I have a fondness for graphs, especially ones that let you survey the sweep of life’s history in one glance. Here’s a new one, out today in the journal Science. It’s the latest look at the levels of biodiversity over the past half billion years. Scientists crunched the numbers on about 3.5 million fossils of ocean-dwelling invertebrates, using more detailed data than in previous surveys. (Some marine invertebrates leave fabulous heaps of fossils. Other species, like our own, are more delicate.) The horizontal axis marks time, and the vertical one marks the number of genera alive at any particular interval of about 10 million years. (Genera are groups of species. The genus Homo includes us, Neanderthals, and