Figure 1. The Helix Nebula; the gaseous outer layers expelled by a dying star. The ejected material enriches the interstellar medium (from which new stars and planets form) with carbon. Credit: NASA, ESA, C. R. O’Dell (Vanderbilt University), M. Meixner and P. McCullough (STScI).
Observations from the ground and with the Hubble Space Telescope have shown that the cosmic rate of birth of new stars reached its peak some 9–10 billion years ago, and it has been declining ever since. The peak in the universal rate of carbon production lags behind the cosmic star-formation rate by no more than about a billion years. Consequently, we can guess that if the universe did indeed experience a burst of life-formation, similar perhaps (in terms of its eruptive nature) to the Cambrian explosion on Earth, the earliest this might have happened was about 9 billion years ago.
It took life on Earth about three billion years to develop from primitive to complex. We have no idea if this is “typical,” but it seems reasonable to assume that if “intelligent” life develops at all, this process should take a few billion years, given the rather slow pace of Darwinian-like evolution. This means that we might expect “intelligent” (more cautiously, “complex”) life forms to have emerged in abundance in the universe some 5–6 billion years ago. If true, then there could be quite a few civilizations out there that are more advanced than ours by a few billions of years. How is that for a humbling thought?