How long ago did diamond form

Question

IF it is billions of years ago then how come we find carbon 14 in diamonds

Answer 1

they were discovered 2.5 billion years ago.

but they were  actually formed long long long long before that.

it takes about 200 years to form so since the earth first existed.

my wording didnt get mixed up.

there were people 2.5 billion years ago

Answer 2

Diamonds form relatively quickly... but they tend to form very deep within the earth's mantle, so it can take billions of years for them to rise to a depth that humans can find them.

However, they CAN also form near the surface, for example, at the site of a meteorite impact, which is capable of generating the intense heat and pressure required for diamond formation.  These diamonds, being very near the surface when they form, tend to be much younger when humans stumble across them, which means that their C-14 levels are still detectable.