The recipe for life

Ken Tapping, June 19, 2013

In the sky this week…

  • On 20 June the Sun reaches the northernmost point in its annual path around the sky, marking the summer solstice.
  • Venus and Mercury lie close together in the sunset twilight. Saturn is high in the southern sky.
  • The Moon will be Full on the 23rd.

On occasion something big slams into our planet. Perhaps the best known is the impact that happened sixty five million years ago, and which contributed to the extinction of three-quarters of the species living on Earth at the time. More recently, in 1908, a much smaller cosmic object exploded over Tunguska, Siberia, where it flattened trees for miles and rattled glasses in bars in Paris, thousands of kilometres away. We have been hit many times in our history, and will certainly be hit again in future.

We can divide the bodies wandering around the Solar System and which occasionally hit us into two broad classes. There are asteroids, which are lumps of rocky material ranging in size from gravel-sized particles up to bodies a thousand kilometres in diameter, and comets, large lumps of dirty ice that can be many kilometres in size. The Tunguska object was almost certainly a comet, and it has been suggested it might have been a much larger comet that hit us 65 million years ago. It is regarded that being hit by an asteroid or comet is not a good thing. However, without those impacts we would not be here. The story starts in the Milky Way.

These evenings the Milky Way spans the sky like a great arch, from the northeastern horizon and then down into the south. Binoculars will show the silvery stream to be made up of countless faint stars. We also see great dark lanes and patches that appear to split the stream. These are great clouds of cold gas and dust. They contain the elements produced as waste products from energy production in stars, and which have been quietly pickling for millions of years, forming a mixture of organic chemicals that are the building blocks for life as we know it.

New planets form from the collapse of these clouds. The material coagulates into bigger and bigger lumps, which grow by crashing into one another. However, these collisions liberate a lot of heat, and the young planets are huge balls of molten rock. Any organic chemicals would be incinerated. That is how our Earth was formed, 4.5 billion years ago.

These collisions would have involved both asteroids and comets. The asteroids provided building materials for the new planet. The comets contributed water, loaded with all those organic chemicals. They probably provided most of the water in our oceans and added the raw materials that made the beginning of life possible.

Observations show that to a large degree the chemical concoctions we see in those dark gas and dust clouds do not vary much across our galaxy and probably are much the same in other galaxies. This suggests that whenever the conditions on a planet are right, life is likely to arise, and since it comes from the same chemical recipe, based on carbon, the basic chemistry of life should be similar. However, that does not mean alien life forms need look anything like us. It is possible we might not even recognize them as something alive. After all we share our world with some very exotic creatures. For example, have you ever seen a sea cucumber? It takes a long hard look to confirm that it is a living creature.

Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astrophysical Observatory, Penticton, BC, V2A 6J9.

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