For most of history, people thought the sky was unchanging and life was as it had always been. Many believed the Earth was the center of the universe and that humans were in some way "higher" than all other creatures. Then along came the Copernican revolution four centuries ago, and suddenly Earth shifted out of the center of the universe to take up its true position among the planets in our solar system. About two and a half centuries later, another revolution took place when Charles Darwin revealed the true relation between humans and all other life on Earth. These revolutions are similar for the way they shift perspective, and better inform us about our origins and our future.

We now know that everything changes. In four and a half billion years the Earth changed from a hot, dry, cratered rock to a temperate, ocean-dominated world teeming with life. We also know that most of the life that ever existed on Earth has gone extinct. The way that life changes, new species arising while others disappear, only makes sense thanks to Darwin and his theory of evolution. A perspective on how things change over time is also useful in astronomy.

When we look beyond the Earth, into deep space, we look back in history and we see that the universe and its contents change with time. The universe of 13.7 billion years ago has no stars, no planets, and no life of any kind. The universe was very simple then, composed only of hydrogen and helium. Slowly, clouds of these two gasses collapsed to form stars and the universe began to evolve. Stars, you see, are thermonuclear factories forming larger atoms from smaller ones. Primarily, hydrogen converts into helium, in the process releasing energy, which keeps the star from collapsing under its own gravity. Heavier stars can form larger atoms like carbon, nitrogen, and oxygen. Eventually, a star runs out of material for its nuclear furnace and it "dies". In that process, the star ejects, sometimes in a spectacular explosion, a fraction of its mass into space. The matter released by the star at death differs from the material forming the star at its birth. The ejected material is rich in heavier elements.

As new generations of stars form from the "evolved" remains of the old, the content of the universe begins to change. Rocky planets form. Simple molecules like water form and collect on the surfaces of these planets. The Earth formed after eight billion years, and the deaths of countless stars. On our young rocky planet, some interesting chemistry began. Scientists debate among themselves about the origins of life on the Earth. The exact mechanism and the location of Earths "cradle of life" remain for now shrouded in mystery. We do know, however, that the process began with the birth of the universe itself and passed through fusion fire in the hearts of giant stars.

As Carl Sagan said, we are made of "star stuff". We are one result of a process of Cosmic Evolution. There is nothing particularly exceptional about the Earth. The physical and chemical processes that happened here can happen anywhere in the universe. Our modern understanding of the processes driving astronomical and biological evolution gives SETI astronomers great optimism. If intelligence evolved here, it can evolve elsewhere, and we have the technology to find it if our analogues are exploiting the electromagnetic spectrum to communicate as we do.

Spending the 195^th anniversary of Darwins birth on the grounds of the Arecibo Observatory, I find myself contemplating such things as spider webs, nebulae and the process of contemplation itself. From all of us who carry human voyages of exploration into the cosmos, Happy Birthday, Charles!