How tiny Zircon Crystals – Zirconium silicate (ZrSiO4) helped determine the age of the Earth (at approximately 4.5 Billion years old since the crust cooled), with Radiometric U-Pb (Uranium-Lead) dating.
Zircon Crystals trap Uranium Atoms in its crystal structure and naturally repel Lead Atoms when the crystal forms. Once the crystal structure is formed, nothing is able to escape. Over time the isotopes of Uranium start to transmutate into other elements in a process that is referred to as a decay chain.
An Uranium Atom first transmutates into a Thorium Atom (which takes a few billion years). Thorium is far more unstable, and in less than a month it turns into Protactinium. Within a minute Protactinium Atoms transmute again, and so the transmutation continues down the decay chain. At the end of the radioactive decay chain, the initial trapped Uranium Atoms finally decays into stable Lead (Pb) Atoms, which will remain Lead forever. The decay rate and time associated with each transmutation is constant in the Universe, which makes it possible to calculate the age of the crystal with Radiometric dating.
As Zircon Crystals are tough, it is the oldest geological time-capsules that survived in Earth’s dynamic and ever-changing crust since it cooled. As nothing can get in or out of the Zircon Crystal structure, it is the most accurate way of geological dating.
By comparing the Uranium to Lead ratio in Zirconium silicate crystals on Earth, from Moon samples and from visiting Meteorites, Scientists were able to calculate that the Earth is 4.54 billion years old. The error margin is 50 million years, which is small considering the time-scale.