From his experiments, S.L. Miller produced amino acids by mixing which of the following in a closed flask:

1. ${\mathrm{CH}}_3,$ ${\mathrm{H}}_2,$ ${\mathrm{NH}}_4$ $\mathrm{and}$ $\mathrm{water}$ $\mathrm{vapour}$ $\mathrm{at}$ $800°\mathrm{C}$

2. ${\mathrm{CH}}_4,$ ${\mathrm{H}}_2,$ ${\mathrm{NH}}_3$ $\mathrm{and}$ $\mathrm{water}$ $\mathrm{vapour}$ $\mathrm{at}$ $600°\mathrm{C}$

3. ${\mathrm{CH}}_3,$ ${\mathrm{H}}_2,$ ${\mathrm{NH}}_3$ $\mathrm{and}$ $\mathrm{water}$ $\mathrm{vapour}$ $\mathrm{at}$ $600°\mathrm{C}$

4. ${\mathrm{CH}}_4,$ ${\mathrm{H}}_2,$ ${\mathrm{NH}}_3$ $\mathrm{and}$ $\mathrm{water}$ $\mathrm{vapour}$ $\mathrm{at}$ $800°\mathrm{C}$

After about how many years of the formation of the earth, life appeared on this planet?

1. 500 billion years

2. 50 million years

3. 500 million years

4. 50 billion years