If you look at the Moon, even without a telescope, you see broad areas where its surface appears relatively darker and smoother. These areas are individually called mare (plural: maria), from the Latin word for sea. The term is misleading, for they are not bodies of water but rather plains of igneous rock formed after huge meteors struck the Moon and formed very deep craters. These impacts occurred early in the history of the Moon. Propose a cause for the igneous activity, and suggest the type of igneous rock that fills the mare. (Hint: Think about how the presence of a deep crater affects pressure in the region below the crater, and think about the viscosity of a magma that could spread over such a broad area.)

Step by step solution

01

Determine the cause of igneous activity in maria

When a huge meteor strikes the Moon, it creates a very deep crater. The impact of the meteor causes a sudden and significant increase in pressure in the region below the crater. This increased pressure generates enough heat to partially melt the lunar mantle, producing magma.

02

Consider the viscosity of the magma

In order for the magma to spread over a large area like the maria, it must have low viscosity. Low viscosity magma is typically less resistant to flow and can spread easily over the surface. This allows for the formation of the broad, relatively flat areas we observe in the maria.

03

Suggest the type of igneous rock that fills the mare

Considering the low viscosity magma that spreads easily over the lunar surface, the most likely type of igneous rock that fills the maria is basalt. Basaltic lava flows are generally more fluid and can cover large areas, forming the broad plains observed in the maria. This type of rock is also darker in color, which corresponds to the dark appearance of the maria compared to the rest of the Moon's surface. In conclusion, the cause for the igneous activity in the Moon's maria is the increased pressure generated by meteor impacts, which produces magma. The magma likely has low viscosity, allowing it to spread over large areas, and the type of igneous rock that fills the mare is basalt.

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