Archives

Origin & Evolution of Life: May 2010


Early Oceans, Early Animals

The Ediacaran Period (635-542 million years ago) was a time of fundamental environmental and evolutionary change, culminating in the first appearance of macroscopic animals. A new study from NAI's Arizona State University Team outlines a detailed record of Ediacaran ocean chemistry for the Doushantuo Formation in the Nanhua Basin, South China. Their results suggest a stratified ocean was maintained dynamically throughout the Ediacaran Period. Their model reconciles seemingly conflicting geochemical conditions proposed previously for Ediacaran deep oceans, and helps explain the patchy fossil record of early metazoans. Their paper appears in the April 2nd issue of Science.

[Source: NAI Newsletter]

Microbial Iron Reduction in BIF's?

Studies of modern sedimentary analogs to ancient rock precursors are critical to gain insight into the biogeochemical processes responsible for generating unique chemical or isotopic compositions in ancient rocks. A recent study published by the University of Wisconsin NAI Team in Geobiology provides an example of such a modern analog study in the context of Archean and Paleoproterozoic Banded Iron Formations (BIFs). Sediments downstream of the Iron Mountain acid mine drainage site in northern California were examined for their chemical and Fe isotope composition, as well as the presence and activity of iron-reducing microorganisms. The results link dissimilatory microbial iron reduction (DIR) to the generation of large quantities of aqueous (mobile) ferrous iron, and provide the first demonstration of Fe isotope fractionation in an environment where DIR has been shown by microbiological methods to be active in sediment metabolism. These findings provide insight into pathways whereby DIR could have led to the formation of isotopically-light Fe-bearing minerals in BIFs.

[Source: NAI Newsletter]

The evolution of complex life forms may have gotten a jump start billions of years ago, when geologic events operating over millions of years caused large quantities of phosphorus to wash into the oceans. According to this model, proposed in a new paper by Dominic Papineau of NAI's Carnegie Institution of Washington team, the higher levels of phosphorus would have caused vast algal blooms, pumping extra oxygen into the environment which allowed larger, more complex types of organisms to thrive.

"Phosphate rocks formed only sporadically during geologic history," says Papineau, a researcher at Carnegie's Geophysical Laboratory, "and it is striking that their occurrences coincided with major global biogeochemical changes as well as significant leaps in biological evolution."

In his study, published in the journal Astrobiology, Papineau focused on the phosphate deposits that formed during an interval of geologic time known as the Proterozoic, from 2.5 billion years ago to about 540 million years ago. "This time period is very critical in the history of the Earth, because there are several independent lines of evidence that show that oxygen really increased during its beginning and end," says Papineau. The previous atmosphere was possibly methane-rich, which would have given the sky an orangish color. "So this is the time that the sky literally began to become blue."

For more information: http://astrobiology.nasa.gov/articles/did-phosphorous-trigger-blue-skies/

[Source: NAI Newsletter]

Date/Time: Monday, June 7, 2010 11:00AM Pacific
Speaker: Katrina Edwards (University of Southern California)
Title: "Intraterrestrial Life on Earth"

In 1986, scientists sailing in the Pacific Ocean made an astonishing discovery. In sediments collected from 850m below the seafloor, they identified that microbes were living and thriving in an environment not previously known to contain life. This discovery has spawned a new field of research on the "deep biosphere" with researchers exploring how life persists and evolves at hostile temperatures and pressures. With estimates that the sub-seafloor may contain as much two-thirds of the Earth's microbial population, research today focuses on understanding the importance, or lack thereof, of this community to the Earth's systems. This presentation will focus on the current state of knowledge with respect to the deep biosphere and the major questions being addressed in this field, such as what are the nature and extent of life on Earth? What are the physico-chemical limits of life on Earth? How metabolically active is the deep biosphere, and what are the most important redox processes? What are the dispersal mechanisms for life in the deep biosphere? How does life evolve in deeply buried geological deposits that can occur more than a km beneath the ocean floor? What is the influence of the deep biosphere on global-scale biogeochemical processes?

For more information and participation instructions: http://astrobiology.nasa.gov/nai/seminars/detail/174

[Source: NAI Newsletter]