Gordon's answer is correct to a first order approximation.
However, the zircons that were found in Jack Hills are from the Hadean, more than 4 billion years ago. The fact that zircons that old exist is interesting - zircon is not a mineral you find in mafic rocks. Zirconium is an incompatible element in the mantle, so to get enough of it to form its own mineral you need some partial melting events. This may also be of interest:
What are the high field strength and large ion lithophile (HFS or HFSE & LIL or LILE) elements?
When you melt the mantle, you end up having basalt or more felsic rocks. If you have enough zircon in mafic rocks, you form baddeleyite: ZrO2. Zircon, ZrSiO4 will only form in more felsic rocks, where you have enough Si. This alone suggests that some parts of the early crust was somewhat more felsic than a basalt.
There's more to it: inclusions of quartz and oxygen isotope data indicate that not only the zircon was in a felsic rock, it has evidence to suggest liquid water and hydrothermal alteration.
This entire thing is heavily debated, because there's only so much you can tell from a few grains of zircon. However, the basics are there - some felsic rocks existed as far as the Hadean.