The World Around Us

Zircon crystal. Significant quantities of helium were found suggesting a much shorter timescale.

Optical microscope photograph of a zircon crystal. This crystal is about 250 µm long. Zircon occurs commonly in the Earth’s crust. As a result of radioactive decay, helium is released and would normally have dispersed from the crystal over the long period of time attributed to this decay. However, significant quantities remain suggesting a much shorter timescale.

Credit: after C M Denniss