Amber is a very ancient tree resin produced by long extinct trees, entirely organic, whose composition has changed little over millions of years. Resin is exuded by both conifer trees and tropical broad-leaved trees as a form of defense against insects and disease. Tropical living relatives of the amber trees produce large quantities of resin possibly due to the more intensive insect attacks in the tropics. Trees also produce resin flows to seal breaks in their bark or to seal off broken branches. The resin covers the breaks in the bark and hardens acting as a seal against further damage by insects or fungi. Before the resin hardens, small insects, plant debris, small vertebrates become trapped in the sticky substance and eventually become 'ambalmed'. The resin eventually becomes mixed with the soil when it falls off the tree or when the tree dies and falls to the forest floor becoming part of the sediments, where over millions of years the resin's terpenes become linked and the resin becomes amber.

Dominican Republic amber has been dated in scientific papers and the popular press as being between 15 million years to 40 million years old (Lower Miocene to Lower Oligocene) but the current evidence suggests a Lower to Middle Miocene age.