When was potassium argon dating first used latest lesbian dating
But what's neat about argon-40 is that while it's lava, while it's in this liquid state-- so let's imagine this lava right over here. And so what you can do is you can look at the ratio of the number of potassium-40's there are today to the number that there must have been, based on this evidence right over here, to actually date it.
And in the next video I'll actually go through the mathematical calculation to show you that you can actually date it.
The attraction of the method lies in the fact that one of the daughter elements is argon which is an inert gas.
This means that the geologist can plausibly assume that all argon gas escapes from the molten magma while it is still liquid.
And the reason this is really useful is, you can look at those ratios.
And volcanic eruptions aren't happening every day, but if you start looking over millions and millions of years, on that time scale, they're actually happening reasonably frequent. So let's say this is the ground right over here.
It's not bonded to anything, and so it'll just bubble out and just go out into the atmosphere. That lava will contain some amount of potassium-40. And so you know the only way this argon-40 can exist there is by decay from that potassium-40. So you know for every one of these argon-40's, because only 11% of the decay products are argon-40's, for every one of those you must have on the order of about nine calcium-40's that also decayed.
So what's interesting about this whole situation is you can imagine what happens during a volcanic eruption. And actually, it'll already contain some amount of argon-40. And let me do it in a color that I haven't used yet. And so for every one of these argon-40's you know that there must have been 10 original potassium-40's.
And this is actually the most common isotope of potassium. This accounts for about 6.7% of the potassium on the planet. And as we'll see, when you can date old volcanic rock it allows you to date other types of rock or other types of fossils that might be sandwiched in between old volcanic rock.On the other hand, if the rock was later disturbed by a geological upheaval and lost argon the age would be too young. In other words, he checks to see if his calculated result falls into the range where he expects it to fall, given the geological situation of where he found his rock.He always does this check because no dating method can be trusted on its own. It’s simple; the geologist will change his assumed history for that rock.And he hopes the rock has remained sealed until the time he collected his sample.the geologist only needs to measure the relative amounts of potassium-40 and argon-40 in the rock at the present time to be able to calculate an age for the rock.
Because what's cool about argon, and we study this a little bit in the chemistry playlist, it is a noble gas, it is unreactive. And you know that it has decayed since that volcanic event, because if it was there before it would have seeped out.