- 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?
(a) 1 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3
Answer: (c)
Statement 1 is correct:
The Earth’s magnetic field has flipped its polarity many times over the millennia. Reversals are the rule, not the exception. Earth has settled in the last 20 million years into a pattern of a pole reversal about every 200,000 to 300,000 years, although it has been more than twice that long since the last reversal. A reversal happens over hundreds or thousands of years, and it is not exactly a clean backflip. Magnetic fields morph and push and pull at one another, with multiple poles emerging at odd latitudes throughout the process. Scientists estimate reversals have happened at least hundreds of times over the past three billion years. And while reversals have happened more frequently in “recent” years, when dinosaurs walked Earth, a reversal was more likely to happen only about every few hundred thousand years. Earth’s polarity is not constant.
Statement 2 is not correct: When the Earth was created more than 4000 million years ago, it was a barren, rocky and hot object with a thin atmosphere of hydrogen and helium. Between 4,600 million years and the present, led to the evolution of life on the surface of the planet. The early atmosphere was probably mostly carbon dioxide, with little or no oxygen. There were smaller proportions of water vapour, ammonia, and methane. As the Earth cooled down, most of the water vapour condensed and formed the oceans.
Statement 3 is correct: There are three stages in the evolution of the present atmosphere. The first stage is marked by the loss of the primordial atmosphere. In the second stage, the hot interior of the earth contributed to the evolution of the atmosphere. Finally, the composition of the atmosphere was modified by the living world through the process of photosynthesis.
Elimination Technique: Statement 2 is fact loaded (i.e. 4000 million years ago, 54% oxygen and no carbon dioxide) which are vaguely mentioned. So, by eliminating the statement 2 ae are remaining with the option A and C only.
