By Josef Eisinger
In these troubled times, it is enlightening and consoling to ponder our place in the larger scheme of things. We are today privileged to have gained a realistic perspective of our place in the universe thanks to the great progress scientists have made in the past century. Their observations of the universe and the laws of nature they discovered explain the physical and biological evolution that brought humankind to the state it is in.
I find this insight most gratifying and it, in turn, raises the question posed in the title of this essay: Is our story of life on Earth unique or did life emerge on other planets scattered by the billions in our own galaxy, the Milky Way, and in the universe at large? And beyond that, did life elsewhere evolve to a technological state comparable to that attained on Earth—a notion that has some intrepid Earthlings contemplating interstellar communications.
The raw materials that make up a living organism—its constituent atoms and molecules—are at the base of all such speculations. We know from observations and the well-tested laws of physics that the same 92 stable nuclei that exist on Earth are also found in all reaches of our universe. We also know that, under suitable conditions, these positively-charged nuclei are surrounded by electrons to form atoms and molecules that interact with each other according to the laws chemistry—or, more precisely, according to the rules of quantum mechanics, which determine their affinities to each other. The results of many experiments give us confidence that the same physical laws are valid in all corners of our universe.
The raw materials of extra-terrestrial life—the elements and their chemistry—are therefore very familiar to us, whatever planet they find themselves on. But for a living organism to evolve from them, the prevailing conditions must be ‘just right,’ and must remain so for a very long time. We know that, under suitable conditions, the sun’s radiation can generate the basic building blocks of life (e.g., carbohydrates, amino acids) in water, although the crucial steps of assembling the components into a self-reproducing organism, remain hidden. The same chemical building blocks are, incidentally, also found in meteorites—those messengers from outer space that land on Earth.
All forms of life on Earth, from the lowly ant to the majestic whale, employ the same biological master plan to create a living organism: a genetic memory, coded with four letters (the bases of DNA), which is expressed in proteins that consist of some 20 different amino acids, strung together in the particular order that determines each protein’s form and function. Other schemes for generating living organisms may have existed on Earth in the distant past but could not compete with the formula outlined above; its remarkable stability and flexibility made Darwinian evolution possible.
While somewhat different biological schemes may well have evolved under different conditions, it seems likely that they would employ the same matchless solvent, water, and would also employ carbon-based molecules because the rules of quantum mechanics (Pauli Principle) endow the carbon atom with uncommon chemical versatility. In searching for extra-terrestrial life it is, in any case, reasonable to look where the prevailing conditions resemble those on Earth—home of the only example of a successful biological evolution we know.
In Part Two of this piece, I will further explore the nature of the conditions necessary to foster extraterrestrial life.
Josef Eisinger, Professor Emeritus at the Mount Sinai School of Medicine in New York, is the recipient of two Guggenheim Fellowships, and the author of more than 150 scholarly articles that range from nuclear physics and molecular biology to the history of science. While at Bell Laboratories, Eisinger’s research base for 30 years, he and colleagues developed the Hematofluorometer—a device for diagnosing lead poisoning. Eisinger is also the author of Einstein on the Road, Einstein at Home (Prometheus Books 2011, 2016) and his memoir, Flight and Refuge: Reminiscences of a Motley Youth (Amazon 2016).