Life is primarily composed of a select set of elements that are considered necessary to sustain life: carbon, hydrogen, nitrogen, oxygen, phosphorous, and sulfur. With nitrogen composing approximately 78% of our atmosphere; oxygen and hydrogen, in the form of water, covering 71% of Earth’s surface; and carbon, phosphorous, and sulfur filling the sediments of our planet, it is is easy to understand how life on Earth evolved to rely on these six elements (Louviere, 2006; USGS 2015).
Scientists also search for life in seemingly inaccessible places, such as planets over fifty light years away; their searches begin with the same six basic elements. We assume that we can apply Earth’s chemical principles to distant planets, but is this rational or are we comparing apples to oranges?
The concept of biomolecular substitutions is so rare and unfamiliar, yet we have found it here on our own Earth. Another element we associate with life is iron, which is a fundamental constituent of the hemoglobin in blood and contributes to its red coloration.
Despite this, researchers have found a small number of species with blue blood that uses copper and hemocyanin in lieu of iron and hemoglobin. The most noteworthy example of this inconsistency is the horseshoe crab, whose blood is also being researched for possible biomedical applications (MarineBio 2013).* If a substitution as drastic as this can occur, what other hidden anomalies lie in the depths of our oceans or corners of the rainforests?
Felisa Wolfe-Simon, an astrobiologist of the National Aeronautical Space Administration (NASA), released information in 2010 of another life form that she believes can perform a profound substitution—Halomonas sp. Strain GFAJ-1. Wolfe-Simon has claimed that this extremophillic bacterium found in Mono Lake, California can substitute arsenate for phosphate in its DNA (Wolfe-Simon 2011). Soon after publication, her research sparked controversy and debate in the scientific community as it had generally been accepted that DNA structure is universal to all organisms.
Upon reevaluating this conception, I took a personal interest in this bacterium and how it is able to utilize a toxic substance in a molecule that executes nearly all biological functioning. I pursued this curiosity in GFAJ-1 and applied various scientific techniques in order to characterize its DNA. Upon completion, I discovered that arsenate is actually incorporated into the DNA structure, thus supporting Wolfe-Simon’s controversial conclusions.
This information leaves us with skepticism about the world around us, but promise in the field of astrobiology. Now when searching for life on other planets, we cannot limit our searches to the original six elements stated; we must embrace this newfound knowledge and evolve with the Earth and our discoveries.
*Read more about the medicinal uses of the horseshoe crab here: http://www.pbs.org/wnet/nature/crash-a-tale-of-two-species-the-benefits-of-blue-blood/595/.
Editor: Shreya Singireddy