Editing Hydrogen (section)

===Terrestrial===
Hydrogen is the third most abundant element on the Earth's surface,<ref name="ArgonneBasic">{{cite journal
|author=Dresselhaus, M.
|author-link=Mildred Dresselhaus
|display-authors=etal
|date=15 May 2003
|url=http://www.sc.doe.gov/bes/hydrogen.pdf
|title=Basic Research Needs for the Hydrogen Economy
|journal=APS March Meeting Abstracts
|volume=2004
|pages=m1.001
|publisher=Argonne National Laboratory, U.S. Department of Energy, Office of Science Laboratory
|access-date=5 February 2008
|archive-url=https://web.archive.org/web/20080213144956/http://www.sc.doe.gov/bes/hydrogen.pdf
|archive-date=13 February 2008
|bibcode=2004APS..MAR.m1001D
}}</ref> mostly in the form of [[chemical compound]]s such as [[hydrocarbon]]s and water.<ref name="Miessler">{{cite book|first1=G. L.|last1=Miessler|last2=Tarr|first2=D. A.|date=2003|title=Inorganic Chemistry|edition=3rd|publisher=Prentice Hall|isbn=978-0-13-035471-6|url-access=registration|url=https://archive.org/details/inorganicchemist03edmies}}</ref>  Elemental hydrogen is normally in the form of a gas, {{chem2|H2}}. It is present in a very low concentration in Earth's atmosphere (around 0.53 [[part per million|ppm]] on a molar basis<ref name="Grinter">{{cite journal |last1=Rhys Grinter |last2=Kropp |first2=A. |last3=Venugopal |display-authors=etal |date=2023 |title=Structural basis for bacterial energy extraction from atmospheric hydrogen |journal=Nature |volume=615 |issue=7952 |pages=541–547 |bibcode=2023Natur.615..541G |doi=10.1038/s41586-023-05781-7 |pmc=10017518 |pmid=36890228}}</ref>) because of its light weight, which enables it to [[atmospheric escape|escape the atmosphere]] more rapidly than heavier gases. Despite its low concentration in our atmosphere, terrestrial hydrogen is sufficiently abundant to support the metabolism of several bacteria.<ref>{{cite journal |doi=10.1042/BST20230120 |title=Developing high-affinity, oxygen-insensitive &#91;NiFe&#93;-hydrogenases as biocatalysts for energy conversion |date=2023 |last1=Greening |first1=Chris |last2=Kropp |first2=Ashleigh |last3=Vincent |first3=Kylie |last4=Grinter |first4=Rhys |journal=Biochemical Society Transactions |volume=51 |issue=5 |pages=1921–1933 |pmid=37743798 |pmc=10657181 }}</ref>

Large underground deposits of hydrogen gas have been discovered in several countries including [[Mali]], [[France]] and [[Australia]].<ref name="Pearce-2024">{{Cite web |last=Pearce |first=Fred |date=January 25, 2024 |title=Natural Hydrogen: A Potential Clean Energy Source Beneath Our Feet |url=https://e360.yale.edu/features/natural-geologic-hydrogen-climate-change |access-date=2024-01-27 |website=[[Yale Environment 360|Yale E360]] |language=en-US}}</ref> As of 2024, it is uncertain how much underground hydrogen can be extracted economically.<ref name="Pearce-2024" />