Q. Consider the following statements:
- The Earth’s magnetic field has reversed every few hundred thousand years.
- When the Earth was created more than 4000 million years ago, there was 54% oxygen and no carbon dioxide.
- When living organisms originated, they modified the early atmosphere of the Earth.
Which of the statements given above is/are correct?
- 1 only
- 2 and 3 only
- 1 and 3 only
- 1, 2 and 3
Answer: (c) 1 and 3 only
Notes
- Earth’s magnetic field
- On the scale of a million years, the earth’s magnetic fields has been found to reverse its direction.
- Scientists estimate reversals have happened at least hundreds of times over the past three billion years.
- Over the last 20 million years, magnetic north and south have flipped roughly every 200,000 to 300,000 years. The last of these major reversals occurred about 780,000 years ago.
- Early atmosphere
- Earth’s original atmosphere was rich in methane, ammonia, water vapour, and the noble gas neon, but it lacked free oxygen. It is likely that hundreds of millions of years separated the first biological production of oxygen by unicellular organisms and its eventual accumulation in the atmosphere.
- Between 4.5 and 2.5 billion years (the Archaean and Proterozoic time), the earliest secondary atmosphere contained carbon dioxide (CO2), methane (CH4), water vapor (H2O), carbon monoxide (CO), a little nitrogen (N), and hydrogen (H). So Carbon dioxide is present.
- When living organisms originated, they did not affect the early atmosphere. However, according to the official answer key, the answer is 1 and 3 only.
