Carl Sagan on Nature

"The sky calls to us. If we do not destroy ourselves, we will one day venture to the stars."

"In the long run, the aggressive civilizations destroy themselves, almost always. It’s their nature. They can’t help it."

"Carbonaceous meteorites that fall to the Earth... have several percent to as much as 10 percent of complex organic matter in them."

"The price we pay for the anticipation of our future is anxiety about it. Foretelling disaster is probably not much fun; Pollyanna was much happier than Cassandra. But the Cassandric components of our nature are necessary for survival."

"Natural selection has served as a kind of intellectual sieve, producing brains and intelligences increasingly competent to deal with the laws of nature. This resonance, extracted by natural selection, between our brains and the universe may help explain a quandary set by Einstein: The most incomprehensible property of the universe, he said, is that it is so comprehensible."

"The Platonists and their Christian successors held the peculiar notion that the Earth was tainted and somehow nasty, while the heavens were perfect and divine. The fundamental idea that the Earth is a planet, that we are citizens of the Universe, was rejected and forgotten."

"At birth all of us imagine that we are the universe, and we don't distinguish the boundaries between ourselves and those around us. ...in some social situations, there is the sense that we are central, important. ...there was a natural projection of those attitudes upon the universe."

"That in nonarithmetic operations the small and slow human brain can still do so much better than the large and fast electronic computer is an impressive tribute to how cleverly the brain is packaged and programmed—features brought about, of course, by natural selection. Those who possessed poorly programmed brains eventually did not live long enough to reproduce."

"We embarked on our journey to the stars with a question first framed in the childhood of our species and in each generation asked anew with undiminished wonder: What are the stars? Exploration is in our nature. We began as wanderers, and we are wanderers still. We have lingered long enough on the shores of the cosmic ocean. We are ready at last to set sail for the stars."

"The amount of organic matter that could have been produced in the first few hundred million years of Earth history was sufficient to have produced in the present ocean a several-percent solution of organic matter. This is just about the dilution of Knorr's chicken soup, and not that different from the composition either. And chicken soup is widely known to be good for life."

"The entire recent history of biology shows that we are, to a remarkable degree, the results of the interactions of an extremely complex array of molecules; and the aspect of biology that was once considered its holy of holies, the nature of the genetic material, has now been fundamentally understood in terms of the chemistry of its constituent nucleic acids, DNA and RNA, and their operational agents, the proteins."

"Let's say there's a molecule that produces a religious experience... a natural molecule that the body produces whose function it is to produce religious experiences, at least on occasion? ...So let's call it "theophorin"...What could the selective advantage of theophorin be? ...to suit us for the quest that was, according to Dostoyevsky, to strive for nothing so incessantly and so painfully as to find someone to worship and obey."

"All my life, I've wondered about life beyond the earth. On those countless other planets that we think circle other suns, is there also life? Might the beings of other worlds resemble us, or would they be astonishingly different? What would they be made of? In the vast Milky Way galaxy, how common is what we call life? The nature of life on earth and the quest for life elsewhere are the two sides of the same question: the search for who we are."

"Let's go back to the solar nebula... with the temperature declining the farther we get from the Sun. ...at different distances from the Sun, different materials will condense out, because they have different vapor pressures or different melting points. ...water condenses out roughly at the vicinity of the Earth, whereas silicates condense out closer to the Sun... you have to go out to somewhere near the present distance of Saturn before methane condenses."

"We wish to pursue the truth no matter where it leads — but to find the truth, we need imagination and skepticism both. We will not be afraid to speculate, but we will be careful to distinguish speculation from fact. The cosmos is full beyond measure of elegant truths; of exquisite interrelationships; of the awesome machinery of nature. The surface of the Earth is the shore of the cosmic ocean. On this shore we've learned most of what we know. Recently we've waded a little way out, maybe ankle deep, and the water seems inviting. Some part of our being knows this is where we came from. We long to return. And we can. Because the cosmos is also within us. We're made of star-stuff. We are a way for the cosmos to know itself."

"There is no other species on the Earth that does science. It is, so far, entirely a human invention, evolved by natural selection in the cerebral cortex for one simple reason: it works. It is not perfect. It can be misused. It is only a tool. But it is by far the best tool we have, self-correcting, ongoing, applicable to everything. It has two rules. First: there are no sacred truths; all assumptions must be critically examined; arguments from authority are worthless. Second: whatever is inconsistent with the facts must be discarded or revised. We must understand the Cosmos as it is and not confuse how it is with how we wish it to be."

"There is a place with four suns in the sky — red, white, blue, and yellow; two of them are so close together that they touch, and star-stuff flows between them. I know of a world with a million moons. I know of a sun the size of the Earth — and made of diamond. There are atomic nuclei a few miles across which rotate thirty times a second. There are tiny grains between the stars, with the size and atomic composition of bacteria. There are stars leaving the Milky Way, and immense gas clouds falling into it. There are turbulent plasmas writhing with X- and gamma-rays and mighty stellar explosions. There are, perhaps, places which are outside our universe. The universe is vast and awesome, and for the first time we are becoming a part of it."

"Those who are skeptical about carbon dioxide greenhouse warming might profitably note the massive greenhouse effect on Venus. No one proposes that Venus's greenhouse effect derives from imprudent Venusians who burned too much coal, drove fuel-inefficient autos, and cut down their forests. My point is different. The climatological history of our planetary neighbor, an otherwise Earthlike planet on which the surface became hot enough to melt tin or lead, is worth considering — especially by those who say that the increasing greenhouse effect on Earth will be self-correcting, that we don't really have to worry about it, or that the greenhouse effect is a "hoax."

"The choice is with us still, but the civilization now in jeopardy is all humanity. As the ancient myth makers knew, we are children equally of the earth and the sky. In our tenure on this planet we've accumulated dangerous evolutionary baggage — propensities for aggression and ritual, submission to leaders, hostility to outsiders — all of which puts our survival in some doubt. But we've also acquired compassion for others, love for our children and desire to learn from history and experience, and a great soaring passionate intelligence — the clear tools for our continued survival and prosperity. Which aspects of our nature will prevail is uncertain, particularly when our visions and prospects are bound to one small part of the small planet Earth. But up there in the immensity of the Cosmos, an inescapable perspective awaits us. There are not yet any obvious signs of extraterrestrial intelligence and this makes us wonder whether civilizations like ours always rush implacably, headlong, toward self-destruction. National boundaries are not evident when we view the Earth from space. Fanatical ethnic or religious or national chauvinisms are a little difficult to maintain when we see our planet as a fragile blue crescent fading to become an inconspicuous point of light against the bastion and citadel of the stars. Travel is broadening."