As bored children buckled in backseats, we grow familiar with the way raindrops on glass slide together and coalesce. At pasta-cooking age, we learn that oil droplets in water also glom together, forming bigger droplets until they all become a single globule in the middle of the pot. Intuition tells us that droplets like to combine, even if we don’t know why. (They do it to minimize surface area, since their constituent molecules prefer one another’s chemical company to the surrounding fluid’s.)
Recently, researchers discovered that these familiar droplet dynamics are only part of the story. As I describe in a Quanta article this week, droplets that are “chemically active,” using sunlight or some other energy source to constantly cycle molecules into and out of the surrounding fluid, behave in unexpected ways that might have played a critical role in the genesis of life on Earth.
Unlike the familiar droplets of our youth, active droplets grow to roughly the size of a cell and stop growing; they also spontaneously divide, producing daughter droplets. The findings, by a team of biologists and physicists in Dresden, Germany, have revived a hypothesis, first suggested in 1924, that liquid droplets in early Earth’s primordial soup were the primitive precursors of the first cells. As these active-droplet “protocells” divided and proliferated, evolution could have acted on them, gradually making them more complex and leading to the rise of living cells.
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