This article declares that scientists have found a portion of Earth that is part of the original material.

The evidence comes in the form of lava rocks that, themselves, are a mere 60 million years old. But these rocks contain an early Earth mixture of helium, lead and neodymium isotopes which suggest the mantle rock beneath the crust that yielded them is a virgin pocket of Earth's original material.

That pocket had survived for 4.5 billion years under Baffin Island without being mixed by plate tectonics or erupted onto the surface.

I won't even begin to claim that I know how you determine the age of something to be 4.5 billion years old (finding helium-3 / helium-4 apparently) but I think it's fascinating that we're making inroads to finding out more about the true makeup of our planet.

via Ryan.