Question

Why was the primitive atmosphere of earth more beneficial to the origin of life than the modern atmosphere of earth?

• A. The primitive atmosphere was a reducing one that facilitated the formation of complex substances from simple molecules.
• B. The primitive atmosphere had a layer of ozone that shielded the first delicate cells.
• C. The primitive atmosphere was an oxidising one that facilitated the formation of complex substances from simple molecules.
• D. The primitive atmosphere had less free energy than the modem atmosphere, and thus newly formed organisms were less likely to be destroyed.

Answer 1

Answer: (A)

The correct option is B The primitive atmosphere was a reducing one that facilitated the formation of complex substances from simple molecules.
The primitive atmosphere of earth was reducing atmosphere with little or no oxygen but was rich in water vapour, carbon monoxide, carbon dioxide, nitrogen, and hydrogen. The UV and gamma radiations from Sun were the major sources of energy for chemogenesis as these radiations have energy quanta that can release electrons from atoms resulting in formation of highly reactive free radicals which in turn combined to form early organic compounds. The ozone layer of present day atmosphere absorbs these UV and gamma rays. Owing to immense long lasting rainstorms, tremendous amount of lightening was generated. Lightening provided energy for chemical reactions between hydrogen and free oxygen, nitrogen and carbon to form water (present in form of superheated steam due to high earth temperature), ammonia, methane and cyanides. The evolution of photoautotrophs from chemoautotrophs led to accumulation of oxygen in atmosphere and thus, ozone layer was formed much later during evolution. Thus, the correct answer is option B.