Somehow, more than three billion years ago, living things appeared on Earth. That is only around a billion years after our planet formed, and it looks as though life got going here as soon as Earth had cooled down enough for liquid water to remain on its surface. However, how or what got it started remains unknown. Moreover, there are connections that make the question even more intriguing.
When the universe began it was almost completely made of hydrogen and helium. Stars formed from this and made all the other elements in the process of energy production during their lives, and in their death throes. These elements were accumulated into huge dust clouds in space that were dense enough to block ultraviolet from nearby stars and to become quite cold inside. Then, over millions of years, the elements started to react, forming chemical compounds important to the chemistry of life, such as water, ammonia, alcohol, formaldehyde, and a brew of various hydrocarbons. The elements also formed silica and minerals.
When planets formed, they did so from the material in these clouds. In the case of giant planets like Jupiter, located a long way from the Sun, these volatile chemicals were retained, forming deep, dense atmospheres. In a laboratory experiment, a mixture of these cosmic chemicals was put in a flask, and an electric discharge passed through it, simulating lightning. The result was a goop similarly coloured to the browns and other colours we see in Jupiterís atmosphere. Moreover, that goop was found to contain aminoacids, which are the building blocks of proteins and critical ingredients for life as we know it.
However, the Earth lies much closer to the Sun, and it is believed that the increased heat, combined with weaker gravity led to almost all that primordial atmosphere being lost. Since we live on a planet loaded with life, this raises a big question: where did the ingredients come from? One suggestion is that the impacts of fragments of planet-building material continued for a while after the Earth solidified, bringing in the chemicals needed to start the processes of life. This idea has been reinforced by the discovery of meteorites containing organic chemicals, including aminoacids.
Many organic molecules, including aminoacids can go together in two ways, one a mirror image of the other, referred to as left-handed and right-handed. When we make aminoacids in the lab, we get equal proportions of both versions. However, meteorites mostly contain the left-handed kind, which is what life here on Earth uses!
Discoveries like this suggest strongly that life here on Earth got jumpstarted by chemicals from space. That is interesting because it is likely that other planets received the same jumpstart ingredients. If that is the case we might expect our alien cousins to have somewhat similar body chemistries to ours, although it is very unlikely they will look anything like any living creature here on Earth.
Jupiter is low in the southwestern sky after sunset, setting about 7 pm. Saturn rises around 9 p.m., Venus rises about an hour before the Sun. The Moon will reach first quarter on the 12th.
Ken Tapping is an astronomer with the National Research Council’s Herzberg Institute of Astrophysics, and is based at the Dominion Radio Astrophysical Observatory, Penticton, B.C.