IS THERE INTELLIGENT LIFE ON EARTH? 



PRESTON CLOUD 



Department of Geological Sciences, University of California, Santa Barbara, California 



This paper is about man's place on an evolving earth, about some of the 

 constraints that limit our choices in the occupancy of this earth, and about steps 

 that we might take to keep our options open. "The times, they are a-changin' " 

 says a well-known Bob Dylan song, and we are going to need bigger changes and 

 more of them before long. In a very deep sense, our times began "a-changin' " 

 with the insights of Copernicus, Kepler, Newton, and Darwin which brought 

 about man's dethronement from his position as the epitome and center of 

 creation and caused him to begin asking a lot of questions about himself and his 

 relation to the universe. Among the questions asked most frequently and most 

 persistently is the question: Is there life elsewhere in the universe? And, if so: 

 Might there even be intelligent life elsewhere, perhaps on some other planet to 

 which man might move after filling this one up? It is interesting in looking at 

 this question to turn it around and ask: What is the evidence for intelligent life 

 on Earth? 



Consider the views we have now seen of Earth from space. We can all see it 

 in our mind's eye— a tiny, fragile speck in the dark emptiness of space, 

 essentially a closed system. This is a picture of the earth that man in general has 

 never really grasped until recently, despite the warnings and the urgings of 

 generations of ecologists. Suppose now, to get things into perspective, that you 

 were an inhabitant of another planet, a planet with an atmosphere but without 

 free oxygen. Imagine that you had somehow managed to evolve into an 

 observing, reasoning being with an anaerobic metabolism. Assume further that in 

 the laboratories on your planet there had developed an understanding of the 

 origins of life comparable with that now existing on Earth and, in addition, that 

 spectroscopic and other remote sensing devices based on your planet have told 

 you that there is about 20% oxygen in Earth's atmosphere. You would conclude 

 that there could be no life on Earth — oxygen being poisonous to all forms of 



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