Five hundred and fifty million years ago, the earth looked nothing like it does today. Oceans covered almost the entire earth, and for the most part, all life was invisible—just tiny photosynthetic microbes floating around, eating, reproducing, and dying. So why did any living thing ever get any bigger than that, to the point that we had 85-foot-long dinosaurs and dragonflies 2.5 feet wide?
Close to the ocean floor around that time, a remarkable living thing was emerging. They looked like ribbed leaves, but they might as well have been growing out of some extraterrestrial ocean floor, like Europa, because they’re nothing like plants or fungi on earth today. The cells on these mighty plants could savagely swallow amoebas and microbes whole. Although they were just under three inches tall, these organisms were titans compared to the microbes that swarmed around them. These were the first multicellular organisms on earth.
Over the past several hundred million years, multicellular life has proliferated on earth. Important examples include, well, humans, and just about everything else you see every day. But until now, scientists have had a hard time figuring out what spurred life to develop into complex, multicellular systems—giants, compared to their microbial counterparts. But research published in Nature Ecology and Evolution on Monday may have the answers.
Authors Emily Mitchell and Charlotte Kenchington assert that life didn’t become huge in an attempt to monopolize the food on the seafloor, like different species of trees do today. Rather, the strategy of these life forms was to dominate the seafloor by spreading over a wide area. By anchoring themselves to the floor and towering above other bottom-dwellers, they could release sex cells at a greater height and spread over a larger area. In essence, they wanted to cultivate a vast community along the bottom of the ancient ocean.
In a phone call with The Outline, Mitchell said that these organisms—which hail from what’s known as the Ediacaran period (pronounced Eddie-AH-kirin)—predate intuitive concepts in nature like predation, and defy the logic we’re familiar with in ecosystems like forests.
“It’s really exciting because these [Ediacarans] are the first large things,” Mitchell said. “These are almost certainly our oldest ancestors, but we don’t know anything about them.”
Mitchell, who comes from a mathematical background, said that she and Kenchington were able to draw these conclusions about Ediacaran life by deciphering the patterns of these organisms on the ocean floor, as preserved in fossils. By doing this, they were able to disprove that Ediacaran life was competing for food—a longstanding idea in paleontology.
“If things are competing for local resources—such as food—they tend to space out from each other, that’s because the larger you are, the more resources you need,” Mitchell said. “What I found is that the really big [organisms] didn’t need to compete for food because there was plenty to go around.”
The Ediacaran period was incredibly unique in Earth’s history. About 200 million years earlier (seven hundred million years ago), the earth was in a “snowball” state, covered with ocean water that—due to a combination of natural climatic forces—was almost entirely frozen. A small patch of open water around the equator was the only respite from the glacial hellscape. It was the only source of sunlight for the microscopic organisms that represented the breadth of life on earth.
Then, just over a hundred million years later, as the ice naturally melted and the waters opened up, allowing these first multicellular organisms emerge. Multicellular Ediacaran organisms are far from being analogs to life on earth as we know it today—but for paleontologists, that’s part of the excitement.
“For me, it’s wonderful having this incredible dataset—we have surfaces with thousands and thousands of fossils because they didn’t move around and they were killed by volcanic ash, rather like Pompeii,” Mitchell said. “The entire community is captured, so you can use all of these mathematical techniques to actually figure out what’s going on.”