Are we alone?
This question has intrigued humanity for millennia. Hollywood has made billions of dollars producing movies that speculate on the answer. Philosophers and theologians have spent countless hours debating this very question. Even late-night talk show hosts and tabloid journalists have joined the game. Only for the last few decades have scientists been able to contribute any hard data; but the data they provide make a compelling case that Earth alone is designed to support life. Here are two recent examples.
Science Daily ran an article with a great headline, “The Aliens Are Silent because They’re Dead.” The title refers to Fermi’s Paradox. If, as some calculations show, the galaxy is teeming with alien societies, where are they? Why haven’t we seen them here on Earth or at least detected some signals from them in outer space? Scientists have proffered many answers. Perhaps Earth is a big zoo where these aliens observe us in an undetectable way. Maybe after a cost-benefit analysis, the aliens decided against colonizing the galaxy. The people claiming to see UFOs assert that aliens are visiting Earth, but Science Daily describes a more logical option.
Habitable Planets Need Life
From the moment life first appeared on Earth, it began altering the face of the planet. From changing the atmospheric oxygen and nitrogen, to enriching the oceans with nutrients and removing poisons, to recycling Earth’s biomass, life keeps Earth habitable. Now consider a recently formed habitable planet orbiting a star, and assume this planet actually hosts life. What would happen if that life did not change its environment quickly enough to counteract the dramatic astronomical and geological changes that occur on a young planet? The planet would experience runaway heating or cooling and any life would rapidly die.
It seems that many (if not all) exoplanets with hypothetical life could see that life snuffed out before it makes the planet sufficiently habitable. The scientists involved refer to this as a Gaian bottleneck.1 Such a scenario highlights Earth’s remarkable characteristics, which enable our world to support a diverse array of life 4.5 billion years after it formed.
Habitable Planets Need Rotations
Another possible scenario that would make advanced life rare (or unique to Earth) relates to the circadian rhythms (internal clocks) that govern our bodies. Studies show mice with circadian rhythms out of sync with Earth’s rotation have dramatically lower survivability compared to mice with a 24-hour rhythm.2 If circadian rhythms could vary without bounds, then presumably life would simply adapt to the host planet’s rotation period. However, if bounds exist, then only planets with the proper rotation rate could host complex life. One relevant scenario where this would apply is on planets around M-dwarf stars. Since these stars make up 75 percent of all stars many scientists hold hope that exoplanets around M-dwarfs will host life. However, planets in the habitable zone around these stars don’t rotate. Consequently, it would be impossible to align the circadian rhythms of any hypothetical life with the planet’s clock. Given the unusual set of events that determine Earth’s rotation, such as the collision that formed the Moon, maybe otherwise habitable exoplanets could not host advanced life.
Astronomers still need to learn more before we can truly answer whether life exists beyond Earth’s confines. The advances they have made so far continue to support the idea that only Earth is designed to support life. Such an idea comports well with the biblical description of God who created and fashioned Earth for just that purpose.