Life-giving manna really did descend from the heavens, but in the form of organic particles produced by photochemical reactions in Earth’s hazy atmosphere about 3.6 billion years ago. Laboratory simulations of Earth’s early atmosphere performed in the US suggest that the planet was showered with over 100 million tons of organic solids per year (PNAS 10.1073/pnas.0608561103). This may have occurred over millions or even billions of years, leading to speculation that these particles were involved in the formation of early life, and provided an abundant source of food for early life forms.
Margaret Tolbert and colleagues at the University of Colorado, Boulder subjected several mixtures of methane and carbon dioxide to ultraviolet radiation. These mixtures correspond to what scientists believe was the composition of Earth’s atmosphere at the time when life first appeared. Photochemical reactions in the mixtures produced a range of organic aerosols with an average diameter of about 50 nm. According to Tolbert, some of these particles could be consumed by organisms alive today.
“As these particles settle out of the skies, they would have provided a global source of food for living organisms”, speculated Colorado researcher Melissa Trainer. Previous theories on the origins of life focussed on specific environments such as thermal vents, where energy and nutrients are concentrated. A global and plentiful source of food, however, could have allowed life to spread much faster than previously thought. The smog-like haze created by the aerosols could also have shielded emerging life forms from harmful UV radiation.
