15 short questions with answers on "The Origin and Evolution of the Earth," suitable for 2 to 3 marks each for Class 11 students.

1.Question: Briefly describe the Big Bang Theory.

Answer: The Big Bang Theory states that the universe originated from a single, incredibly hot and dense point about 13.7 billion years ago. This point underwent a massive expansion, leading to the formation of galaxies, stars, and planets as the universe cooled.

2.Question: What is the Nebular Hypothesis?

Answer: The Nebular Hypothesis proposes that our solar system formed from a rotating cloud of gas and dust called a nebula. Gravity caused the nebula to collapse and flatten into a disk, with the Sun forming at the center and planets accreting from the remaining material.

3.Question: Differentiate between terrestrial and gas giant planets.

Answer: Terrestrial planets (like Earth and Mars) are rocky and dense, located closer to the Sun. Gas giant planets (like Jupiter and Saturn) are large, have low densities, and are primarily composed of hydrogen and helium, located farther from the Sun.

4.Question: Explain the process of accretion in the formation of planets.

Answer: Accretion is the process by which smaller particles (dust and gas) in the protoplanetary disk collided and stuck together due to gravitational attraction and electrostatic forces. Over time, these aggregates grew larger, eventually forming planetesimals and then planets.

5.Question: What is planetary differentiation?

Answer: Planetary differentiation is the process by which a planet's interior separates into layers of different densities. For Earth, this resulted in a dense iron-nickel core, a silicate-rich mantle, and a lighter crust. This occurred due to the melting and sinking of heavier materials and the rising of lighter ones.

6.Question: Describe the Earth's early atmosphere.

Answer: Earth's early atmosphere was likely composed mainly of hydrogen and helium, which were stripped away by the solar wind due to the lack of a strong magnetic field initially.

7.Question: How did Earth's second atmosphere form?

Answer: Earth's second atmosphere formed primarily through volcanic outgassing, which released water vapor, carbon dioxide, nitrogen, and other gases from the planet's interior.

8.Question: What is the significance of the "Great Oxidation Event"?

Answer: The "Great Oxidation Event," which occurred billions of years ago, was a period when photosynthetic organisms (cyanobacteria) released significant amounts of oxygen into the atmosphere. This led to the formation of the ozone layer and paved the way for the evolution of aerobic life.

9.Question: What is radiometric dating and how is it used to determine the age of the Earth? Answer: Radiometric dating is a method used to determine the age of rocks and minerals by measuring the decay of long-lived radioactive isotopes. By analyzing the ratio of parent to daughter isotopes in ancient rocks, scientists have estimated the age of the Earth to be about 4.6 billion years.

10.Question: Name the four eons of the geological timescale.

Answer: The four eons of the geological timescale are the Hadean, Archean, Proterozoic, and Phanerozoic.

11.Question: Briefly explain the theory of plate tectonics.

Answer: The theory of plate tectonics states that the Earth's lithosphere is broken into several large and small plates that are constantly moving relative to each other. These movements are driven by convection currents in the mantle and result in phenomena like earthquakes, volcanoes, and mountain formation.

12.Question: What was Pangaea?

Answer: Pangaea was a supercontinent that existed approximately 300 million years ago, during the late Paleozoic and early Mesozoic eras. It comprised all the major landmasses of Earth joined together.

13.Question: What evidence supports the Big Bang Theory?

Answer: Key evidence supporting the Big Bang Theory includes the red shift of distant galaxies (indicating the universe is expanding) and the cosmic microwave background radiation (a remnant of the early, hot universe).

14.Question: How did the Earth's oceans likely form?

Answer: The Earth's oceans likely formed from the condensation of water vapor released during volcanic outgassing in the early atmosphere. As the Earth cooled, this water vapor condensed and accumulated in low-lying areas, forming the first oceans.

15.Question: What are the main layers of the Earth's interior?

Answer: The main layers of the Earth's interior are the crust (outermost solid layer), the mantle (thick, mostly solid layer), the outer core (liquid iron and nickel), and the inner core (solid iron and nickel).