Okay

We know that K-40, potassium 40, decays into two atoms

since it’s radioactive

Argon 40, and Calcium 39

We know that 11% is argon 40, and 89% is Ca 39

Isn't it Ca-40?

@NickC64 sorry I had to go, I'm at work)

No

Lol

One of the neutrons turns into an electron

Pretty sure

Maybe proton

Alright

And if we have some sort of volcanic eruption, the lava is illiquid

Liquid**

That means that any argon 40 in there, since it’s low reactivity, is free to move out of the lava

Perhaps an error in the wikipedia article then, it says Ca-40

It’s probably an error

@PhumoZTYPE anyway

Because of this, we know that any argon 40 in the rock must have came from the parent element

Which is K-40

Yup

Good

Now, we can get to the fun part

It would be easier if I could send pictures

Yeah I guess

We can take our original equation, N_0 times e^-kt = N(t)

Checked, it's Ca-40 from beta decay of K-40

I’ll have to read up on that then

K-40 to Ar-40 is by electron capture

It’s irrelevant to this discussion though

All we care about is Argon 40

I shall keep my mouth shut then

@PhumoZTYPE

Yeah

I’m listening

We can plug in 1.25B to our equation for t

And set it equal to 1/2 N(t)

Why lol

Because in 1.25 billion years, we’ll have half the amount of K-40

Oh yess