The oldest fossils are the remains of microscopic bacteria and algae from more than 3 billion years ago , called stromatolites.
Fossils are the object of study in Paleontology and can be of many types. The most famous are the remains of snails, bones or ammonoid transformed into stone. According to their visibility, they are distinguished into microfossils (visible under the light microscope), nanofossils (only visible under the electron microscope), and macro-fossils (those that can be seen with the naked eye).
On Earth there are certain places that stand out for the accumulation of fossils, such as the Solnhofen limestone or the strata with dinosaur remains from Patagonia. In Spain, Las Hoyas and Atapuerca stand out , the latter due to the abundant wealth of hominid fossils.
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