The ages of Martian highlands, basins, and Tharsis volcanoes can be determined by counting the number of impact craters on their surfaces¹. The more craters there are, the older the surface is. This method is called "crater counting" and it is based on the assumption that all surfaces were bombarded by meteoroids at a constant rate over time¹. However, this method has limitations as it assumes that the rate of impacts has been constant over time, which may not be true¹. Therefore, other methods such as radiometric dating are used to cross-check the ages derived from crater counting¹.
Radiometric dating involves measuring the abundance of isotopes in rocks and minerals². The age of a rock can be determined by comparing the abundance of isotopes of a radioactive element to its decay product². For example, potassium-40 decays into argon-40 with a half-life of 1.3 billion years². By measuring the ratio of potassium-40 to argon-40 in a rock, geologists can determine its age².
The ages derived from these methods are not certain as they depend on several assumptions and uncertainties¹. However, they provide a rough estimate of the age of Martian features.