Which allowed scientists to determine the earth was atleast 4.3 billion years old?

The correct answer is **the radioactive decay of uranium to lead**. This method, known as uranium-lead dating, is one of the oldest and most reliable radiometric dating techniques used in geology to determine the age of the Earth and other geological samples. Zircon crystals, often found in sedimentary rocks, can contain uranium and are used in this process to estimate the age of the rock formations in which they are found, helping scientists conclude that the Earth is at least 4.3 billion years old.