Maria (Latin for "seas") are vast, dark plains of solidified lava that formed billions of years ago during a period of intense volcanic activity.

Craters are impact features that formed throughout lunar history, from the early heavy bombardment period to the present day.

Here's why craters are younger:

* Formation: Maria formed through volcanic eruptions, while craters formed through impacts. Impacts are a continuous process, occurring throughout the Moon's history.

* Superposition: The principle of superposition states that in a sequence of layered rocks, the oldest layers are at the bottom and the youngest at the top. Craters are often found on top of maria, indicating that they formed after the maria solidified.

* Crater density: The density of craters on a surface is a measure of its age. Maria have a lower crater density than the surrounding highlands, indicating that they have been less exposed to impacts since their formation.

Exceptions:

* Very old craters: Some craters formed early in lunar history might be older than some maria.

* Overlapping craters: If a crater is formed on top of an older crater, the newer crater would appear younger.

In general, however, the vast majority of lunar craters are younger than the maria.