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Radioactive dating of moon rocks

Look closely at the Geologic Time Scale chart, and you might notice that the first three columns don't even go back 600 million years.

Simple enough, see the meteorites formed alongside the planet, however, since the planet was pretty much a molten soup you can't date it properly, because we can only date it after it cooled down.

Meaning that the meteorites hold a much more accurate time-frame since they were not melted down to form our crust!

Some background: We are able to determine the age of certain rocks and minerals using measurements of radioactive and radiogenic isotopes of certain elements. Simply put, the resulting date is the time that has passed from the crystallisation of that mineral.

Obviously there are complexities, but there are not critical for this answer.

When you find the same fossils in rocks far away, you know that the sediments those rocks must have been laid down at the same time.

The more fossils you find at a location, the more you can fine-tune the relative age of this layer versus that layer.

On Earth, we have a very powerful method of relative age dating: fossil assemblages.

Paleontologists have examined layered sequences of fossil-bearing rocks all over the world, and noted where in those sequences certain fossils appear and disappear.

When you talk about something happening in the Precambrian or the Cenozoic or the Silurian or Eocene, you are talking about something that happened when a certain kind of fossil life was present.

Major boundaries in Earth's time scale happen when there were major extinction events that wiped certain kinds of fossils out of the fossil record.

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