Some 542 million years ago, life on Earth began to evolve and diversify from literal primordial slime that had existed for close to a billion years, and change in a radically sudden way. This would lead to the eventuality of more complex life forms and, of course, human beings a bit further on down the road.
But one thing we know about life on Earth today and, more importantly, in the far distant future, is that it simply cannot continue on existing as it has for the last several hundreds of millions of years. The warming influence of our Sun will eventually swallow the habitability of life on this planet, and by then, we will either be forced to use science to escape this problem, or we too shall fall before the very elements of nature in the cosmos that once were responsible for life on Earth.
In addition to the existential problems we face, there are many who are equally concerned about the way that the lasting legacy of humankind may be represented for future generations of space travelers; perhaps travelers not of this world, but those arriving from distant star systems who would discover evidence of life that once existed on a barren planet we call Earth. If aliens were ever to arrive in search of life like us, what will we have left behind that they might discover?
Ever since the space probes Pioneers 10 and 11 were sent into space in 1972, NASA had been playing with the idea of sending simple "calling cards" so that alien beings who might one day discover these devices could learn something about who built them, and where they were from. Each of the Pioneer craft were fitted with a small metal plaque which contained details about Earth, which were kept rather simply to a summary of the date of their creation, and where they were from. The simplicity of such messages would change with the launch of Voyager, which contained what NASA describes as "a kind of time capsule, intended to communicate a story of our world to extraterrestrials." While the technology employed then would be considered rather dated today, the idea was novel; Voyagers 1 and 2 contained a gold-plated phonograph record featuring diagrams, sounds and images detailing what constitutes our way of life on Earth:
The contents of the record were selected for NASA by a committee chaired by Carl Sagan of Cornell University, et. al. Dr. Sagan and his associates assembled 115 images and a variety of natural sounds, such as those made by surf, wind and thunder, birds, whales, and other animals. To this they added musical selections from different cultures and eras, and spoken greetings from Earth-people in fifty-five languages, and printed messages from President Carter and U.N. Secretary General Waldheim. Each record is encased in a protective aluminum jacket, together with a cartridge and a needle. Instructions, in symbolic language, explain the origin of the spacecraft and indicate how the record is to be played.
The Voyager and Pioneer messages weren't the only attempts at contacting extraterrestrials. A similar message was sent via frequency modulated radio waves in November of 1974 from the Arecibo radio telescope in Puerto Rico. However, since the message would take 25,000 years to reach its destination in the globular star cluster known as M13, the arrangement of those stars will likely no longer be as they were when the message was fired; researchers involved with the project were aware of this, of course, including Frank Drake and Carl Sagan, who developed the contents of the "message." However, more than an actual letter to ET, the message was intended as a display of the capabilities of the technology available at that time.
There is always the possibility that, rather than sending proof of Earth life out into the cosmos, we might leave a sort of "time capsule" that could be found here in the distant future, perhaps as evidence of life that once existed, upon its discovery in a post-human world. Artist Trevor Paglen designed such a capsule, which consisted of 100 black and white images stored aboard a satellite designed for future discovery:
Billions of years from now, when the earth has erased all trace of our inhabitance, hundreds of dead satellites orbiting the planet will remain, immune to the terrestrial effects of rust, erosion, and decay -- the last artifacts left to say "we were here." A dubious bequest, perhaps. But for Paglen that ring of future space junk seemed the obvious place to put a public art installation: an archive of 100 black-and-white photographic images, built to last for billions of years, launched aboard a communications satellite into outer space from a site in Kazakhstan last week.
Perhaps one day Paglen's artistic contributions (which in the past have included some rather interesting examinations of the world of black or "invisible" elements of covert ops and agencies) will be represented among the sorts of testaments to human life on Earth that future space travelers will come across. But by that time, who knows really how much of the human experience may have been documented, preserved, or in likelihood, carried off with us into our ever-expanding universe on a mission toward furthering humankind's own expansion of limitations.