Washington, March 27 : An International team of scientists have discovered that a deficiency of oxygen and the heavy metal molybdenum in the ancient deep ocean may have delayed the evolution of animal life on Earth for nearly 2 billion years.
The study was led by Clint Scott, a graduate student at University of California Riverside (UCR), along with Timothy Lyons, a professor of biogeochemistry at UCR and Ariel Anbar, an associate professor at Arizona State University.
According to Anbar, "Tim and I have suspected for a while that if the oceans at that time were oxygen deficient, they should also have been deficient in molybdenum. We've found evidence of that deficiency before, at a couple of particular points in time."
"The new data are important because they confirm that those points were typical for their era," he added.
Molybdenum was important for the study because it is used by some bacteria to convert the element nitrogen from a gas in the atmosphere to a form useful for living things - a process known as "nitrogen fixation."
"The amount of molybdenum in the ocean probably played a major role in the development of early life," said Lyons.
Bacteria cannot fix nitrogen efficiently when they are deprived of molybdenum. And if bacteria can't fix nitrogen fast enough, then eukaryotes - a kind of organism that includes plants, pachyderms and people - are in trouble because eukaryotes cannot fix nitrogen themselves at all.
"So, if bacteria were struggling to get enough molybdenum, there probably wouldn't have been enough fixed nitrogen for eukaryotes to flourish," said Anbar.
According to Lyons, "These molybdenum depletions may have retarded the development of complex life such as animals for almost two billion years of Earth history."
The research was motivated by a review article by Anbar and Andy Knoll, a colleague at Harvard University.
Knoll was perplexed by the fact that eukaryotes didn't dominate the world until around 0.7 billion years ago, even though they seemed to have evolved before 2.7 billion years ago.
Together, Anbar and Knoll postulated that molybdenum deficiency was the key, arguing that the metal should have been scarce in ancient oceans because there was so little oxygen in the atmosphere in those times.