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FUNDAMENTALS OF PHYSICAL GEOGRAPHY 12
THE EARTH
This unit deals with
? Origin and evolution of the earth; Interior of the earth; Wegener’s
continental drift theory and plate tectonics; earthquakes and
volcanoes
UNIT
II
2024-25
Page 2


FUNDAMENTALS OF PHYSICAL GEOGRAPHY 12
THE EARTH
This unit deals with
? Origin and evolution of the earth; Interior of the earth; Wegener’s
continental drift theory and plate tectonics; earthquakes and
volcanoes
UNIT
II
2024-25
D
o you remember the nursery rhyme
“…Twinkle, twinkle little star…”?
Starry nights have always attracted us since
the childhood. You may also have thought of
these stars and had numerous questions in
your mind. Questions such as how many stars
are there in the sky? How did they come into
existence? Can one reach the end of the sky?
May be many more such questions are still
there in your mind. In this chapter, you will
learn how these “twinkling little stars” were
formed. With that you will eventually also read
the story of origin and evolution of the earth.
EARLY THEORIES
Origin of the Earth
A large number of hypotheses were put forth
by different philosophers and scientists
regarding the origin of the earth. One of the
earlier and popular arguments was by German
philosopher Immanuel Kant. Mathematician
Laplace revised it in 1796. It is known as
Nebular Hypothesis. The hypothesis considered
that the planets were formed out of a cloud of
material associated with a youthful sun, which
was slowly rotating. In 1950, Otto Schmidt in
Russia and Carl Weizascar in Germany
somewhat revised the ‘nebular hypothesis’,
though differing in details. They considered that
the sun was surrounded by solar nebula
containing mostly the hydrogen and helium
along with what may be termed as dust. The
friction and collision of particles led to formation
of a disk-shaped cloud and the planets were
THE ORIGIN AND EVOLUTION
OF THE EARTH
CHAPTER
formed through the process of accretion.
However, scientists in later period took up
the problems of origin of universe rather than
that of just the earth or the planets.
MODERN THEORIES
Origin of the Universe
The most popular argument regarding the origin
of the universe is the Big Bang Theory. It is also
called expanding universe hypothesis. Edwin
Hubble, in 1920, provided evidence that the
universe is expanding. As time passes, galaxies
move further and further apart. You can
experiment and find what does the expanding
universe mean. Take a balloon and mark some
points on it to represent the galaxies. Now, if
you start inflating the balloon, the points marked
on the balloon will appear to be moving away
from each other as the balloon expands.
Similarly, the distance between the galaxies is
also found to be increasing and thereby, the
universe is considered to be expanding.
However, you will find that besides the increase
in the distances between the points on the
balloon, the points themselves are expanding.
This is not in accordance with the fact. Scientists
believe that though the space between the
galaxies is increasing, observations do not
support the expansion of galaxies. So, the
balloon example is only partially correct.
The Big Bang Theory considers the
following stages in the development of the
universe.
(i) In the beginning, all matter forming the
universe existed in one place in the form
of a “tiny ball” (singular atom) with an
2024-25
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FAQs on NCERT Textbook - The Origin and Evolution of the Earth - Geography for UPSC CSE

1. What is the origin of the Earth?
Ans. The Earth is believed to have originated about 4.6 billion years ago from a cloud of gas and dust called the solar nebula. Over time, this nebula collapsed under its own gravity, forming a spinning disk. The material in this disk eventually came together to form the Earth.
2. How did the Earth evolve over time?
Ans. The Earth has undergone several significant changes over its history. It initially had a molten surface due to intense heat from the formation process. As it cooled, a solid crust formed, and the first oceans appeared. Over millions of years, the Earth's atmosphere developed, allowing for the existence of life. Geological processes, such as plate tectonics and erosion, continue to shape the Earth's surface.
3. What evidence supports the theory of the Earth's evolution?
Ans. There is a wealth of evidence supporting the theory of the Earth's evolution. Fossil records provide evidence of the existence and extinction of various species over time. Geological formations, such as rock layers and sedimentary deposits, reveal the Earth's changing landscapes. Additionally, the study of isotopes in rocks and minerals helps determine their ages, providing further evidence of the Earth's long history.
4. How did life originate on Earth?
Ans. The exact origins of life on Earth are still being researched, but one prominent theory is that life originated from simple organic molecules in Earth's early oceans. These molecules gradually combined and evolved into more complex structures, eventually leading to the development of single-celled organisms. Over millions of years, these organisms diversified and evolved into the vast array of species we see today.
5. How has the Earth's climate changed over time?
Ans. The Earth's climate has undergone significant changes over its history. There have been periods of extreme cold, known as ice ages, as well as periods of warmer climates. These changes are primarily attributed to natural factors such as variations in the Earth's orbit and volcanic activity. However, human activities, particularly the burning of fossil fuels, have accelerated climate change in recent centuries, leading to concerns about global warming and its impacts.
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