Difference between relative and chronometric absolute dating techniques


That's why geologic time is usually diagramed in tall columnar diagrams like this.Just like a stack of sedimentary rocks, time is recorded in horizontal layers, with the oldest layer on the bottom, superposed by ever-younger layers, until you get to the most recent stuff on the tippy top.If you know when the top or bottom layers were formed - you know just about when was the middle one formed.Geologists use radiocarbon to date such materials as wood and pollen trapped in sediment, which indicates the date of the sediment itself.

The Geologic Time Scale is up there with the Periodic Table of Elements as one of those iconic, almost talismanic scientific charts.There's no absolute age-dating method that works from orbit, and although scientists are working on age-dating instruments small enough to fly on a lander (I'm looking at you, Barbara Cohen), nothing has launched yet. Relative age dating has given us the names we use for the major and minor geologic time periods we use to split up the history of Earth and all the other planets.When you talk about the Precambrian, Paleozoic, Mesozoic, and Cenozoic on Earth, or the Noachian, Hesperian, and Amazonian for Mars, these are all relative ages.However, archeologists still require further information to find out the items that are oldest and those that are youngest in the order.Similarly for paleontologists who find layers of fossils.Long before I understood what any of it meant, I'd daydream in science class, staring at this chart, sounding out the names, wondering what those black-and-white bars meant, wondering what the colors meant, wondering why the divisions were so uneven, knowing it represented some kind of deep, meaningful, systematic organization of scientific knowledge, and hoping I'd have it all figured out one day.

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