For example, if the unknown layer is above the layer with all the isotopes, we know it is newer than the age revealed from radioactive dating. Simple - eventually we found that there was a ceiling for how big the ages got.
We stopped finding half-lives that were much older than four and five billion years ago.
Imagine you were making a cake with layers of fruit filling in between.
I know, with that kind of talk it may be hard to focus on science, but I'm going to ask you to focus anyway.
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Chances are unless you are a magician and can make things float in mid-air, you'd start at the bottom.By the time you finished the cake, the deeper you went into the cake from the top, the longer it has been since that part of the cake has been on the surface.In fact, if you were to assemble a layer of cake a day, the lowermost layers would be older.These datings put the age of the Earth anywhere from around 7,000 to trillions of years old.However, in the past few hundred years many people have been more inclined to use the scientific method to date the Earth.