Earth’s First Animals Barely Needed Any Oxygen
by George Dvorsky
There’s a longstanding theory which says oxygen-rich oceans were a key requirement for complex life to emerge on Earth. But a new study involving sea sponges upsets this notion, showing that primitive animals may have been able to survive with hardly any oxygen at all.
The first microbes appeared on Earth about 3.6 billion years ago, but it took an exceptionally long time for complex multicellular life to emerge — another three billion years. Perhaps not coincidentally, this also happened to be the time when levels of oxygen in the atmosphere escalated to present day concentrations of about 20%. Many scientists have thus concluded that animals needed the higher levels to survive, thrive, and evolve.
But a new study by Daniel Mills of the University of Southern Denmark in Odense suggests this may not be the case. By studying modern breadcrumb sponges, Mills has threatened this assumption, while simultaneously strengthening another.
200 Times Less…
Sea sponges may not seem animal-like, but they are among the planet’s earliest animals. They’re always multicellular and they grow from an embryo. They’ve also got complex physiological structures, including a network of channels that help draw food and water through their bodies. And based on the paleontological evidence, modern sea sponges aren’t too far removed from their ancient brethren…
(read more: io9)
* Read the entire study at PNAS: “The oxygen requirements of the earliest animals.”
Image: Top: Don Dixon/Cosmographica; Mills/PNAS.