Zircon Crystals and the age of Earth
The story of Zircon Crystals and Earth's age in a Nutshell.
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.
The background history of Radiometric dating:
In 1896 Henri Becquerel and Marie Curie discovered that certain isotopes undergo spontaneous radioactive decay, transforming into new isotopes. Atoms of a parent radioactive isotope randomly decay into a daughter isotope. Marie Curie won a Nobel Prize in Physics and Chemistry for her work.
The spin-off from trying to date the Earth by finding the Uranium to Lead ratio in Zircon crystals, was that the Scientist Clair Patterson discovered the unusually high amount of toxic Lead in the environment when he tried to analyse the Zircon in a Mass Spectrometer. This was due to the widespread use of Lead-based fuel, Lead-based paint, etc.
Our bodies require metals like Iron in the blood to transfer Oxygen through the body. The body is fooled and assumes that Lead is a good metal, but Lead not only destroys cells, but also blocks the signals of Neuroreceptors in the Brain.
After a lifetime of persistence and mounting evidence, Clair Patterson eventually won the case against the large Oil Companies that tried to discredit his findings. Since then the widespread use of Lead in everyday products were banned (which is why we now use unleaded fuel to power our vehicles).
More about isotopes and the Radiometric dating process.
Thank you to Sumarie for letting photograph her beautiful Zircon Crystal specimen.