Final answer:
Dinosaur fossils are found in the Triassic, Jurassic, and Cretaceous periods, which constitute the Mesozoic Era, known as the Age of Dinosaurs. These periods saw the emergence, diversification, and eventual extinction of dinosaurs.
Step-by-step explanation:
The three geologic periods where dinosaur fossils are found are the Triassic, Jurassic, and Cretaceous periods. These periods collectively make up the Mesozoic Era, often referred to as the 'Age of Dinosaurs'.
The Triassic Period spanned from about 251.9 million years ago to 201.3 million years ago and saw the emergence of the first dinosaurs. The Jurassic Period, from about 201.3 million years ago to 145 million years ago, was known as the golden age of dinosaurs and brought forth significant dinosaur diversification. The final period, the Cretaceous, lasted from about 145 million years ago to 66 million years ago and ended with a mass extinction event that wiped out the dinosaurs.
Fossils of dinosaurs found from these three periods provide crucial insights into the evolution and diversity of these ancient creatures, as well as the environments they inhabited.