27. 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?
(a) 1 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3
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?
(a) 1 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3
Explanation:-
- Statement 1: Reversal of Earth‘s magnetic field is called Geomagnetic reversal. It occurs every few million years. It is a change in a planet's magnetic field such that the positions of magnetic north and magnetic south are interchanged, while geographic north and geographic south remain the same.Thus, this statement is correct.
- Statement 2: Early atmosphere has an abundance of hydrogen sulphide and Carbon dioxide. There were smaller proportions of water vapour, ammonia and methane. The present composition got finalized very late – around 600 million years ago (Cambrian Period). Vulcanism and the very evolution of life played important roles in changing the atmospheric composition. Thus, this statement is incorrect.
- Statement 3: Respiration and microbial action by living organisms modified the early atmosphere. Thus, this option is correct.
- Option C is the most appropriate.
The Earth’s Magnetic field has reversed every few hundred thousand
years. This has been proved through Sea-Floor spreading.
When Earth was created there was no oxygen in the atmosphere. Oxygen makes up
about one-fifth the volume of Earth’¬s atmosphere today and is a central
element of life as we know it. But that wasn’¬t always the case. Oxygen,
although always present in compounds in Earth’¬s interior, atmosphere, and
oceans, did not begin to accumulate in the atmosphere as oxygen gas (O2) until
well into the planet’¬s history.
Carbon dioxide, water vapor, and methane played an important role in Earth’¬s subsequent development.
By 2.7 billion years ago, a new kind of life had established itself: photosynthetic microbes called cyanobacteria, which were capable of using the Sun’¬s energy to convert carbon dioxide and water into food with oxygen gas as a waste product. They lived in shallow seas, protected from full exposure to the Sun’¬s harmful radiation.
These organisms became so abundant that by 2.4 billion years ago the free oxygen they produced began to accumulate in the atmosphere.
Carbon dioxide, water vapor, and methane played an important role in Earth’¬s subsequent development.
By 2.7 billion years ago, a new kind of life had established itself: photosynthetic microbes called cyanobacteria, which were capable of using the Sun’¬s energy to convert carbon dioxide and water into food with oxygen gas as a waste product. They lived in shallow seas, protected from full exposure to the Sun’¬s harmful radiation.
These organisms became so abundant that by 2.4 billion years ago the free oxygen they produced began to accumulate in the atmosphere.