes with jaw originated. From 408 to 360 million years ago – in Devonian period – first insects originated. From 360 to 286 million years ago – in Carboniferous period – first reptiles originated. From 286 to 250 million years ago – in Permian period- first Anchisaurus originated. From 250 to 208 million years ago – in Triassic period- first mammals and dinosaurs came. From 208 to 144 million years ago – in Jurassic period- first birds came. From 144 to 65 million years ago – in Cretaceous period- first flowering plants came into existence and at the end of this dinosaurs became extinct around 65 to 1.8 million years ago. At the end of this Cretaceous period first modern humans came on the scene and 1.8 million years ago to the present times – the period called Quaternary – humans evolved to the present position.

  With the new findings taking place, these periods are somewhat re-adjusted according to the findings. For example, on the basis of an Australian paleontologist Dr. Jim Gehling’s fieldwork a new period called Ediiacaran has been added. He found a pre-Cambrian layer of 600 to 543 million years ago having fossils of creatures with skeletons or shells.

  Science knows four basic properties of life: Organisms grow and develop; life-processes happen inside the organism changing their chemical substances from one form to another; they consume food, a form of energy, to power the life-processes; they re-produce themselves. There are five kingdoms of living world, namely, Monera, Protista, Fungi, Plantai and Animalia.  Monerans are the smallest and simplest organisms, which includes bacteria or germs. Each is a single microscopic cell, which does not have a nucleus, the control centre. Kingdom Protista contains single- celled organisms as well as multi-cellular algae, which have larger and more complex cells that include nucleus; Kingdom Fungi are multi-cellular and get their energy by dissolving or digesting dead and dying organisms into simple nutrients, which they absorb through their body. Plants (of Plantae Kingdom) also are multi-cellular and obtain their energy by photosynthesis from sunlight and contain 400,000 known species. And, lastly, animals (falling within Kingdom Animalia) containing over 2 million known species is the largest grouping in the classification and they live by consuming other living things. Many animals remain poorly known and it is believed that there may be about 10 million species still to be discovered. The Quaternary Period runs from about 1.8 million years ago to the present time. The Pleistocene Epoch, which occupies all but the last 10,000 years, was the time of the Ice Ages, during which, on at least four occasions, great ice sheets spread southwards and buried much of northern Europe, North America and Asia. In between, there were periods of warmer, even subtropical, climate, called interglacial. Human-like animals, called hominids, first appeared about four million years ago, but the evolution of modern human beings took place during the Ice Ages. The fossil evidence points to the grasslands of Africa being our place of origin, from where humans spread out to different parts of the world. One branch of the Homo sapiens family, called Neanderthals, adapted to the cold European climate, but died out 30,000 years ago.

  Humans – Homo sapiens – have been living on Earth for about two millions of years. Their anthropological history spanning at least ten million years has been re-constructed by scientists on the basis of their primitive ancestors’ unearthed fossils and tools. On this anthropological scale of ten million, the debut of most ancient intelligent human being on Earth is of very recent period – merely the last 20 or 30 thousand of the past 10 millions. Because of the process of continental-shift, primitive men living on a single landmass – Gondwana – got scattered, or rather distributed, on our present five continents. This process of gradual shift of continents resulting into separation from Gondwana with accompanying drastic change of climates itself has taken a period of at least five million years. It is a very long period and nothing is known about it by way of any particulars of events.

In the backdrop of the huge span of time that we are dealing here, the very origin of life on Earth is nothing more than a wink of eye. If we rewind the time in a slow motion, our life – human life – is a fleeting speck of this wink! And yet a period of one or two thousands looks enormous to us. This is the mystery of the story of this universe, our Earth and the debut of life on this Earth.

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