Final answer:
The absolute age of the zircon crystal was determined using Uranium-lead dating, which calculates the age based on the decay ratio of uranium to lead isotopes over time.
Step-by-step explanation:
Scientists determined the absolute age of the zircon crystal in the photo, number 12, using b) Uranium-lead dating. This method is a form of radiometric dating, which is used to determine the exact age of rocks and minerals. For zircon crystals, geologists analyze the chemistry and calculate the ratio of uranium to lead isotopes within the crystal to determine its age. Given that uranium decays to lead at a known and stable rate, the ratio of parent (uranium) to daughter (lead) isotopes can reveal the number of half-lives that have passed since the crystal formed. Since uranium has a half-life of 4.5×10⁹ years, this method is particularly effective for dating ancient materials, and it can yield ages between approximately 4,500 to 5 million years (Ma).