Sending probes to look for life on Europa and Enceladus? Good idea. Using the James Webb Space Telescope to search exoplanets for biosignatures? Great idea. Using SETI to find extraterrestrial radio signals? Even better idea. But these are all long-term projects that pose significant logistical challenges, tangible progress could be many years away, and success—i.e., actual discovery of new life—is uncertain.
But the good news is that we’ll probably discover completely new, alien ecosystems right here on our provably habitable, and only partially explored, home planet. We can still boldly go where no one has gone before by investigating…
1. Earth’s mysterious underground superocean.
We’ve only explored about 0.4% of the Earth’s total mass. It might turn out to be the most interesting 0.4%, but the fact remains that almost everything we might ever find on Earth is underneath us. For all of human history, Earth’s explorers have been—quite literally—just scratching the surface.
And this may actually turn out to mean that we’ve never been anywhere near Earth’s largest ecosystems. Geologists are increasingly certain that a massive ocean (or “hydrous mantle transition zone”), larger than all of Earth’s surface water combined, lies underneath us. It’s not at all unrealistic that this superocean might contain life; even intelligent life isn’t completely beyond the realm of possibility. We’re talking about what may be a completely unexplored underground ecosystem, larger than the oceans of Europa and Enceladus combined, on a planet that we already know to be habitable. What’s not to love?
The trouble is that in some respects it’s actually much easier to travel through 390 million miles of space than it is to travel through six miles of solid rock. Over the next ten years, the Japanese Chikyü vessel will allow humans to directly access Earth’s upper mantle for the first time—by digging through the ocean floor to get to it—and that may give us evidence of life under the crust. Or it may not. Either way, this will only be the first step in the very long process of exploring the 99.6% of Earth that is as alien to us as the surface of any new world.
2. The upper atmosphere.
In September 2013, British molecular biologist Milton Wainwright flew a high-altitude balloon over England and found something he didn’t expect to see: algae floating 17 miles above Earth’s surface. We’re not sure how it got there, and until we have a solid theory we have no reason to assume that these algae are the only life forms we’ll find in the skies of Earth.
3. The ocean floor.
It’s a commonly-cited (and accurate) statistic that less than 5% of the ocean’s floor has been explored. There are two ways to read this figure: one is to look at the ocean as if it’s an aquarium, and to say that we’ve neglected the floor because everything interesting is swimming around inside it above the surface. But the other is to look at the ocean floor as if it were land, which it is, and realize that we still haven’t mapped over 95% of it. If we’d only mapped 5% of a continent, how well-explored would we say it is?
Dry land only makes up 29% of Earth’s terrain; the rest of the surface is hidden from us by massive amounts of water. We don’t know what we’ll find at the deepest depths, though what we’ve already seen suggests that a lot of it is going to be really freaking weird.
4. The frozen world.
Global climate change has thawed out fresh mammoths, living megaviruses, and the mummified bodies of World War I soldiers. As this process continues, we’ll no doubt discover new forms of life—and very old forms of life—buried, and preserved, underneath the ice. (That’s assuming the same warming process doesn’t kill us first, of course.) Studying these ancient, well-preserved remains before they decay is going to pose a challenge for scientists.
5. Our own bodies.
In a very real sense, each of us is a walking planet full of diverse microbial ecosystems of unimaginable complexity. And there are more than seven billion of us.
We’ve long known that we’re full of bacteria (collectively, the amount of bacteria in your body weighs about as much as your head), and the Human Microbiome Project has made strides towards cataloguing them. But now, scientists have uncovered evidence suggesting that there’s an undiscovered microbial ecosystem that includes bacteria-eating viruses that feed on our bacterial flora, and there’s no reason to believe that this is the last microbial surprise our bodies hold.
While we’re working to discover evidence of past microbes on Mars, we’re still discovering new things about the microbes that live in our pores and between our teeth. While we’re looking to explore the oceans of Enceladus and Europa, we’ve only just begun to explore the oceans of Earth’s crust—and we haven’t even touched the ocean of Earth’s mantle. And while we explore the skies of exoplanets for atmospheric biosignatures, our own atmosphere contains life that remains, on the whole, mysterious to us. It’s an exciting time to be an astronomer, without question—but it’s also an exciting time to study the largely alien planet that produced us, and to meet the creatures who share it with us. For all of our advances in mapping this planet and cataloguing what we find on it, there’s still a great deal of exploring left to do.