Two lifeforms merge into one organism in 'once-in-a-billion-year' event

Two lifeforms have merged into a single organism for the first time in a billion years. In two recent papers, an international team of scientists described the first known nitrogen-fixing organelle within an eukaryotic cell through the process called primary endosymbiosis. "A billion years ago or so, it happened with the chloroplast, and that gave us plants," a scientist said.