It behaves more or less like a solid, but over long periods of time, geologic periods of time, it can flow.

它的行为或多或少有点像固体，但在很长的时间周期里（地质学意义上的周期），它其实是流动的。

They can reveal what species lived during certain geologic periods, how they lived, and how they interacted with their environment.

它们可以揭示特定地质时期生活的物种、它们的生活方式以及它们如何与环境相互作用。

In his hand he wielded with ease an enormous bough, a staff worthy of this shepherd of the geologic period.

他手中轻松地挥舞着一根巨大的树枝，这根手杖配得上这位地质时期的牧羊人。