When living things die they are sometimes buried in a layer of mud. After millions of years the mud turns into solid rock and the remains are preserved as fossils . The layers of rock can be dated, and so we know the age of the fossils in that layer. Paleontologists have discovered much about life that existed millions of years ago, by studying fossils. Especially interesting are the fossils of dinosaurs, some of which were very large indeed.
Paleontologists know what they looked like and what they ate.
Physics is the science of matter and energy, including light, sound, electricity, magnetism, radiation, and motion . Nuclear physics studies atomic particles and the energy they contain - which has led to the development of nuclear energy and weapons in the first half of the twentieth century. Physicists work with a mixture of theory and experiment. They perform experiments and try to construct theories to explain their results. These theories should make predictions which can be tested by new experiments.