User:7h3 3L173/Mr. Funtestpage/Draft (NAGH)

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Pre-Cambrian stromatolites in the Siyeh Formation, Glacier National Park. In 2002, William Schopf of UCLA published a paper in the scientific journal Nature arguing that geological formations such as this possess 3.5 Ga (billion years old) fossilized cyanobacteria microbes. If true, they would be the earliest known life on earth.

In the natural sciences, abiogenesis is either the concept that life on Earth arose from inanimate matter, or the study thereof. It also has a now outdated meaning akin to spontaneous generation. The theory of abiogenesis states that life originated through the 'evolution' of complex molecules (so-called "chemical evolution"). Amino acids, often called "the building blocks of life", occur naturally, due to chemical reactions unrelated to life. In all living things, these amino acids are organized into proteins, and the construction of these proteins is mediated by nucleic acids. Thus the question of how life on Earth originated is a question of how the first nucleic acids arose.

Some facts about the origin of life are well understood, others are still the subject of current research. The first living things on Earth are thought to be single cell prokaryotes. The oldest ancient fossil microbe-like objects are dated to be 3.5 Ga (billion years old), just a few hundred million years younger than Earth itself.[1][2] By 2.4 Ga, the ratio of stable isotopes of carbon, iron and sulfur shows the action of living things on inorganic minerals and sediments[3][4] and molecular biomarkers indicate photosynthesis, demonstrating that life on Earth was widespread by this time.[5][6]

On the other hand, the exact sequence of chemical events that led to the first nucleic acids is not known. Several hypotheses about early life have been proposed, most notably the iron-sulfur world theory (metabolism without genetics) and the RNA world hypothesis (RNA life-forms).

  1. ^ Wilde SA, Valley JW, Peck WH, Graham CM (2001). "Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago". Nature. 409 (6817): 175–8. PMID 11196637. doi:10.1038/35051550.  Unknown parameter |month= ignored (help)
  2. ^ Schopf JW, Kudryavtsev AB, Agresti DG, Wdowiak TJ, Czaja AD (2002). "Laser--Raman imagery of Earth's earliest fossils". Nature. 416 (6876): 73–6. PMID 11882894. doi:10.1038/416073a.  Unknown parameter |month= ignored (help)
  3. ^ Hayes, John M. (2006). "The carbon cycle and associated redox processes through time". Phil. Trans. R. Soc. B. 361 (1470): 931–950. doi:10.1098/rstb.2006.1840.  Unknown parameter |coauthors= ignored (|author= suggested) (help)
  4. ^ Archer, Corey (2006). "Coupled Fe and S isotope evidence for Archean microbial Fe(III) and sulfate reduction". Geology. 34 (3): 153–156. doi:10.1130/G22067.1.  Unknown parameter |coauthors= ignored (|author= suggested) (help)
  5. ^ Cavalier-Smith, Thomas (2006). "Introduction: how and when did microbes change the world?". Phil. Trans. R. Soc. B. 361 (1470): 845–850. doi:10.1098/rstb.2006.1847.  Unknown parameter |coauthors= ignored (|author= suggested) (help)
  6. ^ Summons, Roger E. (2006). "Steroids, triterpenoids and molecular oxygen". Phil. Trans. R. Soc. B. 361 (1470): 951–968. doi:10.1098/rstb.2006.1837.  Unknown parameter |coauthors= ignored (|author= suggested) (help)