Radiometric dating of sedimentary rocks online dating is hell

I asked in the caption to this figure, “How do you know C happened before D? If you’re familiar with the colors and patterns used in geologic diagrams like this, you probably know that D is an igneous intrusion and C is a layer of sedimentary rock.

So we know that C came before D—but because D is igneous, we can put a date on it (now I have a Beyoncé song in my head, great…).

radiometric dating of sedimentary rocks-81

-Correlation by fossils- same fossil or fossil assemblage in widely separated rocks are same age. age of rock = number of half lives gone by X half life of isotope pair used How old is the Earth?

The shorter the range of the fossil, the more accurate the correlation. -oldest rocks dated are from Greenland, Minnesota, etc.

As the rock cools, there comes a point, called the closing temperature, when parent and daughter isotopes can no longer diffuse into or out of the rock system—at that point, the clock is set.

(It’s worth mentioning that this temperature varies by rock type and by isotope!

It’s just that I kept adding and adding to make it all make more sense and before I knew it, I had 3000 words on dating fossils! So, last time, we discussed the basics of radiometric dating and ended with a quick and dirty example of how a parent:daughter isotope ratio can be used to find the age of a sample.

I skipped some details on purpose, but the foundational principles to these methods are really as easy as I explained.

So it’s not like there is one magic temperature that locks these things in. Carbon-14 is a radioactive form of carbon that is widely used in radiometric dating.

It’s all a bit mathy, but the good thing is, people have figured it out and can account for it no matter the rock type or the radiometric method being used.) But, when it comes to fossils, we’re primarily interested in sedimentary rock layers, which, you’ll recall, form from pre-existing rock material. Very occasionally, there may be some remaining organic material in a fossil that could, hypothetically, be dated using carbon-14.

And when you consider that sedimentary rocks are where fossils are found, you might despair of the prospect of using radiometric dating to ascertain the age of your favorite fossil. Carbon-14 is basically useless if what you’re interested in is more than 50,000 years old—which, for pretty much all paleontologists, includes just about everything. Radioactive dating also helps to date metamorphic rocks, but since metamorphosis happens to preexisting rocks, those dates aren’t very useful to know because they don’t help you to put anything in order.

Tags: , ,