Deep-sea rocks point to early oxygen on Earth

March 25, 2009

Red jasper cored from layers 3.46 billion years old suggests that not only did the oceans contain abundant oxygen then, but that the atmosphere was as oxygen rich as it is today, according to geologists.

This jasper or hematite-rich chert formed in ways similar to the way this rock forms around hydrothermal vents in the deep oceans today.

"Many people have assumed that the hematite in ancient rocks formed by the oxidation of siderite in the modern atmosphere," said Hiroshi Ohmoto, professor of geochemistry, Penn State. "That is why we wanted to drill deeper, below the water table and recover unweathered rocks."

The researchers drilled diagonally into the base of a hill in the Pilbara Craton in northwest Western Australia to obtain samples of jasper that could not have been exposed to the atmosphere or water. These jaspers could be dated to 3.46 billion years ago.

"Everyone agrees that this jasper is 3.46 billion years old," said Ohmoto. "If hematite were formed by the oxidation of siderite at any time, the hematite would be found on the outside of the siderite, but it is found inside," he reported in a recent issue of Nature Geoscience.

The next step was to determine if the hematite formed near the water's surface or in the depths. Iron compounds exposed to ultra violet light can form ferric hydroxide, which can sink to the bottom as tiny particles and then converted to hematite at temperatures of at least 140 degrees Fahrenheit.

"There are a number of cases around the world where hematite is formed in this way," says Ohmoto. "So just because there is hematite, there is not necessarily oxygen in the water or the atmosphere."

The key to determining if ultra violet light or oxygen formed the hematite is the crystalline structure of the hematite itself. If the precursors of hematite were formed at the surface, the crystalline structure of the rock would have formed from small particles aggregating producing large crystals with lots of empty spaces between. Using transmission electron microscopy, the researchers did not find that crystalline structure.

"We found that the hematite from this core was made of a single crystal and therefore was not hematite made by ultra violet radiation," said Ohmoto.

This could only happen if the deep ocean contained oxygen and the iron rich fluids came into contact at high temperatures. Ohmoto and his team believe that this specific layer of hematite formed when a plume of heated water, like those found today at hydrothermal vents, converted the iron compounds into hematite using oxygen dissolved in the deep ocean water.

"This explains why this hematite is only found in areas with active submarine volcanism," said Ohmoto. "It also means that there was oxygen in the atmosphere 3.46 billion years ago, because the only mechanism for oxygen to exist in the deep oceans is for there to be oxygen in the atmosphere."

In fact, the researchers suggest that to have sufficient oxygen at depth, there had to be as much oxygen in the atmosphere 3.46 billion years ago as there is in today's atmosphere. To have this amount of oxygen, the Earth must have had oxygen producing organisms like cyanobacteria actively producing it, placing these organisms much earlier in Earth's history than previously thought.

"Usually, we look at the remnant of what we think is biological activity to understand the Earth's biology," said Ohmoto. "Our approach is unique because we look at the mineral ferric oxide to decipher biological activity."

Ohmoto suggests that this approach eliminates the problems trying to decide if carbon residues found in sediments were biologically created or simply chemical artifacts.

Penn State

---

---

	Hematite (The Sacred Stones Series) Sometimes dreams can be enlightening but for Jessica they are a constant torment, for she grieves the loss of her father. Her stepmother has shipped her off to Blakesby, a boarding school for the elite, where Jessica’s only friend is her peppy roommate Karrie. Mid-Semester mysterious cousins Daniel and Sebastian arrive shaking up Jessica’s moody existence. Daniel is smart, sexy, and absolutely infuriating; while Sebastian is fun and flirtatious. But Jessica has no time to dwell on why these two have transferred to her school and seem to seek out her friendship…she’s got a much bigger problem. Karrie has disappeared. Now Jessica must enlist Daniel and Sebastian’s help and go on a journey that will ultimately uncover the secrets of her own past; throwing her into a world...
	Canted Antiferromagnetism: Hematite by Allan H. Morrish (Author) Hematite, the stable oxide of iron, is a major constituent of soils, rocks and the earth's crust. It has unique magnetic properties that make it the prototype for the class of materials known as canted antiferromagnets. The mean-field theory is treated in detail and information obtained by a wide variety of experimental methods is provided. These techniques include x-ray and neutron diffraction; electron magnetic resonance; Mossbauer spectroscopy; and thermal, optical, electrical and elastic measurements.
	The Brown Hematite Deposits of the Siluro-Cambrian Limestones of Lehigh County, Lying Between Shimersville, Millerstown, Schnecksville, Ballietsville, and the Lehigh River, by Frederick Prime (Author)
	Hematite: Webster's Timeline History, 1844 - 2007 by Icon Group International (Author) Webster's bibliographic and event-based timelines are comprehensive in scope, covering virtually all topics, geographic locations and people. They do so from a linguistic point of view, and in the case of this book, the focus is on "Hematite," including when used in literature (e.g. all authors that might have Hematite in their name). As such, this book represents the largest compilation of timeline events associated with Hematite when it is used in proper noun form. Webster's timelines cover bibliographic citations, patented inventions, as well as non-conventional and alternative meanings which capture ambiguities in usage. These furthermore cover all parts of speech (possessive, institutional usage, geographic usage) and contexts, including pop culture, the arts, social sciences...
	Flotation of northeast Birmingham, Ala., hematite ores by R. E. Perry (Author)
	Experimental conversion of hematite to magnetite with solid reductants by Paul A. Wasson (Author)
	Kinetics of CO reduction of hematite to magnetite and the effect of silica by John C. Nigro (Author)
	Hematite implements of the United States, together with chemical analysis of various hevatites by Warren K. Moorehead (Author) This book is a replica, produced from digital images of the original. It was scanned at the University of Toronto Libraries and may contain defects, missing pages or blemishes due to the original source content. The UT libraries have worked with various digital partners to provide the best possible customer experience and hope you enjoy the results.
	Geology and Hematite Deposits of South Cumbria (Geological Survey of Great Britain Memorial) by Geological Sciences Inst. (Author)
	Concentration experiments with the siliceous red hematite of the Birmingham district, Alabama, ([U. S.] Bureau of Mines. Bulletin 110) by Joseph T Singewald (Author)