There are many kinds of evidence that teach us about the past: majestic
pyramids, the ruins of an ancient city, pieces of pottery, even a simple trash pit.
Every piece of evidence has one thing in common—it's lasted a long time.
Most things from the past, like fabric, wood, and food, decay over
time. Things made of clay, metal, and stone survive much longer. What survives also depends on the environment. In a rain forest, a wooden
spear would rot and decay. But in a desert, the same spear might be preserved by the dry air.