 We've just come up with a relative timescale of events that happened in the rocks down at State Circle. Now if I were to go to another area of Canberra, and for example if I were to see some limestone with some volcanic rocks on top of them, and then if I were to look under the limestone and I could see the same sandstone unit that we saw down there, I could join those two stories together that that would be a story involving rocks deposited in a deep marine environment, then uplifted after land eroded away with the sea coming back in depositing sandstone, then limestone, and then all of a sudden we had volcanoes coming through depositing ash in this area. I could do that actually across the entire earth. I could look at rocks from time spanning from the beginning of the earth all the way up to the present day, and I could make a massive relative timescale of events. And actually the geological timescale that you've probably seen was made in exactly that way. People from all around the world looked at rocks from all around the world of so many different ages, and they came up with this sequence of events. And actually these rocks, the names here come from names of actual rocks that people studied. So for example the Cretaceous is named after some calcium carbonate rich rocks found in the upper Cretaceous that some people studied. The Jurassic Period is named after the Dura Alps. So actually all of this was actually done before we could date anything, absolute dating methods. So we kind of had this relative timescale, and then in the early 1900s finally when we were able to radiometrically date things, we were able to add absolute dates to this timescale that we had created.