What is the origin of life on Earth?


Criticism of Abiogenesis and Panspermia
A common criticism of abiogenesis is that there simply wasn't enough time on Earth for amino acids to develop into bacteria.
A common criticism of abiogenesis is that there simply wasn't enough time on Earth for amino acids to develop into bacteria.
©iStockphoto/Thinkstock

While the experiments carried out by Stanley Miller and others who have built upon his work show that life may have arisen from a primordial soup, that possibility remains theoretical. There is no evidence for pre-cellular life on Earth; what's more, critics of the RNA world hypothesis point out that the experiments that support the concepts were conducted with biologically created RNA. RNA can act as both a template for self-replication and an enzyme for carrying out that process, but these findings have been carried out in controlled laboratory experiments. This doesn't necessarily prove such delicate actions could happen in the seas of the ancient Earth.

For reasons like these, the RNA world hypothesis has been largely abandoned by proponents of abiogenesis in favor of other hypotheses, like the simultaneous development of both proteins and genetic templates or the development of life around undersea vents similar to those currently inhabited by today's extremophiles. But there is one criticism that any abiogenesis hypothesis has difficulty overcoming: time. DNA-based life is thought to have developed on Earth beginning around 3.8 billion years ago, giving pre-cellular life forms about 1 billion years to carry out random processes of encoding useful proteins and assembling them into the precursors of cellular life [source: Discovery News]. Critics of abiogenesis say that simply isn't enough time for inorganic matter to become the theorized precellular life. One estimate suggests it would take 10^450 (10 to the 450th power) years for one useful protein to be randomly created [source: Klyce].

This is one obstacle that makes panspermia an attractive explanation: It doesn't explain the origin of life, merely the origin of life on Earth. Panspermia hypotheses don't necessarily contradict abiogenesis; they merely shift the origin elsewhere. Yet the jury is still out on several important factors that must be in place for panspermia to be correct. Is it possible, for example, for microbial life to survive during the harsh conditions found in the trip through space, the entrance to Earth's atmosphere and the impact on Earth's surface?

Some recent hypotheses suggest that it needn't survive. One researcher postulates that dead scraps of DNA could have arrived on Earth via ballistic panspermia and were replicated through a kickstarted process similar to RNA world [source: Grossman]. Other researchers aim to scour Mars for fossil life and compare any genetic material to that found universally on Earth to determine relation [source: Chandler].

Yet if life on Earth did begin elsewhere and travel to our planet the question still remains: What is life's origin?

Related Articles

Sources

  • Abedon, Stephen T. "Germ theory of disease." The Ohio State University. March 28, 1998. (Accessed July 27, 2011.) http://www.mansfield.ohio-state.edu/~sabedon/biol2007.htm
  • Arizona State University. "Evidence of Martian life dealt a critical blow." Spaceflight Now. November 20, 2001. (Accessed July 27, 2011.) http://spaceflightnow.com/news/n0111/20marslife/
  • Boston, Penelope, PhD. "The search for extremophiles on Earth and beyond." Astrobiology web. 1999. (Accessed July 27, 2011.) http://www.astrobiology.com/adastra/extremophiles.html
  • Braeunig, Robert A. "Basics of space flight: orbital mechanics." Rocket and Space Technology. 2008. (Accessed July 26, 2011.) http://www.braeunig.us/space/orbmech.htm
  • Carnegie Institution. "Formaldehyde: poison could have set the stage for the origins of life." Science Daily. April 4, 2011. (Accessed July 27, 2011.) http://www.sciencedaily.com/releases/2011/04/110404151351.htm
  • Chandler, David L. "Are you a martian?" Massachusetts Institute of Technology. March 23, 2011. (Accessed July 26, 2011.) http://web.mit.edu/newsoffice/2011/martian-0323.html
  • Darwin, Charles. "The Origin of Species." Literature.org. (Accessed July 27, 2011.) http://www.literature.org/authors/darwin-charles/the-origin-of-species/introduction.html
  • Discovery News. "Life on Earth began three billion years ago." December 19, 2010. (Accessed July 27, 2011.) http://news.discovery.com/earth/life-began-3-billion-years-ago-dna-101220.html
  • Grossman, Lisa. "All life on Earth could have come from alien zombies." Wired. November 10, 2010. (Accessed July 27, 2011.) http://www.wired.com/wiredscience/2010/11/necropanspermia/
  • Klyce, Brig. "RNA world and other origin-of-life theories." Panspermia.org. (Accessed July 6, 2011.) http://www.panspermia.org/rnaworld.htm
  • Mount Desert Island Biological Laboratory. "Discovery places turtles next to lizards on family tree." EurekAlert. July 25, 2011. (Accessed July 25, 2011.) http://www.eurekalert.org/pub_releases/2011-07/mdib-dpt072511.php
  • Mullen, Leslie. "The three domains of life." NASA Astrobiology Institute. October 22, 2001. (Accessed July 28, 2011.) http://www.nai.arc.nasa.gov/news_stories/news_detail.cfm?ID=94
  • NASA. "Panspermia theoretically possible, say scientists." January 13, 2000. (Accessed July 26, 2011.) http://astrobiology.arc.nasa.gov/news/expandnews.cfm?id=295
  • NASA's Goddard Space Flight Center. "'Lost' Miller experiment gives pungent clue to origin of life." March 23, 2011. (Accessed July 27, 2011.) http://www.nasa.gov/centers/goddard/news/releases/2011/lost_exp.html
  • Nova. "How did life begin?" PBS. July 1, 2004. (Accessed July 27, 2011.) http://www.pbs.org/wgbh/nova/evolution/how-did-life-begin.html
  • O'Loughlin, Toni. "Number of Earth's species known to scientists rises to 1.9 million." The Guardian. September 29, 2009. (Accessed July 28, 2011.) http://www.guardian.co.uk/environment/2009/sep/29/number-of-living-species
  • Panspermia-Theory.com. "Panspermia and the origin of life on Earth." (Accessed May 23, 2011.) http://www.panspermia-theory.com/
  • Pickrell, John. "Humans, chimps not as close related as thought?" National Geographic News. September 24, 2002. (Accessed July 27, 2011.) http://news.nationalgeographic.com/news/2002/09/0924_020924_dnachimp.html
  • Pidwirny, Dr. Michael and Jones, Scott. "Biological classification of organisms." Fundamentals of Physical Geography, 2nd Edition. 2006. (Accessed July 27, 2011.) http://www.physicalgeography.net/fundamentals/9b.html
  • Schirber, Michael. "Meteorite-based debate over Martian life is far from over." Space.com. October 21, 2010. (Accessed July 28, 2011.) http://www.space.com/9366-meteorite-based-debate-martian-life.html
  • Science Daily. "Origin of life on Earth: scientists unlock mystery of molecular machine." May 1, 2009. (Accessed July 27, 2011.) http://www.sciencedaily.com/releases/2009/02/090219105324.htm
  • Science Daily. "Formaldehyde: poison could have set the stage for the origin of life." April 4, 2011. (Accessed July 27, 2011.) http://www.sciencedaily.com/releases/2011/04/110404151351.htm
  • Stubbs, Lisa. "How closely related are mice and humans? How many genes are the same?" Human Genome Project Information. May 17, 2011. (Accessed July 26, 2011.) http://www.ornl.gov/sci/techresources/Human_Genome/faq/compgen.shtml
  • Thompson, Andrea. "Oldest Mars meteorite younger then thought." Space.com. April 15, 2010. (Accessed July 27, 2011.) http://www.space.com/8229-oldest-mars-meteorite-younger-thought.html
  • Vaidya, Pushkar Ganesh. "Astrobiology: an overview." University of Mumbai. (Accessed May 23, 2011) http://www.astrobiology.co.in/Univ%20Mumbai%20Talk.ppt
  • Wade, Nicholas. "Tree of Life turns out to have surprisingly complex roots." New York Times. April 14, 1998. (Accessed July 27, 2011.) http://www.nytimes.com/1998/04/14/science/tree-of-life-turns-out-to-have-surprisingly-complex-roots.html?pagewanted=all&src=pm
  • Waggoner, Ben and Speer, B.R. "Introduction to the archaea: life's extremists." University of California, Berkeley. April 20, 2001. (Accessed July 27, 2011.) http://www.ucmp.berkeley.edu/archaea/archaea.html
  • Zimmer, Carl. "How and where did life on Earth arise?" Science. July 2005. (Accessed July 28, 2011.) http://www.sciencemag.org/content/309/5731/89.full

More to Explore