Evidence left at the crime scene is abundant and global: Fossil remains show that sometime around 252 million years ago, about 90 percent of all species on Earth were suddenly wiped out — by far the largest of this planet’s five known mass extinctions. But pinpointing the culprit has been difficult, and controversial. Now, a team of NAI-funded researchers at MIT may have found enough evidence to convict the guilty parties — but you’ll need a microscope to see the killers. https://astrobiology.nasa.gov/articles/2014/4/9/microbial-innovation-causes-the-end-permian-extinction/