Important Questions: The Origin & Evolution of the Earth

Very Short Answer Type Questions

Q1: Who first proposed the Nebular hypothesis?
Ans: The Nebular hypothesis was first proposed by the German philosopher Immanuel Kant. Mathematician Laplace revised it in 1796.

Q2: Name all the nine planets in their order from the sun.
Ans: The document does not list the names of any planets. It only describes that planets formed through the process of accretion from a solar nebula containing mostly hydrogen and helium along with dust.

Q3: Name two scholars who had identical views on the origin of planets.
Ans: German philosopher Immanuel Kant and mathematician Laplace expressed similar views on the Nebular hypothesis.

Q4: Name the planet with a maximum number of satellites in our solar system.
Ans: The document does not mention any planet or the number of its satellites.

Q5: What are the various stages the sun has passed through during its formation?
Ans: The document does not describe stages such as nebula, supernova or protostar for the sun. It states that stars formed from a nebula 5-6 billion years ago through accumulation of hydrogen gas into clumps.

Q6: What is a meteorite?
Ans: The document does not discuss meteorites or meteors.

Q7: When did drifting start in Pangea?
Ans: The document does not mention Pangea or the drifting of continents.

Q8: Why does earth appear as a round ball that shines bright and blue when viewed from space?
Ans: The document does not describe the appearance of the earth from space.

Short Answer Type Questions

Q9: Explain Heterogenous Accretion Hypothesis.
Ans: The document does not mention the Heterogeneous Accretion Hypothesis. It describes planet formation in three stages: localised lumps of gas in a nebula develop a core and a rotating disc; the gas condenses into small rounded objects that become planetesimals by cohesion; and these planetesimals accrete to form planets. The layered structure later developed through differentiation.

Q10: What do you understand by a light-year?
Ans: A light-year is a measure of distance and not of time. Light travels at a speed of 300,000 km/second. The distance light travels in one year is taken to be one light-year. This equals 9.461 × 10¹² km. The mean distance between the sun and the earth is 149,598,000 km. In terms of light-years, it is 8.311 minutes.

Q11: What do you understand by the birth of the solar system?
Ans: The solar system formed from a solar nebula. The sun was surrounded by solar nebula containing mostly hydrogen and helium along with dust. Friction and collision of particles led to formation of a disk-shaped cloud. The planets were formed through the process of accretion.

Q12: Write a note on Heterogenous Accretion Hypothesis.
Ans: The document does not mention the Heterogeneous Accretion Hypothesis. It explains that planets formed by accretion of planetesimals and the earth developed a layered structure through differentiation, where heavier materials sank towards the centre and lighter ones moved towards the surface.

Long Answer Type Questions

Q15: Discuss the various hypotheses for the evolution of the planets.
Ans: Early theories proposed that planets formed out of a cloud of material associated with a youthful sun which was slowly rotating. This is known as the Nebular Hypothesis given by German philosopher Immanuel Kant and revised by mathematician Laplace in 1796. In 1950, Otto Schmidt in Russia and Carl Weizsäcker in Germany revised the Nebular Hypothesis. They considered that the sun was surrounded by solar nebula containing mostly hydrogen and helium along with dust. Friction and collision of particles led to formation of a disk-shaped cloud and the planets were formed through the process of accretion.
Later, scientists focused on the origin of the universe rather than just the planets. The most popular modern theory is the Big Bang Theory, also called expanding universe hypothesis. It considers that all matter existed in a tiny ball with infinite temperature and density. The tiny ball exploded 13.7 billion years ago leading to huge expansion. Within first three minutes atoms began to form. Within 300,000 years temperature dropped to 4,500 K and the universe became transparent.

Q16: Describe the origin of life and the cause for its origin.
Ans: Modern scientific ideas about the origin of life describe a gradual chemical evolution. Simple inorganic molecules combined under suitable conditions to form increasingly complex organic molecules. These organic molecules eventually organised into self-replicating systems, which marked the transition from non-living chemistry to living organisms. Evidence of early life is preserved as fossils in ancient rocks; structures similar to modern blue-green algae (cyanobacteria) have been found in rocks that are over three billion years old. Scientists estimate that life began to evolve on Earth roughly 3,800 million years ago. The early atmosphere and surface conditions were gradually altered by biological activity, which paved the way for more complex life forms.

Q17: Write short notes on: Origin of the Moon
Ans: During the formation of the moon, due to the giant impact, the earth was further heated up. It is through the process of differentiation that the earth-forming material got separated into different layers.

Q18: Describe the evolution of the Solar system.
Ans: The solar system formed from a solar nebula. The sun was surrounded by solar nebula containing mostly hydrogen and helium along with dust. Friction and collision of particles led to formation of a disk-shaped cloud. The planets were formed through the process of accretion in three stages. First, localised lumps of gas within a nebula developed a core and a huge rotating disc of gas and dust. In the next stage, the gas cloud condensed into small rounded objects which became planetesimals by cohesion. In the final stage, planetesimals accreted to form planets. This process is believed to have taken place about 4.6 billion years ago. Stars formed some 5-6 billion years ago.

Q19: Describe in short the evolution of atmosphere and hydrosphere (oceans).
Ans: There are three stages in the evolution of the present atmosphere. The first stage is marked by the loss of primordial atmosphere. The early atmosphere with hydrogen and helium was stripped off as a result of the solar winds. In the second stage, the hot interior of the earth contributed to the evolution of the atmosphere through degassing. Gases and water vapour were released from the interior. Continuous volcanic eruptions contributed water vapour and gases. The early atmosphere largely contained water vapour, nitrogen, carbon dioxide, methane and ammonia with very little free oxygen. As the earth cooled, water vapour condensed. Carbon dioxide dissolved in rainwater. Rainwater collected in depressions to give rise to oceans. The earth's oceans were formed within 500 million years from the formation of the earth. In the third stage, the composition of the atmosphere was modified by the living world through photosynthesis. Around 2,500-3,000 million years ago photosynthesis evolved. Oxygen began to flood the atmosphere 2,000 million years ago.

Q20: Describe in short the evolution of atmosphere and hydrosphere (oceans).
Ans: There are three stages in the evolution of the present atmosphere. The first stage is marked by the loss of primordial atmosphere rich in hydrogen and helium due to solar winds. In the second stage, degassing from the hot interior released water vapour, nitrogen, carbon dioxide, methane and ammonia. Volcanic eruptions added more gases. Cooling led to condensation of water vapour and formation of oceans within 500 million years. In the third stage, photosynthesis by living organisms around 2,500-3,000 million years ago produced oxygen. Oceans became saturated with oxygen and it began to flood the atmosphere about 2,000 million years ago. The oceans are as old as 4,000 million years. Life began to evolve around 3,800 million years ago.