Prefixed SI units of time longer than a second are rarely used because the traditional units for periods longer than a second such as years are still generally used. One petasecond is approximately 31.7 million years, meaning the unit can be used to specify events that occurred millions of years ago or lasting millions of years. The dinosaurs went extinct 2.07 petaseconds ago (66 million years ago). The Permian-Triassic extinction began 7.95 petaseconds ago (252 million years ago). Multi-cellular animals have been around for approximately the last 20 petaseconds (600 million years). The Supercontinent Pangaea broke apart around 6 Ps ago (175–200 million years ago). The Earth is about 143 Ps old (4.54 billion years old). The Sun takes 7.13 Ps (226 million years) to orbit around the center of our Milky Way Galaxy.