In between are several layers of dense shale rock.

中间是几层致密的页岩。

But out in the rest of the galaxy the most common planets we've found are big, dense, rocks nicknamed Super-Earths.

但在银河系的其他地方，我们发现最常见的巨大且密度大的行星，昵称为超级地球。

This molten material is less dense than when it was solid, causing it to rise above the denser rocks surrounding it and eventually, out through fissures or vents to the surface.

这种熔融物质的密度低于固体时， 导致它上升到周围更密集的岩石之上，最终通过裂缝或通风口到达地表。