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Skywatching

Panspermia: life on earth originated from outer space

It came from outer space

The only planet known to bear life is ours. We are looking hard for evidence of life in our solar system, and on planets orbiting other stars that are suitable for life as we know it. The big question is whether the processes that led to life on Earth happened elsewhere. What is the chance of that?

We know that the clouds of gas and dust between the stars are loaded with the chemical raw materials for life. When each new planet forms it gets a ration of them. However, if the planet is too hot the chemicals are broken down, and if it is too cold they freeze solid, and nothing further happens. We also know that under the right conditions these chemicals can react together to form aminoacids, which are the building blocks for making proteins, the engines of life as we know it. However, it is a long way from aminoacids to proteins. How did very simple ingredients combine to produce such complex molecules without living things being there beforehand to make it happen?

Every day we see the processes by which Mother Nature breaks complicated things down into simple ones. Rain and temperature changes erode rocks and degrade minerals. Plant matter and dead animals get broken down into simple chemicals in the soil, which then become new living things. Going from simple things to complicated things is another issue. It takes a tremendous amount of energy and very special circumstances. It is also very energy inefficient. The energy that winds up incorporated into the complex structures is only a fraction of the energy needed to make them. What circumstances led to the formation of the first complex organic molecules? How likely are they to happen on a young planet? One idea that has been bouncing around the scientific community for years now is that maybe life appeared on just a few planets, or even one, and then it spread. This idea has come to be known as "panspermia."

A few years ago a bit of rock that had been knocked off Mars by a meteoric impact and had found its way to Earth after a journey of millions of years, was found to contain fossils of what looked like primitive live forms. It is now doubtful they were actually fossils of living things, but it once again raised the idea that involuntary passengers might be sent off on cosmic journeys to other worlds. Primitive life forms can remain dormant for really long periods of time in hostile conditions. We know that bacteria from Earth can survive on the moon for years, and those long distance travellers would be far more primitive life forms than modern bacteria. These immigrants finding themselves on new worlds with suitable conditions and a supply of suitable chemicals could seed a community of new living things, which would evolve to suit their own unique environment. After a few billion years, each world would have its own unique biosphere. Each new life-bearing world will have chunks knocked off it by cosmic impacts, launching an ever-increasing population of emigrants out there looking for new places to settle down.

Our planet formed around 4.5 billion years ago. It is interesting that traces of living things have been found in rocks between 3.3 and 3.5 billion years old. It seems as though life got going as soon as the young Earth had cooled enough for oceans to form. However, this life remained very simple for a long time. About 550 million years ago, life suddenly exploded in sophistication and diversity. During that period of almost 3 billion years where life stayed simple – maybe it was settling in – there were periods of intense meteoric bombardment. It is pretty certain that many bits were knocked off our world during that time, and possibly, in some cases, carrying off more involuntary emigrants on very long journeys to new worlds.

  • Before dawn, Jupiter and Saturn are close together in the south and Mars in the southeast.
  • The moon will reach last quarter on the 12th.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.



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About the Author

Ken Tapping is an astronomer born in the U.K. He has been with the National Research Council since 1975 and moved to the Okanagan in 1990.  

He plays guitar with a couple of local jazz bands and has written weekly astronomy articles since 1992. 

Tapping has a doctorate from the University of Utrecht in The Netherlands.

[email protected]



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The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

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