Most of the creatures today consist of hundreds of millions of cells, but when life on Earth first emerged, they were merely a few microns long, invisible to naked eyes.

According to a recent study published in the international journal Geology, scientists have found the secret behind it.

A joint study conducted by Chinese scientists and their British counterparts has confirmed that the critical evolution of "growing big" happened about 602 million years ago.

The Lantian biota, in today's Xiuning County, east China's Anhui Province, is believed to be the world's oldest known cluster of complex macroorganisms. The research team selected a 35-cm-long rock core from the stratum where the Lantian biota was located and found that the multicellular organisms first came into existence about 602 million years ago.

The early cluster of macroorganisms, preserved in black shales dating back to the Ediacaran Period, contains at least 18 different forms of multicellular creatures, said Yang Chuan, a researcher with the Institute of Geology and Geophysics, under the Chinese Academy of Sciences.

"The macroorganisms from the Lantian biota are still 'small' from today's perspective, as they are only a few centimeters long. But their evolution from micron-sized to centimeter-sized organisms is a giant leap in the evolutionary history of living creatures," Yang said.

During the Cambrian Explosion, some living creatures had grown up to 2 meters in length with more complex structures and functions, leading to the emergence of the ancestors of many modern organisms, Yang added.

The joint research was carried out by the Institute of Geology and Geophysics and the Nanjing Institute of Geology and Paleontology, both under the Chinese Academy of Sciences, the British Geological Survey and Durham University. (Xinhua)