Phosphorus: You Can’t Have Life Without It, at Least on Earth
When searching for “carbon-based” life, we need to pay attention to other elements too.
What were the critical steps toward the first appearance of life on Earth? In a new paper published in Nature Chemistry, Clémentine Gibard and her co-authors from the Scripps Research Institute may have identified one of the most important ones: phosphorylation, or the addition of phosphate to another organic molecule. This is a critical process for biology on our planet, because all major building blocks of life contain phosphate groups, including ATP (the energy carrier of life), RNA, DNA, and cellular membranes.
Gibard and colleagues showed that a compound called diamidophosphate (DAP) can trigger the phosphorylation process in a simulated early Earth environment. They were able to produce nucleotides (building blocks of DNA and RNA), amino acids (building blocks of proteins), peptides (precursors of proteins), and lipid molecules that are essential to build cell walls. Phosphorylation is also essential for a variety of other cellular processes, such as signaling and the separation of DNA strands for replication.
Why is this important? Previously, there was no other molecule known to trigger all these key processes under environmental conditions thought to exist on early Earth. There is one remaining problem, however: How does DAP form in the first place? And would there be enough of it available on other planets? On Earth, phosphorus is a relatively rare compound, which is usually locked up in rocks as the mineral apatite. Only when surface rocks start weathering is the element set “free” to become available to life forms, most commonly in the form of phosphate.
However much exists on other worlds, there’s no question phosphorus is vital to life on Earth. It is the nutrient most highly valued by organisms, as well as the most recycled. Its ability to promote growth and reproduction is why it’s included in fertilizers. My own opinion is that life as we know it—including us—could be called phosphorus-based rather than carbon-based, because phosphorus is about 100 times more enriched than carbon in our bodies, compared to the background amounts of each element in the natural environment.