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Environmental Science: Origin of Earth: The Unique Planet Which Sustain Life

The universe is about 15 to 20 billion years old. The age of earth is approx. 4 - 5 billion years, while human beings evolved only around 2 million years ago.

Earth as Part of the Universe & Solar System

The Sun is a star. It is the star nearest to the earth about 150 million kilometers away. A Solar System consist of a star in the middle with a few planets orbiting around it. The earth is part of this system. Pluto is no longer regarded as a planet of earth՚s solar system.

Origin of the Universe and the Earth

  • ‘BIG BANG’ theory is widely accepted. According to this theory, universe started with a huge explosion and matter filled the entire space then dust and gases began to spin, as it spun faster and faster the center became very hot and it became the Sun. From the edges of this ball of dust and gas, big chunks of dust broke off and formed 8 ball shaped planets. Over a long period of time, dust and gas gradually condensed to form solid rock. With cooling of the crust hardened & formed the land, condensed water vapor into liquid water filling the depression to form seas.
  • The earth – with blue sky, vast ocean and lush green forests is the home to wide variety of organisms. At depth of about 8 km it is hot enough to roast a human body. About 32 km deep Mantle is present made up of hard rock. Core is 6400 km from the surface having temp. . Much of earth core is hot liquid.
  • Once every 24 hours, the earth rotates on its axis like a spinning top. The earth completes one full circle around the sun in days. Moon completes one orbit around earth in 27.33 days.
    Illustration: Origin of the Universe and the Earth

Earth- The Unique Planet Which Sustain Life

  • Conditions on the other seven planets of the solar system.
  • Mercury is the closest to the sun. Temp. Range of on side facing the Sun. It has no atmosphere.
  • Venus is about 40 mk away from the earth. Temp. . 96% carbon dioxide and poisonous gases like sulphur oxide and carbon monoxide.
  • Mars is called red planet. It has 95% carbon monoxide and reddish dust.
  • Jupiter is largest planet of solar system, clouds of ammonia and has no solid surface.
  • Saturn consist of hydrogen and helium. It is also made up of poisonous gas hydrogen cyanide.
  • Uranus has highly tilted rotational axis.
  • Neptune cold and dark with its surface coated with frozen methane.
  • Earth is the only planet known to sustain life.

Conditions Necessary for Sustaining Life

  • Presence of water because it is a universal solvent and life originate in water. 90% of cell content is also water.
  • Atmosphere consist of Nitrogen (78%) and oxygen (21%) small amount of carbon dioxide, water vapor, ozone and rare gases like argon, neon etc.
  • Average Temperature of the earth is
  • Buffering capacity of earth to maintain Ph 7
  • Earth gets light from the sun the ultimate source of energy.

Origin & Evolution of Life Prior to the Appearance of Human Beings

  • Gases of primitive atmosphere were primarily methane, ammonia, carbon dioxide and hydrogen there was no free oxygen.
  • Biological evolution from the simple organisms to complex organisms- as earth cooled, water vapour condensed to form liquid water. Rains poured to form water bodies on the earth. The molecules of life were formed in the water, evolved bacteria, the earliest and simplest organisms then different kind of bacteria which evolve green pigment chlorophyll which used carbon dioxide & water and released oxygen through photosynthesis and started accumulating in the atmosphere and transform reducing atmosphere into oxidising. At one-point oxygen content become 21% . This led to the invasion of land by living organisms.
  • Protists evolved from bacteria and both were unicellular then came multicellular and fungi followed by plants and animals. Today there are 5 kingdoms of life: Monera, Protista, Fungi, Plantae and Animalia.