Many factors are involved in making a planet habitable: the size and composition of the planet, the stability of its orbit, its distance from its star. But scientists are still trying to figure out which factors are important.

An example is plate tectonics. Earth’s surface is divided into large “plates.” They glide along the rocks below the surface. They ram together, slide over each other, and recycle the crust. They allow heat to escape to the surface, and affect the chemistry of the atmosphere. So tectonics has been considered a key ingredient for the development of life.

But some recent studies have cast some doubt on that idea. One study found that the early Earth probably didn’t have tectonics. Instead, its crust was rigid — a “stagnant lid.” Instead, molten rock would have punched through the crust, building big volcanoes. That warmed the surface, allowing the development of the first life more than three and a half billion years ago. But the study also suggested that tectonics might be necessary to sustain life, and allow the development of more complex life.

But another study disputes even that. It says that life could last for billions of years on a stagnant-lid planet.

Some models show that plate tectonics could be rare on other planets. But if tectonics isn’t necessary for life, then the number of possibly habitable worlds goes way up — increasing the chances that we might find a “living” planet.

Script by Damond Benningfield