Researchers Peter Behroozi and Molly Peeples, both of the Space Telescope Science Institute (STScI), used data from the Kepler and Hubble space telescopes to estimate Earth's position on the timeline of habitable world evolution. While the question of what form other life might take is a big philosophical quandary (read more on that here), most scientists agree we should look for life that looks like us: Something that formed on a rocky planet with the right size and star distance to host liquid water.
The researchers found that — while star formation has slowed down overall, and the Milky Way is running out of star-forming gas — most galaxies have so much star-making material left that they'll be able to keep churning out solar systems for a long time.
Based on Peeples and Behroozi's calculations, only about 8 percent of the planets of this type that the universe has the potential to create had been created when our own planet was born. That leaves a whopping 92 percent that are trailing behind us.
Considering the fact that it took hundreds of millions of years for the very simplest forms of life on Earth to show up, and another few billion years for us and our animal friends to evolve intelligence, there's a good chance that the brunt of potentially habitable worlds won't have their day until ours is long over.
Then again, there are already an estimated 1 billion rocky, Earth-sized planets in our galaxy alone, many of which may be in the habitable zones of their host stars. So even if the odds are bound to be better in a few trillion years, they're not so horrible today.