Answer:

The magma that originates from the mantle is in a semi-solid or pasty state due to its high temperature and pressure. As the magma rises to the surface and reaches the earth's crust, it begins to cool and solidify. The cooling process occurs as the magma loses heat to the surrounding environment, which results in a reduction in temperature and an increase in viscosity. The solidification process eventually leads to the formation of solid rock, which makes up the earth's crust.

It is important to note that the solidification process of the magma is not immediate and can take place over a long period of time. Additionally, the rate of solidification depends on various factors, such as the composition of the magma, the pressure and temperature conditions in the earth's crust, and the presence of any impurities.

In summary, the earth's crust is solid because the pasty magma that rises from the mantle undergoes a cooling and solidification process over time, which results in the formation of solid rock.

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