Scientists have discovered fossil remains of sponge-like structures within ancient reefs that may have lived in the oceans up to 890 million years ago, an advance that may push back earliest evidence of animal life on Earth by over 350 million years.
According to the scientists, including Elizabeth Turner from the Laurentian University in Canada, the findings, if verified, could change our understanding of the evolution of animal life on the planet.
Sponges are one of the earliest animals that emerged on the Earth, and are multicellular organisms with simple bodies full of pores and channels allowing water to circulate through them.
While genetic evidence from modern sponges, such as the ones used to make bath sponges, have indicated that these marine creatures emerged during the early Neoproterozoic era 1,000–541 million years ago, the scientists say fossilised sponge bodies from this period have been lacking.
In the current study, published in the journal Nature, Turner and her colleagues examined rock samples from 890 million-year-old reefs in northwestern Canada that were built by calcium-carbonate-depositing bacteria.
In these samples, the researchers found branching networks of tube-shaped structures that contained, and were surrounded by, crystals of the mineral calcite.
On closer examination, the scientists found that the structures resemble the fibrous skeleton found within hornysponges — a type of sponge used to make commercial bathsponges.
They also resembled “structures previously identified in calcium carbonate rocks that are thought to have been created by the decay of hornysponge bodies,” the researchers noted in a statement.
Based on the analysis, the scientists believe the newly discovered fossil may be remains of hornysponges that lived about 90 million years at a time before the Earth’s oxygen levels increased to levels necessary to support animal life.
If the findings are validated, the scientists believe the study could prove that the evolution of early animals occurred independently of this oxygenation event, and that early animal life survived the severe ice ages between 720 and 635 million years ago.
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