Up to now, conventional scientific wisdom held that the planet was populated only by single-celled microbes until the so-called Cambrian explosion, a major surge of biodiversity that began some 600 million years ago.
Ever-more complex life forms emerged rapidly from there, eventually creating an evolutionary tree with homo sapiens atop one of its branches.
But the new organism, which appears to have lived in colonies, shows that the drive toward complexity began much sooner.
Shaped like cookies with ragged edges and a lumpy interior, more than 250 specimens have been found so far, varying in size and different body shapes from one to 12 centimetres.
The fossilised creatures may also have crossed another threshold of evolution far earlier than any other known organism.
Unlike simple bacteria, their cells appear to have membrane-bound nucleus housing and protecting its chromosomes, the genetic blueprints for life.