Relative dating diagram
which friends we knew at which stage of our lives).But unless we have been revising a CV or resum recently we may be less clear about the precise years in which particular things happened (that is, absolute chronology).
So far, so good – but we still don’t have a way of pinning our relative sequence down in time.Here the assemblages are represented by different symbols (star, square etc.), arranged in chronological order with the oldest at the bottom.Relative dating, shown in Diagram 2, is like playing the slot machines: you want at least two identical things to line up at the same time. Here, the process of lining up contemporary assemblages reveals that the three sites have some chronological overlaps.The lava flow took place some time after the diorite cooled, was uplifted, and then eroded.(Hammerhead for scale) [SE]Figure 8.6b Rip-up clasts of shale embedded in Gabriola Formation sandstone, Gabriola Island, B. The pieces of shale were eroded as the sandstone was deposited, so the shale is older than the sandstone.
are surfaces in rocks caused by erosion or non-deposition that represent missing time. This Fairfax County unconformity represents about 500 million years that are not represented between the top of the granite and the bottom of the Coastal Plain sand deposit.