Editing Cosmochemistry (section)

==Meteorites==
[[Meteorite]]s are one of the most important tools that cosmochemists have for studying the chemical nature of the Solar System. Many meteorites come from material that is as old as the Solar System itself, and thus provide scientists with a record from the early [[solar nebula]].<ref name=McSween/> [[Carbonaceous chondrite]]s are especially primitive; that is they have retained many of their chemical properties since their formation 4.56 billion years ago,<ref name=McSween2>{{cite journal| last=McSween| first=Harry| title=Are Carbonaceous Chondrites Primitive or Processed? A Review| journal=Reviews of Geophysics and Space Physics|date=August 1979| volume=17| issue=5| pages=1059–1078| doi=10.1029/RG017i005p01059 |bibcode = 1979RvGSP..17.1059M }}</ref> and are therefore a major focus of cosmochemical investigations.

The most primitive meteorites also contain a small amount of material (< 0.1%) which is now recognized to be [[presolar grain]]s that are older than the Solar System itself, and which are derived directly from the remnants of the individual supernovae that supplied the dust from which the Solar System formed. These grains are recognizable from their exotic chemistry which is alien to the Solar System (such as matrixes of graphite, diamond, or silicon carbide). They also often have isotope ratios which are not those of the rest of the Solar System (in particular, the Sun), and which differ from each other, indicating sources in a number of different explosive supernova events. Meteorites also may contain interstellar dust grains, which have collected from non-gaseous elements in the interstellar medium, as one type of composite [[cosmic dust]] ("stardust").<ref name="McSween"/>

Recent findings by [[NASA]], based on studies of [[meteorites]] found on [[Earth]], suggests [[DNA]] and [[RNA]] components ([[adenine]], [[guanine]], and related [[organic molecules]]), building blocks for life as we know it, may be formed extraterrestrially in [[outer space]].<ref name="Callahan">{{cite journal |last1=Callahan |first1 = M.P. |display-authors=2 |last2=Smith |first2=K.E. |last3=Cleaves |first3=H.J. |last4=Ruzica |first4=J. |last5=Stern |first5=J.C. |last6=Glavin |first6=D.P. |last7=House |first7=C.H. |last8=Dworkin |first8=J.P. |date=11 August 2011 |title=Carbonaceous meteorites contain a wide range of extraterrestrial nucleobases |doi=10.1073/pnas.1106493108 |pmid=21836052 |pmc=3161613 |volume=108 |issue = 34 |journal=Proc. Natl. Acad. Sci. U.S.A. |pages=13995–13998|bibcode = 2011PNAS..10813995C |doi-access = free }}</ref><ref name="Steigerwald">{{cite web |last=Steigerwald |first=John |title=NASA Researchers: DNA Building Blocks Can Be Made in Space |url=http://www.nasa.gov/topics/solarsystem/features/dna-meteorites.html |publisher=[[NASA]] |date=8 August 2011 |access-date=2011-08-10 |archive-date=2020-05-11 |archive-url=https://web.archive.org/web/20200511192941/https://www.nasa.gov/topics/solarsystem/features/dna-meteorites.html |url-status=dead }}</ref><ref name="DNA">{{cite web |title=DNA Building Blocks Can Be Made in Space, NASA Evidence Suggests |url=https://www.sciencedaily.com/releases/2011/08/110808220659.htm |date=9 August 2011 |website=[[ScienceDaily]] |access-date=2011-08-09}}</ref>