New research reveals ocean conditions as life evolved
Geologist contributes to groundbreaking study

New research to be published the week of March 4, 2004, in Science is shedding more light on theories of evolution and the conditions of the earth as primitive life evolved. According to a team of scientists, including Timothy Lyons, associate professor of Geological Sciences, the deep oceans probably remained anoxic, or free of oxygen, for more than a billion years after the atmosphere first began accumulating oxygen 2.3 billion years ago. Such conditions would have severely restricted the portions of the ocean where diverse forms of life could have thrived and evolved.

By comparing sediments from roughly 1.5 billion years ago, during the Proterozoic Eon, with mud from the modern seafloor, the researchers concluded that the ocean probably contained less oxygen and more hydrogen sulfide than it does today. These conditions would have been more like the Black Sea where, unlike most of the modern ocean, oxygen completely disappears a few hundred feet below the sea surface. Lyons said the study is the first to test the global distributions of these prehistoric conditions.

"It is essential to understand the environmental conditions under which life evolved if we ever hope to fully grasp the relationship between nature and the early patterns and tempos of biological change," Lyons said.

In the study, the team members cite evidence gathered by comparing samples from the Black Sea and Cariaco Basin, Venezuela, to samples of mid-Proterozoic black shale from northern Australia. The team compared the molybdenum composition of the ancient muds to those from the modern sites. Molybdenum, which is a common dissolved metal in oxygen-containing seawater, plays a critical role in biological activity within the ocean.

"In the ocean, molybdenum atoms with slightly different masses, known as isotopes, behave differently from one another," Lyons said. "Understanding these differences through studies of the modern world has allowed us to constrain the relative amounts of oxygen in the ancient ocean."

Lyons says the ancient rocks in Australia shed light on conditions throughout the ocean and that Proterozoic seawater almost certainly contained substantially less oxygen than the modern ocean does.

"The study has a significant impact on the theories of evolution of life through the Proterozoic Eon, particularly at a time when eukaryotes took big steps in their evolutionary development," Lyons said. Eukaryotes are characterized by cells with a discrete nucleus containing genetic material and have evolved as a group to include humans and all other animals.

Details of this research [ abstract ] are available on the Science Web site, Science Express. For more information about Lyons' research in the Department of Geological Sciences, see his Web site. Other researchers contributing to the Science article include Gail Arnold and Ariel Anbar of the University of Rochester and Jane Barling of the University of British Columbia. The study is funded by grants from the National Science Foundation and NASA.

Additional links:

Department of Geological Sciences

Pacific Centre for Isotopic and Geochemical Research, University of British Columbia

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