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

1. Correct. Geological evidence shows the Earth's magnetic field has undergone many reversals, typically over intervals of a few hundred thousand years on average, though not at fixed intervals.

2. Incorrect. The early Earth’s atmosphere did not have 54% oxygen; free oxygen was almost absent initially, while gases like carbon dioxide, water vapour, methane and ammonia were present.

3. Correct. Early living organisms, especially photosynthetic microbes like cyanobacteria, gradually altered the atmosphere by releasing oxygen.

So, statements 1 and 3 only are correct.