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Aliens on Earth?

The #arseniclife Affair


Annie Prud’homme-Genereux
Continuing Studies and Executive Education
Capilano University


The discovery of a bacterium capable of substituting arsenic for phosphorus in its DNA was announced with much fanfare in 2010. It was immediately and very publicly critiqued by researchers posting their analyses of the paper on their blogs. The authors of the original finding refused to respond to the critiques in a public forum, arguing that peer review is the proper channel for such debates. This interrupted case investigates the evidence for and against "arsenic life" and uses Twitter and blog posts from the controversy to question the proper forum for critiquing science. The case was written for first-year biology students in an introductory biology course and has also been used in a third-year astrobiology course. It is used following a discussion of "What is life?" and as an introduction to the major biomolecules (DNA, RNA, amino acids, proteins, phospholipids, and ATP).  Students should have some familiarity with biomolecules and a basic (high school level) understanding of chemistry.


  • Define shadow life, explain its origins, describe possible forms and how they may be searched for, and discuss the implications of finding an example of shadow life.
  • Describe why researchers looked for arsenic life.
  • Critically evaluate the strength of the evidence for and against arsenic life (i.e., the claim that bacteria from Mono Lake can grow using arsenic instead of phosphorus and incorporate that atom into its DNA).
  • Appraise the strengths and weaknesses of the scientific peer review process, choose and defend the forum (peer review or public) researchers ought to use in critiquing one another's work, and evaluate the actions and decisions of key players in the arsenic life debate.


Astrobiology; origin of life; weird life; alternate life; alien life; phosphate; DNA; arsenic; arsenic DNA; extremophile; limits of life; peer review; scientific publishing; scholarly communication; NASA

Topical Areas

Scientific method, Science and the media, Scientific argumentation

Educational Level

Undergraduate lower division, Undergraduate upper division, Graduate



Type / Methods

Discussion, Interrupted, Journal Article



Subject Headings

Biology (General)  |   Evolutionary Biology  |   Microbiology  |   Molecular Biology  |   Chemistry (General)  |   Biochemistry  |   Organic Chemistry  |   Interdisciplinary Sciences  |   Journalism  |  

Date Posted


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