While many environmentalists bemoan the amount of carbon belched into Earths atmosphere annually via fossil-fuels, what you will never see reported in the news is Mother Natures dirty little secret that is, natures own giant carbon footprint on the face of terra firma, in this case, the daily downpour of microscopic carbon molecules from space. Tens of tons of carbon molecules, in the form of dust particles and meteorites, rain down on the Earth every day yes, thats right: tens of tons of carbon fall to the Earth from space in just a single 24-hour period. I wonder if climate scientists factor this obscure fact into their annual atmospheric CO2 calculations? If not, it may be a case of scientists not talking to each other across lines of research specialties, a frequent concern among the sciences. The amount of carbon delivered to the Earth in a 24-hour period is staggering and its almost hard to believe at first. But using a very conservative mathematical formula that extrapolates such things, astronomers are now in agreement that theres a lot of carbon in space and a lot of it falls to Earth and on the other planets. Meteorites are the chief transporters of carbon molecules to Earth; these molecules are continually analyzed by researchers in the laboratory. Meteorite carbon typically comes in the form of polycyclic aromatic hydrocarbons (PAHs); they are stable compounds and survive the hot plunge through Earths thick atmosphere. PAHs are found in everything in our universe from stars to barbeque steaks, even automobile exhaust. If you look at these molecules under an electron microscope, their intricate structures will remind you of common, barnyard chicken wire. Most astronomers now believe that PAHs are created inside the thermonuclear furnaces of dying, giant red stars. These enormous stars appear very rich in the element carbon; these stars help seed the universe with a major constituent of the building block of life on Earth and probably elsewhere. Using infrared spectroscopy, a team of scientists at the NASA Ames Research Center in California recently proved that hydrocarbon molecules produced by automobiles and created artificially in the lab are the spitting image of carbon molecules found in meteorites and observed in deep space. Certain PAH molecules, called quinones, are also found in all lifeforms on Earth. So the building blocks of life are found not only in meteorites, but they are also found in automobile exhaust. To paraphrase the popular Walt Disney World tune, Its a small universe after all. You may recall that PAHs were detected in the famous (or shall I say infamous?) 1996 Mars meteorite that created a media firestorm over possible fossil martian life signs. Molecules from space helped to make the Earth the pleasant place that it is today, said Louis Allamandola of the NASA Ames Astrochemistry Laboratory. We now understand why these life-like carbon compounds are raining down on the Earth and other planets. Knowing this will help us search for life on other worlds... Whats in the Sky: The night of Friday, Oct. 10, will afford a fun glimpse of a several beautiful, bright stars. Go outside around 9 p.m.; youll see the stars Fomalhaut (bright white) in the southeast, Capella (yellow) in the northeast. The stars Deneb, Vega, and Altair are high overhead. Lou Varricchio, M.Sc., is a former NASA science writer and Public Radio International science reporter. He is currently involved with the NASA/JPL Solar System Ambassador program in Vermont where he speaks to schools and civic groups about space exploration.