The only way to learn about life that went extinct thousands, millions, and billions of years ago is to study the fossils they left behind in rocks. Fossils are the key to understanding what organisms lived on Earth long before modern humans appeared. Fossils are like windows to the past.

Definitionthe process when organic material (bones, shells, leaves) is turned into stone
Name Origin: from the Latin word fossilis, which translates into "something dug up"
Researcher: German physician Georgius Agricola first used the term "fossil" in his book, The Nature of Fossils, published in 1546
Significance: Fossils are the key to understanding life in the past.

Image credits: main image: courtesy of USGS.