To fossilize means to turn into a fossil, which is the preserved remains or traces of an ancient plant or animal. When a dinosaur died millions of years ago and its bones gradually turned to stone over countless centuries, those bones fossilized. The process happens when minerals in water slowly replace the original material, creating a rock-like copy of what once lived.

Scientists study fossilized bones, shells, and even footprints to learn about creatures that lived long before humans existed. A fossilized fern leaf pressed into rock can show us what plants looked like 300 million years ago. Fossilized dinosaur eggs reveal how these massive reptiles cared for their young.

The word also describes ideas or ways of thinking that have become rigid and outdated. When someone's opinions have fossilized, they've stopped adapting to new information, like ancient bones that can no longer change. A teacher might warn that studying the same way for every subject can lead to fossilized thinking, when flexibility would serve you better. Unlike actual fossils, which teach us about the past, fossilized ideas can hold us back.