Lid tectonics

Lid tectonics, also known as stagnant lid tectonics or single lid tectonics, is a process that scientists believe happens on several silicate planets and moons in our Solar System. It might have even existed on Earth during its very early days. In lid tectonics, the surface, called the lid, is made of solid silicate minerals and is very stable and doesn’t move much.

This stability is different from what we call plate tectonics, where the Earth’s surface moves around a lot. The stagnant lid sits above a layer called the mantle that moves, but the lid itself stays mostly still. This kind of tectonics has much less horizontal movement than plate tectonics.

Scientists think that early Earth might have had a stagnant lid before it changed to the moving plates we see today. This change probably happened between 3.2 and 2.3 billion years ago during a time called the Archean epoch. Understanding lid tectonics helps us learn about how planets and moons, including our own Earth, change over very long periods of time.

Formation

A lid tectonic regime happens when the cold outer layer of a planet, called the lithosphere, is too stiff to move with the flow of the mantle underneath. This stiff layer, or "lid," is strong enough that it doesn't break easily. This situation depends on how strong the lithosphere is compared to the natural movements in the mantle. If the lithosphere is stronger than these movements, then the planet has stagnant lid tectonics, meaning there is much less movement of the Earth's surface compared to places where pieces of the surface shift around more.

Main article: Yield strength

Factors contributing to lid tectonics

Many features of a planet or moon affect whether lid tectonics happens. Things like the temperature near the center of the planet and whether there is water play big roles.

The solid outer layer, called the lid, does not move with the softer layers underneath. Near where the lid touches the softer material below, melted rock can form and drip down. This means the lid stays still and does not mix the layers below very well.

Other planetary bodies

Stagnant lid tectonics is the most common type of tectonic activity found in our Solar System. Planets like Mercury, the Moon, Venus, and Io are thought to have had this type of tectonics throughout their entire history.

On Mercury and the Moon, heat escapes mainly by conduction through the lid, resulting in low amounts of heat flow. Scientists Solomatov and Moresi introduced the term "stagnant lid" to describe the tectonic style of Venus in 1996. They noted that Venus has heat plumes rising to the surface and colder parts of the lid sinking back down. Mars is also believed to have stagnant lid tectonics, though its activity is much slower compared to Venus.