A University of Alberta-led research team has discovered that billions of years before life evolved in the oceans, thin layers of microbial matter in shallow water produced enough oxygen to support tiny, mobile life forms.
The researchers say worm-like creatures could have lived on the oxygen produced by photosynthetic microbial material, even though oxygen concentrations in the surrounding water were not high enough to support life. The research was conducted in shallow lagoons in Venezuela where the high salt content is comparable to oceans older than 500 million years.
The link between biomats and animals is demonstrated by the trace-fossil record, which are tracks left behind by the movements of the worm-like creatures. The trace-fossil records for these animals date to at least 555 million years ago.
These findings suggest that the appearance of animals was not dependent on an oxygenated ocean. Rather, the earliest animals could have live within photosynthetic biomats and derived life-sustaining oxygen from that source.
The most widely accepted date for the start of life on Earth is 700 to 600 million years ago when oxygen was produced in deep ocean water.
The researchers say their work opens the door to the search for life in early periods of the Earth's history when it was believed there was absolutely no oxygen and no chance of finding life.
The research was led by U of A geologist Murray Gingras and geomicrobiologist Kurt Konhauser. The research was published May 15 online in Nature Geoscience.
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