Fossils from Llanginog Bay, South Wales, have been dated with unprecedented precision. Because these fossils are among the earliest examples of large multicellular life and match fossils from other parts of the world, this dating helps narrow down when life evolved from something we can barely see to a variety of complex life.

As humanity explores more worlds, we may learn that what makes Earth unique is not the existence of life, but the existence of complex multicellular life. After all, life appeared on Earth when the planet cooled enough, which suggests that it wasn’t that difficult to achieve. Multicellular life emerged three and a half billion years later.

If so, the so-called Avalon Cluster, in which large, interesting creatures begin to appear in fossils all over the planet, could be one of the extraordinary events not only of Earth but of the galaxy as well. New research has helped clarify when this happens and some of the reasons why.

“These creatures are somewhat similar to modern marine species such as jellyfish, but they are also strange and unusual. Some look like ferns, some look like cabbages, some look like sea plumes,” said Curtin University PhD student Anthony Clark.

We found almost no gradual prerequisites for this abundance. Not long ago, the only living things that could be seen without a microscope were colonies of small organisms such as stromatolites. Relatively simple disks and microbial clusters appeared in deeper waters a few million years ago, but then suddenly Avalon species appeared at similar times in different parts of the world.

This makes the timing of this event important if we want to know what caused it. The maximum age of such fossils has been found at 564.13 ± 0.65 million years ago, but by themselves we cannot say whether they are the first.

Carbon dating cannot determine a period this old. The layers where these fossils were found and known as the Ediacaran biota, because of the hills where they were first found, generally do not have a good alternative. But sometimes volcanic eruptions help. Ash layers can be dated much more precisely, and if they lie above or below a fossil bed (or preferably both), we have a much better idea of ​​its time.

The volcanic formation is located in the center of the Lyanginog depression. Zircon crystals and rutile, preferred by geologists for their ease of dating, are found in layers containing Ediacaran fossils. By dating both crystals, Clarke and colleagues obtained a date of 564.09 ± 0.70 million years ago, confirming that these species developed in different parts of the world in recent periods.

“These fossils were found in the late 1970s and have not been dated. We are using exciting techniques that can be applied to small exposures.”

Although Clark acknowledges that the characteristics of the fossils are very different, the more places we find similar dates for similar fossils, the more certain we can be that they appeared and disappeared almost simultaneously.

Clark notes that these dates indicate that the emergence of these relatively large, complex species occurred soon after the end of the Snow World period, when nearly the entire planet was covered in ice. The reason for the sudden development of these life forms is suggested to be the flood of nutrients dragged into the oceans by glaciers eroding rocks.

But Clark says that wasn’t the only thing going on at the time. “There has been a huge change in ocean chemistry,” he told IFLScience. “Iron levels dropped and oxygen levels increased. There were also changes in continental thrust. Some researchers suggest this is linked [з біологічним розвитком]. At the time, Britain was close to the equator and drifting northward. There was a chain of volcanic islands spewing zircons into the atmosphere, and luckily it rained, allowing us to determine when the species went extinct. “The deaths were probably related to the gases released by these explosions.”