The 'Canfield Ocean' Guy

You've made it when you have an ocean named after you or you have a wikipedia page (albeit a short one). The "Canfield Ocean", a sulfidic, partially oxic ocean existing for more than 40% of Earth history, between the Archean and Ediacaran periods, takes its name from his seminal paper (Nature, 1998). This finding has profound implications for biological evolution, and the history of atmospheric oxygen, carbonate sedimentology and climate. Canfield and his co-workers found convincing evidence that a prolonged, stable, oxygen-rich environment following the demise of the Canfield Ocean permitted the emergence of animals capable of movement some 550 million years ago. In Dons own words
"Fossil evidence suggests that animals probably evolved sometime around 600 million years ago, and large animals appear around 575 million years ago. Animals have an absolute requirement for oxygen for their respiration, so it has often been speculated that large macroscopic animals (those with the largest oxygen requirement) evolved when oxygen rose to permissible levels, which would be about 10% of those levels we have today. Our study supports this scenario by showing that the first occurrence of large respiring organisms, some of which are likely stem-group animals, emerged on the Avalon Peninsula in Newfoundland in concordance with oxygenation of this local environment."

On Friday Don will be talking about Oxygen Minimum Zones. The Oxygen minimum zone (OMZ), is the zone in which oxygen saturation in seawater in the ocean is at its lowest. This zone occurs at depths of about 200 to 1,000 metres, depending on location. Surface ocean waters generally have O2 concentrations in equilibrium with the atmosphere. Colder waters can hold more oxygen than warmer waters. As this water sinks from the surface into deeper waters it is exposed to a rain of organic matter from above. As aerobic bacteria feed on this organic matter they use oxygen as part of the bacterial metabolic process lowering its concentration within the surrounding water. Therefore, the concentration of oxygen in deep water is dependent on the amount of oxygen it had when it was at the surface minus depletion by the degradation of organic matter. The OMZ relates to new ways scientists are looking at the 'Great Oxygenation Event'.

The reading this week is another scientific paper which puts forward the idea the delivery of nutrients to the ocean following the last of the Snowball Earth Ice Ages (the Gaskiers glaciation) feed an algal (cyanobacterial) bloom that provided enough oxygen to fuel multicellular life - in other words animals. Don and his co-authors come up with this idea because the geochemistry of sediments before the Gaskiers glaciation is different from the geochemistry of the sediments afterwards.

Video primer about oxygen and photosynthesis

The Extinction happened on Tuesday at 9:15am

Sam Bowring is a professor at MIT who specializes in Uranium-lead zircon geochronology and has gotten really good at it. The precision that he is getting on his dates are amazing. Basically zircon is a mineral (ZrSiO4) that accepts element such as U which has a large ionic radius into its structure, but rejects Pb (lead). Zircon has an almost ubiquitous presence in the crust of Earth. It occurs in igneous rocks (as primary crystallization products), in metamorphic rocks and in sedimentary rocks (as detrital grains). U-Pb dating provides an age range of about 1 million years to over 4.5 billion years, and with routine precisions in the 0.1-1 percent range. The method relies on two separate decay chains, the uranium series from ²³⁸U to ²⁰⁶Pb, with a half-life of 4.47 billion years and the actinium series from ²³⁵U to ²⁰⁷Pb, with a half-life of 704 million years. Sam will be talking about two major extinctions that occurred on Earth.

Permo-Triassic Extinctions

A major extinction event occurred approximately 250 million years ago and marks the boundary between the Permian Period and the Triassic Period. At the end of the Permian more than 85% of all species in the oceans, approximately 70% of land vertebrates, and significant numbers of plants and insects vanished. The Permian extinction caused the most fundamental reorganization of ecosystems and animal diversity in the past 500 million years. The marine communities of today are largely a result of the recovery following this extinction. In addition, dinosaurs and mammals arose in the aftermath of the extinction.

A better understanding of how long the end-Permian extinction and its recovery took will allow for new insights and better understanding into the role of mass extinctions in evolution. Mass extinctions are marked in the fossil record by the abrupt disappearance of taxa, sometimes associated with a discrete "boundary bed"; in the case of the end Cretaceous extinction this bed is a layer rich in impact ejecta with distinctive chemical signatures. A critical question is how abrupt such extinctions really were. A satisfactory answer must involve statistical analysis of the stratigraphic and fossil record. Differences in sediment accumulation rate and the preservation potential of organisms can lead to an artificially abrupt and/or drawn out extinction signal, especially if the extinction is of short duration, say, less than 1 million years. Because sedimentation rates vary, stratigraphic thickness does not convert to time directly. Therefore, understanding an extinction requires constraining its tempo by combining high-precision geochronology with paleontological studies. Sam has found that the carbon isotope event associated with the major shift in carbon reservoirs as organisms disappeared from the planet was 165 thousand years long which indicates that there was a catastrophic addition of 12-carbon into the earths system. Furthermore he has found that most of the extinctions occurred in less than 1 milion years.

P-T Video featuring Sam Bowring

monkey, monkey, where for art thou monkey

Iyad Zalmout was born in Syria. He developed a love for geology growing up in the mountains collecting fossil gastropods and bivalves to show his friends - this later morphed into collecting lizards and snakes to scare his class mates. Iyad completed his PhD at the University of Michgan with Phil Gingrich on "Late Eocene sea cows (Mammalia, Sirenia) from Wadi al Hitan in the Fayum Basin, Egypt" and has stayed as a Post-doc in the Exhibit Museum.

A year ago Iyad was looking for whale fossils in a presumed to be section of marine sediments when he began to discover terrestrial mammal fossils. He was amazed to discover what is problably the last common ancestor of apes and monkeys before the two lineages separated. With a major discovery like this, press releases were made both by the publishing journal Nature and the University of Michigan. The reading this week will be the paper published in Nature.

Slide show of the primate fossils
Nature Video

Hydrothermal activity blasts out sediment

Ted Moore is an Emeritus Professor in the Department of Geological Sciences at the University of Michigan. This position is given to a professor who has retired but is highly regarded by the department. With this title Ted has some office and research space which allows him to continue research, which he has very actively. Since he retired he has sailed on research cruises, completed lecture tours and written papers. Ted was a pioneer in the field of paleoceanography and was integral to a massive community-based research initiative called CLIMAP, whose purpose was to map out the temperatures on the planet during the last ice age, 21 thousand years ago. Ted has a speciality in micropaleontology looking a a zooplankton group known as radiolaria. Radiolaria are a amoeboid protozoa that produce intricate skeletons made of silica.

Image of radiolaria from Nest Labs at the University of Dayton.

Ted will be talking about the sediments that are deposited in the equatorial region and their interaction with hydrothermal fluid. The classic hydrothermal vent in the ocean is associated with volcanism at mid ocean ridges (sea floor spreading centers at divergent boundaries). However a recent estimate (Bekins et al. 2007 - in resources) suggests that hydrothermal fluids exiting outcrops (cliffs) of basement (meaning the rock underlying sediment) sea floor (basalt generated at mid ocean ridges) may account for 75% of the hydrothermal outflow in the equatorial Pacific. These environments have become the focus of interest by scientist interested in microrganisms - these environments maybe similar to those found on other planets and the work these microrganisms do might be very important to the formation of mineral deposits.

Cartoons illustrating the development of pits over a bedrock outcrop. (a-c) show where flanking basins have approximately the same thickness of fill and (d-f) show where the basin fill is asymmetrical.

Ted came up with the model by which pits form in deep sea sediments allowing the discharge of waters circulating through the ocean crust. This water is able to remove heat from the cooling newly formed ocean plate explaining the low heat of the equatorial Pacific plates. The model suggests that the sediments overlaying the bedrock outcrop are dissolved by the water being discharged leaving behind sediment pits. These hydrothermal discharges may also be involved in the diagenetic alteration of siliceous sediments such as those which form from the remains of radiolaria. At high temperatures the silica remains of organisms convert to porcelanite and chert as the crystal structure of the opaline or biogenic silica changes.

Chert or jasper in the jasper conglomerate outside the CC Little building

Bedrock rivers and active deformation

Brian Yanites is a Post-doctoral Researcher in the Department of Geological Sciences at the University of Michigan. Brian did his PhD in Boulder at the University of Colorado with Greg Tucker.

Brian is interested in geomorphology - geologic research tries to understand the origin of the landforms (mountains, rivers etc) on Earth. On his web page he says he is trying to answer two fundamental questions: 1) How do local processes interact to form landforms and landscapes? and 2) How can we, as researchers, appropriately model and constrain these processes to explore the long-term evolution of the earth’s surface?

On Friday Brian will be talking about how to use river incision to understand deformation. Let's break that down. River incision refers to a river eroding downward through its riverbed which may be made of sediment or bedrock.The river begins at a higher elevation and incises or cuts or erodes downward through the bed it flows over. The river may leave its floodplain behind at a higher elevation of it may be lowered at the same time. Deformation refers to changes in the shape or volume of a rock body. Stress/pressure is often applied to rock bodies by plate tectonics for example. Rock bodies may bend in a ductile fashion (forming anticlines or synclines) or in a brittle fashion (faults that fracture rock bodies).

Rail lines outside Christchurch, New Zealand deformed in a ductile fashion in response of the earthquake of September 3rd 2010 (photo by Ian McGregor).

As the rock body under a river deforms, the river bed responds by becoming steeper (the elevation change down the river bed increases) and the width of the river bed becomes narrower (less distance between either side of the river bank). Both responses cause the river to become more erosive and the river will incise or cut down through its river bed faster. If the age of the beginning of the incision/cutting down is known, then the geomorphologist can calculate how quickly the river is eroding its bedrock.

Brian will be talking about rivers that drain off the Tibetan plateau. He has calculated how fast the rivers are incising the landscape by dating the time when incision began. Brian has used known earthquakes events as well as optically stimulated luminescence (OSL) dating techniques to calculate when the river sediments last saw sunlight to date the beginning of incision. Using his results Brian has helped us further understand the tectonics that are actively shaping our planet.

You can read more about these techniques at 'Rivers crossing growing folds' or in the Yanites folder in resources on Ctools.

Introductions: September 10 2010

New faculty, postdoctral researchers and graduate students will be introduced in this weeks Smith Lecture. There will be no lecture discussion as a result.