Extraterrestrial Civilizations - Isaac Asimov [78]
The key lay in that phrase long periods of time. The hit-or-miss random processes of evolution took a long time (even the evolutionists admitted that) and the question was whether there was time enough for the simple life form to be generated and all the myriad of complex life forms to be developed afterward
In Darwin’s time, scientists had abandoned the notion of a planet that was no more than 6,000 years old and spoke freely of Earth’s age as being in the millions of years, but even that didn’t seem long enough for evolution to do its work.
In the 1890s, however, radioactivity was discovered, and it was found that uranium turned to lead with almost stupefying slowness. Half of any sample of uranium would turn to lead only after 4,500,000,000 years. In 1905, the American chemist Bertram Borden Boltwood (1890–1927) suggested that the extent of the radioactive breakdown in rock would be an indication of the length of time since that rock had solidified.
Radioactive changes of all kinds have been used to measure the age of various parts of the Earth, of meteorites, and, recently, of Moon rocks, and the general consensus now is that the Earth, and the Solar system in general, is about 4,600,000,000 years old.
Hints of this vast age were already available in the early decades of the twentieth century, and it began to appear that there was enough time for evolution to do its work, if life could somehow start spontaneously.
But could that spontaneous start take place?
Unfortunately, by the time the extreme age of the Earth came to be understood, the extreme complexity of life also came to be understood, and the chance of spontaneous generation seemed to shrink further.
Twentieth-century chemists learned that protein molecules, which are molecules peculiarly characteristic of life, were made up of long chains of simpler building blocks called amino acids. They found that every protein had to have every one of thousands of different atoms (even millions in some cases) placed just so if it was to do its work properly. Later on, they discovered that an even more fundamental type of molecule, those of the nucleic acids, were even more complicated than protein molecules. What’s more, different nucleic acids and different proteins, along with smaller molecules of all kinds, intermeshed in complicated chains of reactions.
Life, even the apparently simple life of bacteria, was enormously more complicated than had been imagined in the days when the matter of spontaneous generation was being squabbled over. Even the simplest form of life imaginable would have to be built up out of proteins and nucleic acids, and how did those come to be formed out of dead matter? The origin of life on Earth, despite evolution, seemed more than ever a near-miraculous event.
Some scientists gave up and, in effect, washed their hands of the problem. The Swedish chemist Svante August Arrhenius (1859–1927) published a book, Worlds in the Making, in 1908, which took up the matter of the origin of life. In the book, Arrhenius upheld the universality of life and suggested that it was a common phenomenon in the Universe.
He went on to suggest that life might be, in effect, contagious. When simple living things on Earth form spores, the wind carries them through the air to burgeon in new places. Some by the blind force of the wind might be wafted upward high into the atmosphere and actually, Arrhenius speculated, out into space. There they might drift for millions of years through vacuum, pushed by the Sun’s radiation, protected by a hard, impervious pellicle and fiercely retaining the spark of life inside. Eventually, a spore would encounter some suitable planet without life and from it life would start on that planet.
In fact, Arrhenius suggested, that was how life on Earth got its start. It was vitalized by spores from space; spores that had originated on some other world that might remain forever unidentified.
Several points can be used to argue against this notion. One can calculate how many