by Paul Braterman
It looks as if life on Earth just got older, and probably easier. Tiny scraps of carbon have been found inside 4.1 billion year old zircons, and examination shows that this carbon is most probably the result of biological activity. This beats the previous age record by 300 million years, and brings the known age of life on Earth that much closer to the age of Earth itself. The implication is that life can originate fairly quickly (on the geological timescale) when the conditions are right, increasing the probability that it will have originated many times at different places in our Universe.
The Solar System, it is now thought, formed when the shockwave from a nearby supernova explosion triggered a local increase in density in the interstellar gas cloud. This cloud was roughly three quarters hydrogen and one quarter helium, all left over from the Big Bang some 9 billion years earlier. It had already been seeded with heavier elements produced by red giant stars, to which was now added debris from the supernova, including both long-lived and short-lived radioactive elements. Once the cloud had achieved a high enough local density, it was bound to fall inwards under its own gravity, heating up as it did so. The central region of the cloud would eventually become hot enough and dense enough to allow the fusion of hydrogen to helium. A star was born.
The heavy elements (and in this context “heavy” means anything heavier than hydrogen and helium) in the dust cloud surrounding the nascent Sun gave rise to the rocky cores hidden within the outer giants Jupiter, Saturn, Neptune and Uranus, of the outer reaches of the Solar System, and to the rocky inner planets, Mercury, Venus, Mars, and, of course, to Earth and everything upon it. We are stardust.
The asteroids are made out of material that was never able to come together to form a planet, because of the competing gravitational pull of Jupiter. Asteroids are continually bumping into each other, scattering fragments, and some of these fragments fall to earth as meteorites. The Hubble Telescope has given usimages of star and planet formation in progress. Such is our modern creation myth, magnificent in scale, and rooted in reality.
