Tracing Earth’s history
Although scientists have a general idea of when major events occurred during Earth’s 4.5-billion-year history, geologists would like to be able to pinpoint the exact dates of those events. Precise dates for the sequence and duration of geological events provide insight into fundamental questions about Earth’s history, such as when and why mass extinctions occurred, how long it takes for mountain ranges to form, and the age of Earth’s oldest fossils and crust.One challenge for geochronologists — scientists who determine the age of rocks and minerals — in their quest to develop a geological timescale is how to standardize procedures to allow for precise, accurate dating using different techniques and laboratories. To determine the age of a rock, they measure the abundance of radioactive elements and the elements they turn into over time inside the minerals that make up rocks — the number of atoms of those elements provides an...