You know about fossils, but what other secrets are lurking in the ground beneath our feet?

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Sources:
http://rstb.royalsocietypublishing.org/content/370/1660/20130383#ref-83
http://www.nature.com/nature/journal/v506/n7486/full/nature12921.html
http://www.pnas.org/content/106/52/22352.full#sec-8
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https://www.ncbi.nlm.nih.gov/pmc/articles/PMC140122/
http://www.sciencedirect.com/science/article/pii/S1164556303000335
http://www.sciencedirect.com/science/article/pii/016770128790025X
http://science.sciencemag.org/content/300/5620/791
https://academic.oup.com/mbe/article/24/4/982/1012556/Ancient-DNA-Chronology-within-Sediment-Deposits?ijkey=bc3552daa5b361e4213c0fb839987c51d731a0c4&keytype2=tf_ipsecsha
http://science.sciencemag.org/content/347/6225/998.full?sid=a8020087-b772-4cc8-a69b-65ad52f2cfbc
https://elifesciences.org/content/4/e10005
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Images:
https://commons.wikimedia.org/wiki/File:Greenland_eastcoast.jpg
https://commons.wikimedia.org/wiki/File:EscherichiaColi_NIAID.jpg
https://commons.wikimedia.org/wiki/File:PCR_tubes.png
https://commons.wikimedia.org/wiki/File:Quebrada_de_Cafayate,_Salta_(Argentina).jpg
https://commons.wikimedia.org/wiki/File:Wheat_harvest.jpg
https://www.nasa.gov/feature/jpl/mars-rock-ingredient-stew-seen-as-plus-for-habitability