Maria & Terrae

- Distinguish between the lunar seas (maria) and highlands (terrae)
- Demonstrate an understanding of the origin of lunar seas and craters
- Demonstrate an understanding that the relative numbers of craters in the seas and highlands implies different ages of these features

Mare (pronounced Mah-ree) is the Latin for sea. Maria is the plural, seas (porinounced Mah-ree-a).

These are dark areas on the Moon. Approximately 17% of the lunar surface is classed as maria. These were mistaken by early astronomers for seas.

Terrae is the collective name for highlands – bright areas that are higher on the Moon’s surface than maria.

Maria appear darker than the terrae as they contain more iron-rich elements. There are few maria on the far side of the moon.

Rocks brought back from the Apollo missions have shown they were formed 3-4 billion years ago.

There was a period called the ‘Heavy Bombardment’ when the Moon (and presumably the inner Solar System) underwent a time of frequent and violent impacts.

Millions of years (sometimes as many as 500 million years) later the Moon underwent a time of volcanic activity and lava was forced to the surface. This lava later turned to basalt. It flooded the lower impact areas and would have covered any other features on the landscape including other craters. The highlands were left untouched.

Today we can see a large number of craters on the Terrae and fewer on Maria which also implies they were formed at different times.



  • Why do scientists think that maria formed later than the highlands?
  • Explain how maria may have been formed.

Terra – brighter, more cratered

Maria – darker, less cratered


Backyard Astro Copernicus and Montes Riphaeus