Passage II

The amino acid molecules necessary for life are thought to have been produced on Earth before organisms were present. Amino acids can be produced through chemical reactions among ammonia (NH₃), methane (CH₄), hydrogen (H₂), and water (H₂O). Four hypotheses have been proposed to describe the conditions that were responsible for the production of amino acids on Earth.

Hypothesis 1

Amino acids were introduced to Earth by meteors containing NH₃, CH₄, H₂, and H₂O. If the reactions among these 4 substances are provided enough energy, amino acids can be produced. As meteors containing these substances entered Earth’s atmosphere, the substances were rapidly heated by friction, and this heat resulted in immediate amino acid production on the surface of the meteors.

Hypothesis 2

Hypothesis 1 is correct that meteors brought NH₃, CH₄, H₂, and H₂O to Earth; however, amino acid production did not occur on the meteors. Once a meteor containing these substances entered Earth’s atmosphere, the substances were released into the atmosphere. Meteors continued to enter the atmosphere over hundreds of millions of years. The concentration of these substances in the atmosphere eventually became high enough for the reactions that produce amino acids to occur. The energy provided to these reactions was UV light energy from the sun.

Hypothesis 3

Meteors had nothing to do with the production of amino acids. Thermal vents (cracks in the floors of Earth’s oceans) allowed magma from Earth’s crust to seep into the ocean. The magma caused some of the ocean water to boil. Since ocean water contains dissolved NH₃, CH₄, and H₂, these substances were released into the atmosphere (along with H₂O) upon boiling. Then, UV light from the sun provided the energy for these substances to react to produce amino acids.

Hypothesis 4

Magma from thermal vents did not provide enough energy to cause ocean water to boil; however, the magma did provide enough energy to cause the NH₃, CH₄, and H₂ dissolved in ocean water to react with the ocean water, producing amino acids. These reactions occurred near the thermal vents.