We’ve seen that we share an atomic kinship with the cosmos, since the atoms that make up our bodies were churned out in the nuclear fires of stars. Here are some other ways in which we share an inextricable bond with events beyond our atmosphere:

1) cosmic rays contribute to evolution. Evolution depends upon genetic variation, and the ultimate source of genetic variation is mutation, which is a change in the DNA “letters”. Occasionally, such alterations result in a change in the product of a gene or in its level of expression that is beneficial to the organism harbouring that change. The mutation thus has an increased probability of being passed onto its offspring. This is known as natural selection: the non-random survival and reproductive success of individuals by virtue of their traits. Mutations can be caused by chemicals (called mutagens) or energy sources like radiation. Cosmic rays are put out by stars and are often comprised of protons, particles that are found within atoms but that become dissociated from them as a result of nuclear process in the cores of stars. UV (ultraviolet) rays and gamma rays are other examples of cosmic rays that can originate from extraterrestrial objects like stars and supernovas. When these reach Earth, they can contribute to mutations, some of which will be favoured by natural selection. Without mutations, evolution could never have gotten started, because evolution works on the raw material of variation in a population.

2) Meteorites contribute to mass extinction. Meteorites are pieces of rock and metal that pass through the Earth’s atmosphere. Most objects that enter the atmosphere (and this happens many, many times every day) burn up because of friction with molecules in the air. But sometimes, an object of some size can impact with the surface before being completely burned up. When this happens, it may release more energy than an atomic bomb. 65 million years ago, a meteorite impacted with the Earth and released many more times the energy of the world’s entire nuclear arsenal. This is thought to have ended the era of the dinosaurs (known as the Mesozoic Era, the “Age of the Reptiles”). While the details are controversial, and it now appears that many of the major divisions within the Mammalia had already evolved well before the K/T event, there can be little doubt that mass extinctions must have a significant influence on the tree of life and the avenues it will take. The largest mass extinction that ever occurred was the one that happened at the end of the Permian period 251 million years ago, which wiped out some 95 percent of all species living at the time. One estimate has it that over 99 percent of all the species that have ever existed are now extinct. To the extent that meteorites have influenced this pruning of the phylogeny of living forms, it makes sense to say that our very existence has therefore relied heavily upon events in the cosmos. If not for the mass extinctions of the past, we would likely not be here to talk about it. Perhaps some other intelligence might be here instead, or no intelligence at all.

3) Jupiter is a giant vacuum cleaner. The search for extraterrestrial life has conjured up some interesting questions about the sorts of conditions that must prevail not only on a planet capable of harbouring life, but in the solar system in which that planet resides. One of the prerequisites for life that has been proposed is for there to be a giant gas planet in the neighbourhood that soaks up most of the comets and asteroids before they can wreak havoc on the smaller, rockier worlds on which life can arise (at least life as we know it). A graphic illustration of this possibility was the Shoemaker Levy 9 impact in 1994, in which a giant comet went close to Jupiter, broke up, and was pulverised in its swirling clouds. If this comet had hit Earth, it would simply have wiped it out. So while extraterrestrial impacts have probably been important in contributing to our evolution, it would not do to have too many such impacts, because then the planet would be too inhospitable for any life to survive.

It seems that the more we learn about the cosmos, the more we find that there are deep, important connections between events happening out there and events that take place on our small world.