We've been talking a lot in this blog about the cores we recover, but they're not the only source of data we use. We also get a lot of information out of the holes those cores leave behind. The holes have the same sediment layers as the cores, and unlike the cores themselves, which can be incomplete or mixed-up, the sediments in the ground can give us a very consistent record, hundreds of metres long. We measure the sediments on the walls of the hole in a process called "downhole logging".
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