How do geologists differentiate between geologic events that took place over thousands of years and those that happened very suddenly or very quickly?

Question

I’m interested in reading about sudden or rapid geologic events, like earthquakes, volcanic activity, and so forth, but haven’t heard a satisfying explanation of this, i.e. whatever I read didn’t stick with me. If someone can give me a basic enough explanation, that would help as I look for stuff like this.

Thanks!

In: Earth Science

Answer 1

There are two ways, both cannot be used together:
1. The Law of Superposition – This basically states that if two layers are superposed on top of each other, then the layer on top happened last.
2. Radiometric Dating – This is used on rocks and fossils. It measures the amount of radioactive decay over a period of time which is then used to calculate the time elapsed since the rock or fossil was formed.