Explanation

In 1953, Stanley Miller and Harold Ureysynthesized amino acids by passing an electric discharge in a mixture of methane $\left( CH_{4} \right),\ ammonia\ \left( NH_{3} \right),\ hydrogen\left( H_{2} \right)and\ water\ vapours\ \left( H_{2}O \right).$ $\mathbf{Carbon\ dioxide}\left( CO_{2} \right)$was not present in the Urey-Miller experiment mixture.