Billions of years ago, the Moon was volcanically active. Lava erupted through cracks and filled massive basins. These flows created the dark lunar maria. The eruptions lasted hundreds of millions of years. Unlike Earth, no plate tectonics recycled the crust. The lava simply cooled and stayed.
This matters because maria shape what we see from Earth. They affect reflectivity and thermal behavior. The Moon’s face is volcanic history.
It also shows that small worlds can be active early on. Size doesn’t prevent geological drama. Timing matters more.
Some lunar lava flows were over 100 meters thick. They covered areas larger than some countries.
NASA [nasa.gov]