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17. The Earth in Space
Arnav Amol Karkare (7C)
Our planet seems very large and solid to us because we
are tiny compared to the vast universe. In reality, the Earth is
only a small heavenly body when seen in front of the universe. It
is just one planet in a system of planets, which we call the Solar
System.
The Sun, however, is only one of the many millions of
stars in a large system called a galaxy. In fact, when we look up
at the sky at night and see the stars of the Milky Way, we are
actually looking at our own galaxy. The Earth has a radius of a
little more than 6,000 kilometres, but our galaxy is about 80,000
light years across. What is even more amazing is that there are
millions of such galaxies in the universe.
Humans have always wondered how their planet came
into existence. Nowadays, cosmologists generally agree that the
universe was formed by what they call the Big Bang. Their idea
is that about 10,000 million years ago (10 billion years ago), a
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Adwait Devasthale (6A) Shubhra Deherkar (6A)
very dense mass of matter exploded and scattered, resulting in
the formation of galaxies.
From this universe, less than 9,000 million years ago, our
Solar System was formed. Scientists believe that there was a
huge cloud of dust and gas which, due to gravitational pull,
began to come together.
Around 4.5 billion years ago, this giant cloud of gas and
dust—called the solar nebula—collapsed under gravity. As it
collapsed, the nebula spun faster and faster, flattening into a disc
with the Sun at its centre. Particles in the disc began to stick
together, forming small bodies called planetesimals. These
collided and merged, growing into larger objects that eventually
formed the planets, including the Earth.
Intense heat and volcanic activity shaped the early Earth.
As the planet gradually cooled, water vapour condensed and
oceans were formed, paving the way for life to emerge.
Sanyukta Bhadbhade (7A) Rutvij Kamat (10C)