What did researchers determine about the zircon in the sandstone samples that they studied? A. Zircon tends to decrease the rate at which sandstone weathers. B. Zircon was unusually abundant in sandstones from the Gondwana supercontinent. C. Zircon in sandstone from Australia is as old as the Himalayas. D. Zircon of the same age is found in sandstone samples from different continens.