Early Plants Grew Big to Colonize Earth, Study Finds

Artist’s impression of rangeomorphs, fern-like organisms that lived during the Ediacaran Period. (Charlotte Kenchington)

(CN) – Organisms on Earth about 600 million years ago did not suddenly grow large because they were fighting for more food, but because they were trying to propel their offspring farther into the world.

Research suggests real estate was a prime driver in the first expansion of complex organisms on Earth, according to a study by the University of Cambridge released Monday.

Between 635 and 541 million years ago, life on earth was microscopic. But during the Ediacaran Period the first complex organisms began to appear on the ocean floor.

Long before any life could crawl, walk, fly or swim there were stationary rangeomorphs, which resembled a plant frond with stem-like structures that are believed to have gathered nutrients from the water around them.

One hypothesis is competition in the frond community led to innovations with rangeomorphs’ stems and they outgrew the rest of the microscopic life around them. Rangeomorph fossils show that some of the largest organisms grew to at least 6 feet tall.

But the new study, titled “Why Life on Earth First Got Big,” says rangeomorphs got big to spread their offspring as far as possible.

Researchers based their findings on a bedding plane – layers of compressed rock – located in Newfoundland, Canada, where some of the oldest known macro fossils from this period are found in the world.

Previous theories held that competition for food drove the rangeomorphs’ exponential growth in size. Plants and trees in modern forests compete for light, with larger trees crowding out smaller ones.

“We wanted to know whether there were similar drivers for organisms during the Ediacaran Period,” said lead author Emily Mitchell of Cambridge’s Department of Earth Sciences. “Did life on Earth get big as a result of competition?”

Ediacaran organisms, like the rangeomorphs, were stationary on the ocean floor and gathered food from the water around them with stems that grew from their fronds. But the researchers believe the rangeomorphs’ stems were also used to send their offspring out to colonize the world around them.

Dr Charlotte Kenchington from Memorial University of Newfoundland in Canada co-wrote the study, which will be published in the journal Nature Ecology and Evolution.

Rangeomorphs and other Ediacaran organisms faded away at the beginning of the Cambrian Period, an era of a rapid evolutionary development about 541 million years ago.

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