Often you will be told in science class that fossils take thousands of year to form, but looking at fossil pictures below you will see that they can form very fast!
This fish was swallowing his dinner when he got fossilized, how long do you think he waited?
This orange was found in an orange orchard. The orchard was less than 150 years old. Notice that this orange had not begun rotting before it was fossilized.
So what do you need to make a fossil?
If the ground is very mineral rich and wet, wood can fossilize in just a few years. If it is hot too (like the side of a volcano after an eruption) it can fossilize in a few days or weeks! This happened When Mt. Sain Helens, Washington state, erupted in 1980. There are petrified (fossilized) trees there already.