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
For volcanic events we have several ways to date the volcanic deposits. There are for example certain radioactive elements that are embedded in minerals. Over time those elements decay radioactively into other isotopes or whole new elements. By comparing the ratios between the original element and the new ones we can determine an approximate age of the deposits. There are a lot of different dating methods, which all work best for a specific timeframe.
Often we can also use fossils to determine age. If for example the eruption killed specific animals and we know when they were around we can get an approximate age. Even spores and pollen can be embedded in these layers and we can use those for dating.
As for earthquakes We can’t actually know when past ones happend if they weren’t recorded by humans.
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.
In most geologic time, 1,000 years is almost instantaneous.
There is a thing called the KT boundary the boundary between the Cretaceous and Tertiary periods (~~Kreide-Trias~~ Kreide-Tertiär which has now had a namechange to the more precise Kreide-Paläogen in German and it’s now the KP boundary) where in the Geologic record there is a thin layer of clay in the boundary between these periods. This layer of clay is high in Iridium all over the world and strongest in Mexico. Iridium is an element that is rare on earth, but prevalent in meterorites. The conclusion then is that one day a massive meteorite landed on earth and the explosiong sent parts of the meteorite all over the earth (probably similar to how an atom bomb exploded in the air puts trace levels of radioactive contaminants all over the earth.
If we accept the explanation of the meteorite spreading iridium all over the earth and the change from reptile to mammalian then we can conclude that this point in Geological time is precisely known.
ETA /u/GiantClaw points out that KT is Kreide-Tertiär (which was name changed to Kreide-Paläogen) not Kreide-Trias.
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