Question

How old is earth (in million years)?

• A. $3600$
• B. $4600$
• C. $7200$
• D. $6000$

Answer 1

The correct option is B $4600$

Solar system was born around 4600 million years ago by collapsing of gaseous cloud called as solar nebula under influence of its own force of gravity. It produced several cold, spinning and cloudy masses of cosmic dust and gases which are termed as nebulae. The central mass of nebula formed Sun which got hotter by conversion of its gravitational energy into heat. The rotational movement of nebula separated a ring of cloud which condensed into planets. Thus, Earth was originated around 4600 million years ago by condensation of cloud of dust and rocks surrounding the Sun.

The organisms that use light as source of energy and carbon dioxide as chief carbon source are referred to as photoautotrophic organisms. These photoautotrophs use water as electron donor during photophosphorylation that results in production of oxygen. The first photoautotrophs were Cyanobacteria like organisms which originated around 3600 million years ago as proved by fossil records.

Therefore, the correct answer is option B.