Editing Atom (section)

=== Earth ===
Most of the atoms that make up the [[Earth]] and its inhabitants were present in their current form in the [[nebula]] that collapsed out of a [[molecular cloud]] to form the [[Solar System]]. The rest are the result of radioactive decay, and their relative proportion can be used to determine the [[age of the Earth]] through [[radiometric dating]].<ref name=Manuel2001pp511-519>[[#refManuel2001|Manuel (2001). ''Origin of Elements in the Solar System'', pp. 40–430, 511–519]]</ref><ref name=gs190_1_205 /> Most of the [[helium]] in the crust of the Earth (about 99% of the helium from gas wells, as shown by its lower abundance of [[helium-3]]) is a product of [[alpha decay]].<ref name=anderson_foulger_meibom2006 />

There are a few trace atoms on Earth that were not present at the beginning (i.e., not "primordial"), nor are results of radioactive decay. [[Carbon-14]] is continuously generated by cosmic rays in the atmosphere.<ref name=pennicott2001 /> Some atoms on Earth have been artificially generated either deliberately or as by-products of nuclear reactors or explosions.<ref name=yarris2001 /><ref name=pr119_6_2000 /> Of the [[Transuranium element|transuranic elements]]—those with atomic numbers greater than 92—only [[plutonium]] and [[neptunium]] occur naturally on Earth.<ref name=poston1998 /><ref name=cz97_10_522 /> Transuranic elements have radioactive lifetimes shorter than the current age of the Earth<ref>{{cite book|last1=Zaider|first1=Marco|last2=Rossi|first2=Harald H.|year=2001|title=Radiation Science for Physicians and Public Health Workers|publisher=Springer|isbn=978-0-306-46403-4|oclc=44110319|page=[https://archive.org/details/radiationscience0000zaid/page/17 17]|url=https://archive.org/details/radiationscience0000zaid/page/17}}</ref> and thus identifiable quantities of these elements have long since decayed, with the exception of traces of [[plutonium-244]] possibly deposited by cosmic dust.<ref name=Manuel2001pp511-519 /> Natural deposits of plutonium and neptunium are produced by [[neutron capture]] in uranium ore.<ref name=ofr_cut />

The Earth contains approximately {{val|1.33|e=50}} atoms.<ref name=weisenberger /> Although small numbers of independent atoms of [[noble gas]]es exist, such as [[argon]], [[neon]], and [[helium]]<!-- note that noble gases exist not only in the atmosphere -->, 99% of [[Earth's atmosphere|the atmosphere]] is bound in the form of molecules, including [[carbon dioxide]] and [[Diatomic molecule|diatomic]] [[oxygen]] and [[nitrogen]]. At the surface of the Earth, an overwhelming majority of atoms combine to form various compounds, including [[water]], [[salt]], [[silicate]]s, and [[oxide]]s. Atoms can also combine to create materials that do not consist of discrete molecules, including [[crystal]]s and liquid or solid [[metal]]s.<ref name=pidwirnyf /><ref name=pnas99_22_13966 /> This atomic matter forms networked arrangements that lack the particular type of small-scale interrupted order associated with molecular matter.<ref>{{cite book
|last=Pauling|first=Linus|year=1960
|title=The Nature of the Chemical Bond
|publisher=Cornell University Press
|isbn=978-0-8014-0333-0
|oclc=17518275|pages=5–10}}</ref>