Scientists paint new picture of Earth's ancient ocean chemistry

Washington, Feb 12 (ANI): In a new research, a team of scientists has developed a detailed and dynamic three-dimensional model of Earth's early ocean chemistry that can significantly advance our understanding of how early animal life evolved on the planet.

The team was led by biogeochemists at the University of California, Riverside.

Working on rock samples from the Doushantuo Formation of South China, one of the oldest fossil beds and long viewed by paleontologists to be a window to early animal evolution, the research team is the first to show that Earth's early ocean chemistry during a large portion of the Ediacaran Period (635 - 551 million years ago) was far more complex than previously imagined.

Their work is the first comprehensive geochemical study of the Doushantuo Formation to investigate the structure of the ocean going from shallow to deep water environments.

It is also one of the most comprehensive studies for any Precambrian interval.

The researchers' model for the ancient ocean argues for a stratified marine basin, one with a chemically layered water column.

While the surface ocean was oxygen-rich, the deep ocean was ferruginous - oxygen-deprived and iron-dominated.

Further, sandwiched in this deep ocean was a dynamic wedge of sulfidic water, highly toxic to animal life, that impinged against the continental shelf.

Dominated by dissolved hydrogen sulfide, the sulfidic wedge was in a state of flux, varying in size and capable of encroaching on previously oxygenated areas of the continental shelf - killing all animal life there.

The overall picture is a marine basin with co-existing oxygen-rich, sulfidic and ferruginous water layers.

In the modern sulfur-rich ocean, hydrogen sulfide in oxygen-poor waters reacts with iron to form the mineral pyrite, thus stripping the dissolved iron from the water column.

But, the researchers' results show that under specific geochemical conditions in the early ocean, when levels of dissolved sulfate (the source of hydrogen sulfide in the ocean) and oxygen were particularly low compared to the modern ocean, layers of sulfidic waters could coexist with ferruginous water masses, and even persist for long periods of time.

"This is an entirely new interpretation of ancient ocean chemistry," said Chao Li, a research specialist in UC Riverside's Department of Earth Sciences and the first/lead author of the research paper.

"Our model provides a brand-new backdrop for the earliest evolution of animal life on the planet. We show that the sulfidic ocean wedge, along with an absence of oxygen, can hinder the colonization of early animals on the shallow seafloor and influence their evolution as they take a foothold," he said. (ANI)