Fossil coral dating pros and cons to online dating
Horn coral, any coral of the order Rugosa, which first appeared in the geologic record during the Ordovician Period, which began 488 million years ago; the Rugosa persisted through the Permian Period, which ended 251 million years ago.
Horn corals, which are named for the hornlike shape of the individual structures built by the coral animal, were either solitary or colonial forms.
Of the many forms known, some are important as index, or guide, fossils for specific spans of geologic time and serve to correlate sometimes widely separated rock units.
Because of their mode of growth, some horn corals have been employed as biological clocks to determine the length of the day and year in the distant geologic past.
, which is about the birth of stratigraphy as a field of study and how we came to know that our Earth is billions of years old.
To summarize, though: generally speaking, if you cut a slice down through a section of rock (like for a highway through the mountains), you see a stack of layers of different kinds and colors of rock.
The key insight here is that usually the rocks closer to the surface are NEWER than the deep-down layers, because rocks are formed by gradual deposition from up here where we walk around and drop stuff.
So if you draw a diagram of what the layer-cake looks like near where you live, and then go fifty miles away and draw what THAT layer-cake looks like, and so on, you've collected a bunch of specific samples of the history of the rocks in your area, like looking at tree rings.
Distinctive fossils are one way we can match up fossil layer-cake diagrams from one area to another, because if a fossil only ever lived at one time, then you can line up the diagrams and see which other layers are consistently older, or consistently younger, than that distinctive layer.So far, so good, but that only gives RELATIVE dating (which thing is always older than what other thing -- like an alphabetic order, although not all areas have all layers of rock in them). Because we have such good, large datasets about differing relative dating, you can get pretty close on other layers if you can absolute-date just one or two layers in the cake. Let's say you have a single atom of a radioactive isotope, say carbon-14.I'm going to skip the very technical parts to save some space, but what makes it "radioactive" is that it tends to decay to the much more commonplace isotope carbon-12.It is in the nature of radioactive decay that we can't put on a calendar, "My pet atom Addie is going to decay on June 15th, 2020" and know it to be true; there's a random factor involved.
But, statistically, on large groups of atoms, we know that about half of them will have decayed in a specified interval: the half-life of that substance.
We call it the "half-life" because, statistically, you can rely on estimating that half of a given sample will have decayed (changed weight) in that amount of time.