17 AUGUST 2006
Physics is the flashy science, the stuff of stars and galaxies, the stuff of quantum mysteries and black holes, the stuff of, well, stuff in general.
Chemistry, on the other hand, is the old stodgy science that doesn't make the news very much anymore, except for steroid abuse by athletes and pollution from toxic chemical spills.
But when you think about it, which is really more worthy of wonder? Physics may make the universe possible, but without chemistry such a universe would be a pretty dull -- specifically, lifeless -- place. It's not just that there's better living with chemistry -- there's no living without chemistry.
Physicists might argue that physics makes chemistry (and therefore life) possible. And it's true, physics provides the foundation. But chemistry builds the house. So it shouldn't be surprising that some scientists find the pursuit of primordial chemistry to be just as rewarding as tracking down bosons and gravity waves.
In fact, the search for the chemical origins of life has expanded its horizons dramatically in recent years. Decades ago, scientists struggled to decipher the chemical reactions necessary to initiate life in warm little ponds on the primitive Earth. Nowadays astrochemists scan the skies for signs from deep space that biochemistry was invented even before the Earth was born.
The Blue Marble (right) Credit: Visible Earth and NASA
OCEAN/STORMS, SUN (above) Credit: NASA Johnson Space Center - Earth Sciences and Image Analysis (NASA-JSC-ES&IA)
It now seems not too unlikely that the impetus for life's origin on Earth came from molecules born among the stars. After all, microfossils and other chemical evidence indicate that life appeared on Earth rather quickly after the baby planet cooled to habitable temperatures.
"The relatively short time interval," writes Harvard chemist William Klemperer, "suggests that terrestrial life may have required help from extraterrestrial chemistry."
Four decades ago, only a handful of simple molecules had been detected in the space between the stars. Today more than 130 have been detected, some of them as complex as those in the introductory chapters of organic chemistry textbooks. (You can see the list by clicking on Molecules in Space here.)
These molecules betray their identity by emitting (or blocking) specific colors of light or frequencies of other radiation. Each molecule affects precise frequencies, depending on the atoms it is made of and how they are connected. Earthbound chemists can measure the frequencies for known molecules in the lab and match them to the signals from space.
Figuring out how the biologically interesting molecules are produced in space is a hot topic these days. Some come about from reactions in the gaseous state of matter within interstellar gas clouds. More elaborate molecules appear to form in the hot cores of such clouds (hot by space standards -- still much colder than Wisconsin in January). In those regions molecules may attach themselves to grains of dust where more complicated chemistry is possible than gases alone allow.
Molecular birthplaces seem to be in the same locale as the maternity wards of stars, although there appear to be some differences in the molecules created near high-mass, as opposed to lightweight, stars.
Some experts believe the sun itself was born in the neighborhood of a much more massive star that formed in the hot core of a molecular cloud. If so, the chemistry in hot cores would be relevant to the chemistry of the solar system, as astronomer Lewis Snyder of the University of Illinois discusses in the current issue (August 15) of the Proceedings of the National Academy of Sciences.
That massive star would have exploded, peppering the area with chemicals from its birthplace, supplying our newborn solar system with the kind of molecules life could be built from. Delivering those molecules to their new home on Earth might have been accomplished by comets or asteroids, which bombarded the young planet for hundreds of millions of years after its birth.
"Grains in cometary nuclei may have carried prebiotic organic chemistry from the interstellar clouds to the early Earth," writes Snyder.
Among those molecules just might have been simple amino acids, the molecular building blocks of proteins. Astronomers have not yet confirmed the existence of an amino acid in space, but the simplest one, glycine, is a good possibility. Its molecular structural is similar to that of acetic acid, which has been detected in the hot cores of molecular clouds.
So studying the chemistry in such clouds may very well be a way of finding out what chemistry was like on the early Earth. Thoroughly understanding that chemistry would therefore take scientists a big step closer to answering the riddle of how life originated on the Earth to begin with.
It's another example of science finding a way to answer a question that seems at first glance unanswerable. Life on Earth began more than 3.5 billion years ago, a time supposedly too distant for scientists to reconstruct the steps leading up to it. But the universe is vast enough to maintain records of the past in all its various stages. Science can study the Earth's past by observing realms where similar "Earths" remain in the future.
Someday such studies may disclose the whole story of how life arises from lifelessness. And if it turns out that life's ingredients really did originate in the clouds of deep space, we can be more confident than ever that life, and probably chemists, exist throughout the cosmos.
E-mail: tsiegfried@nasw.org
