Recycled water vapour from the flask with heated water (represents Earth's early ocean) represented the rain. Those vapour supposed to be similar to the water evaporations from lakes and seas, before going into the atmosphere and forming the rain.
Apparatus also contained:
· mixture of gases similar to those found in Earth's early atmosphere, water (H2O), methane (CH4), ammonia (NH3) and hydrogen (H2) that were circulated inside a sterile array of glass tubes and flasks connected together in a loop.
· electrodes delivered an electric current which was simulating lightning
· the flask with heated water
