Final answer:
Dating the formation of planets can also be done by examining the decay of radioactive elements in rocks, using the half-life concept to calculate when the surface solidified, which has shown Earth and Moon to be roughly 4.5 billion years old.
Step-by-step explanation:
Another way of dating the formation of planets, apart from counting craters, involves examining radioactive rocks. The dating technique is based on the principle of radioactive decay. The age of rocks can be calculated by measuring the proportions of radioactive elements and their decay products. This method relies on the property known as the half-life, which is the time required for half of the radioactive atoms in a sample to decay into stable forms. By knowing the half-life and measuring the ratio of parent isotope to daughter isotope, scientists can estimate the time since the rock layer solidified, providing an age for the surface. This process has helped determine that the Earth and Moon are around 4.5 billion years old.