A rainforest trapped in Amber.

A group of paleontologists has found gold in the western Amazon. No, not the type of gold that's made into jewelry or coins. Instead, the fossil-hunting scientists discovered ancient, gold-colored rocks that have tiny plants and insects trapped inside.

These fossilized plants and animals are valuable because they provide the best evidence yet that rainforests existed in the western part of the Amazon basin as long as 15 million years ago.

The researchers estimate that the little flies, gnats, and other bugs found in the amber became trapped 10 to 15 million years ago. At that time, sticky resin from trees covered the insects, along with plant pollen, fungi, and other tiny organisms. The resin hardened into amber and became lodged in layers of rock. The scientists found 28 of these gold-colored nuggets during their search near the Amazon River in northeastern Peru.

After they dug up the rocks, the paleontologists used microscopes to study the trapped fossils. In this way, they didn't have to crack open the rocks and risk damaging the ancient plants and insects.

The researchers found that the fossils came from types of plants and insects that normally live in a rainforest. So, the fossils provide direct evidence that a rainforest existed in that area more than 10 million years ago.