Much of what we know about the history of the Earth is based on physical and chemical evidence from the earth. This evidence can be classified in a number of different ways, for example chronological order, by geological processes that formed them, or by characteristics such as their age.
Clues are provided by numerous sources including rocks and minerals (most notably radioactive isotopes), fossils, and climate change observed over time. In other cases, geologists have made inferences about history based on gravity and magnetic data. These methods provide a framework for understanding our planet's past but they do not necessarily reveal an unbroken record.