National Fossil Day takes place annually on 17 October. It was established in the United States to promote the scientific and educational values of fossils. A fossil is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in amber, hair, petrified wood, oil, coal, and DNA remnants. The totality of fossils is known as the fossil record. Paleontology is the study of fossils: their age, method of formation, and evolutionary significance. Specimens are usually considered to be fossils if they are over 10,000 years old. The oldest fossils are from around 3.48 billion years old to 4.1 billion years old. The observation in the 19th century that certain fossils were associated with certain rock strata led to the recognition of a geological timescale and the relative ages of different fossils. The development of radiometric dating techniques in the early 20th century allowed scientists to quantitatively measure the absolute ages of rocks and the fossils they host.
There are many processes that lead to fossilization, including permineralization, casts and molds, authigenic mineralization, replacement and recrystallization, adpression, carbonization, and bioimmuration. Fossils vary in size from one micrometer bacteria to dinosaurs and trees, many meters long and weighing many tons. A fossil normally preserves only a portion of the deceased organism, usually that portion that was partially mineralized during life, such as the bones and teeth of vertebrates, or the chitinous or calcareous exoskeletons of invertebrates. Fossils may also consist of the marks left behind by the organism while it was alive, such as animal tracks or feces (coprolites). These types of fossil are called trace fossils or ichnofossils, as opposed to body fossils. Some fossils are biochemical and are called chemofossils or biosignatures.
National Fossil Day was first held on October 13, 2010, during Earth Science Week. The National Park Service and over 270 partners, including museums, institutions, organizations and other groups, joined together to educate the public about the value of fossils. Hundreds of activities were hosted across the United States aimed at improving public understanding of the world’s fossil heritage. The second National Fossil Day was observed on October 12, 2011 with events at museums, parks, universities, and non-profit organizations. National Fossil Day 2012 was celebrated on October 17, 2012 with an opening event held on the National Mall in Washington, D.C.. Similar events have been held annually.
Each year a new educational National Fossil Day logo is created and announced in mid-January on the event website, depicting a prehistoric organism. The original National Fossil Day logo in 2010 and featured a fossil titanothere, a prehistoric mammal. In 2011, a marine reptile, the mosasaur, was used. For 2012, the mammoth was used for the annual logo. For 2013, a Paleozoic invertebrate known as the eurypterid was featured. For 2014 a fossil of an aetosaur, a Triassic reptile, was used.For 2015, a large herbivore mammal known as a chalicothere was used. For 2016, the prehistoric saber-toothed cat Smilodon fatalis was used For 2017, a jawless fish known as a heterostracan was used.