Before there was life, there was not life. There were rocks and sea and dirt; then there were creatures. There were sugars and amino acids and bubbles and water and oil, and then there was an organized system: life.
Until the 19th century, the idea of life arising from inanimate matter was taken as the status quo. Some living things required parents — humans, dogs, other animals we’d seen giving birth, and plants we’d seen sprouting from seeds — but sometimes, it was thought, spontaneous generation was the rule. When meat sat out too long, maggots started to grow out of it; ergo, maggots spontaneously generated from the meat. A rotting log sprouted mushrooms. Or maybe animals arose from other animals, but not their own kind — a tapeworm birthed by the creature we now understand to be its host.
We learn this story in biology classrooms as proof of how naive and backward humanity once was. But as whimsical as the idea of mice arising from hay may seem now, spontaneous generation must have happened on Earth at least once. There wasn’t life, and then there was. The origin. Abiogenesis — literally, life from not-life.
In those same biology classrooms, we learned a story that has stuck around since the 1950s, that of the “hot, weak soup,” a prebiotic murk shocked by lightning strikes into something more. High schoolers still learn a version of this today, but the science is much weirder and stretches all the way into space.
“How did life begin on Earth?” is a question where science and imagination are one and the same. It’s an utterly unanswerable question, at least barring a time machine and extreme precision. A visit to just the right moment at the right murky shallows, when some twisty molecules in a tiny bubble membrane of clay or oil crossed an undefinable line. Did life begin with metabolism — the ability to thwart entropy and draw energy from the environment? Or was it about coding information, molecules that drive their own replication? Even if you made life in a lab, you could never know how life was actually first made here.
Scientists in this field work with these broad questions and many narrower ones: How might particles of clay knit into a vesicle to give some prebiotic molecules a home? Were those building blocks of life cooked up in our seas, or in the high atmosphere, or out in the depths of interstellar space?
And when we look to other planets, will the story there be the same? When scientists talk about signs of life, they mean signs of life as we know it: They look for water, oxygen, the spectral signature of photosynthesis. But is that a failure of imagination? Is it anthropocentrism or the simple facts of chemistry, of atomic orbits and molecular stability? How different from ours can the building blocks of other life be?
The story of the origin of life on Earth will likely always be a mystery, always a pile of questions. Scientists can work toward understanding how it might have happened, but there’s no way to make an observation to confirm your hypothesis, no way to know how life started here. Forget the n=1 problem of trying to extrapolate from Earth to other planets. This is n=0: trying to understand the prevalence of life in the cosmos without ever being able to know for sure how it started here.
When we look to the cosmos, instead of back through time, there is an answer out there. One way or another. And so we can’t set aside our curiosity, saying, We’ll never know, but it’s a fascinating puzzle! Either there’s life beyond Earth or there isn’t; either intelligent aliens are out there or they’re not. It seems so much simpler, a binary fact, but the mystery of it taunts me, because it’s not just a question—it’s an answer out of reach.