![]() In less dramatic versions of panspermia, microbes arrived on our planet via asteroids, comets or meteorites, or drifted down like confetti. This notion is called directed panspermia. Dissatisfied with conventional theories of life's beginning, Crick conjectured that aliens came to Earth in a spaceship and planted the seeds of life here billions of years ago. The most startling revelation in Overbye's article is that scientists have resuscitated a proposal once floated by Crick. The RNA world is so dissatisfying that some frustrated scientists are resorting to much more far out-literally-speculation. ![]() Overbye notes that "even if RNA did appear naturally, the odds that it would happen in the right sequence to drive Darwinian evolution seem small." Once RNA is synthesized, it can make new copies of itself only with a great deal of chemical coaxing from the scientist. RNA and its components are difficult to synthesize under the best of circumstances, in a laboratory, let alone under plausible prebiotic conditions. RNA could serve as gene and catalyst, egg and chicken.īut the "RNA-world" hypothesis remains problematic. If RNA could act as an enzyme, then it might be able to replicate itself without help from proteins. RNA, DNA's helpmate, remains the most popular answer to this conundrum, just as it was when I wrote "In the Beginning…" Certain forms of RNA can act as their own enzymes, snipping themselves in two and splicing themselves back together again. This fact turned the origin of life into a classic chicken-or-egg puzzle: Which came first, proteins or DNA? DNA can make neither proteins nor copies of itself without the help of catalytic proteins called enzymes. But there was a major hitch in this scenario. After Francis Crick and James Watson showed that DNA is the basis for genetic transmission in the 1950s, many researchers began to favor nucleic acids over proteins as the ur-molecules. But how exactly did chemistry first make the transition to biology?Īs recently as the middle of the 20th century, many scientists thought that the first organisms were made of self-replicating proteins. Researchers have found evidence of microbial life dating back 3.5 billion years ago, suggesting that life emerged fairly quickly-"like Athena springing from the head of Zeus," as one scientist quoted by Overbye put it. Geologists, chemists, astronomers and biologists are as stumped as ever by the riddle of life.Īfter its formation 4.5 billion years ago, Earth was bombarded for millions of years by huge meteorites, which would have wiped out any fledgling organisms. ![]() My editor nixed it, so we went with something less dramatic: "In the Beginning…: Scientists are having a hard time agreeing on when, where and-most important-how life first emerged on the earth." That editor is gone now, so I get to use my old headline, which is even more apt today.ĭennis Overbye just wrote a status report for The New York Times on research into life's origin, based on a conference on the topic at Arizona State University. Exactly 20 years ago, I wrote an article for Scientific American that, in draft form, had the headline above.
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