These include radiometric dating of volcanic layers above or below the fossils or by comparisons to similar rocks and fossils of known ages.
Knowing when a dinosaur or other animal lived is important because it helps us place them on the evolutionary family tree.
Despite seeming like a relatively stable place, the Earth's surface has changed dramatically over the past 4.6 billion years.
Mountains have been built and eroded, continents and oceans have moved great distances, and the Earth has fluctuated from being extremely cold and almost completely covered with ice to being very warm and ice-free.
A common problem with any dating method is that a sample may be contaminated with older or younger material and give a false age.
This problem is now reduced by the careful collection of samples, rigorous crosschecking and the use of newer techniques that can date minute samples.
Although most attention in today's world focuses on dinosaurs and why they became extinct, the world of paleontology includes many other interesting organisms which tell us about Earth's past history.
The study of fossils and the exploration of what they tell scientists about past climates and environments on Earth can be an interesting study for students of all ages.
Sequencing the rock layers will show students how paleontologists use fossils to give relative dates to rock strata.However, "relative" dating or time can be an easy concept for students to learn.In this activity, students begin a sequencing activity with familiar items letters written on cards.For example, based on the primate fossil record, scientists know that living primates evolved from fossil primates and that this evolutionary history took tens of millions of years.By comparing fossils of different primate species, scientists can examine how features changed and how primates evolved through time.