UPSC Previous Year Question | Prelims GS | 2018

Consider the following statements: 1. The Earth's magnetic field has reversed every few hundred thousand years. 2. When the Earth was created more than 4000 million years ago, there was 54% oxygen and no carbon dioxide. 3. When living organisms originated, they modified the early atmosphere of the Earth. Which of the statements given above is/are correct?

  1. 1 only
  2. 2 and 3 only
  3. 1 and 3 only
  4. 1, 2 and 3

Answer

Correct Answer

1 and 3 only

Explanation

Geomagnetic reversals have occurred roughly every few hundred thousand years, and life (e.g. cyanobacteria) modified the early atmosphere by adding oxygen. Statement 2 is wrong: the early atmosphere had almost no free oxygen and did contain carbon dioxide.

Topics: earth's evolution and geomagnetism, geography, geomagnetic reversals and early atmosphere, physical geography