steady-state shape for a grain due to perturbation in surface tension

Carbon Isotope Delta Notation

An Early Volcanic Trigger for Earth's Biggest Extinction

The most devastating extinction in earth history spanned the Permian-Triassic boundary, about 250 million years ago. The fossil record shows that over 90% of marine species were lost between the mid Permian and the early Triassic. However, not all species were affected equally. Immobile species, species without sophisticated respiratory systems, and species producing shells or other body parts from calcium carbonate died out in greater proportions.

Prior to the end of the Permian, fusilinids, a now-extinct calcite-shelled organism, were known to form entire limestone formations.

This pattern is consistent with hypercapnia, or elevated levels of atmospheric carbon dioxide. As carbon dioxide levels increase, the gas begins to dissolve into the ocean, increasing acidity. This makes it more difficult to produce shells made of calcium carbonate, which dissolves under acidic conditions. Additionally, species without sophisticated respiratory systems can't cope with the elevated levels of waste gas.

Elevated levels of carbon dioxide hinder the production of calcium carbonate shells.

To pinpoint the root cause or causes of the series of extinction events through the mid-Permian to early Triassic, a carbon dioxide source is needed. Volcanism can raise carbon dioxide levels; volcanos give off moderate amounts of carbon dioxide during eruption. However, volcanic heat can also burn any coal or other carbon deposits within range. This gives off significantly greater quantities of carbon dioxide and other noxious gases than volcanism alone, especially if the area heated is large. Warming resulting from higher carbon dioxide levels also decreases the solubility of oxygen in water, decreasing the amount available to marine life.

The Emeishan Traps flood basalts, which date to about 260 million years ago, were one of the largest volcanic eruptions in earth history.

It is a challenge to evaluate the timing of volcanic events relative to sedimentary deposition. However, a recent paper by Paul Wignall and colleagues ties Emeishan traps volcanism to the first pulse of the Permian-Triassic extinction. Dated to the mid-Permian, the Emeishan traps are the twelfth largest volcanic eruption in earth history. The area studied, in southern China, included fossiliferous limestones that were interbedded with volcanic rocks resulting from the eruptions. This allowed the team to observe that a number of species last appeared just below the initial phases of eruption, providing a close link between the two events. The team also found that changes in ocean chemistry recorded in the limestones were consistent with significant volcanic burning of fossil carbon, which would increase the impact of the event. While the eruption of the Emeishan traps is probably too early to explain the later phases of the Permian-Triassic extinction, its identification as an early trigger brings us closer to understanding the initial phases. This study may also provide a model for linking the later, larger eruption of the Siberian traps flood basalt to later phases of the P-T extinction.


Wignall, P.B., Sun Y-D., Bond, D.P.G., Izon, G., Newton, R.J., Védrine, S., Widdowson, M., Ali, J.R., Lai X-L., Jiang H-S., Cope, H. & Bottrell, S.H. 2009. Volcanism, mass extinction and carbon isotope fluctuations in the Middle Permian of China. Science, 324, 1179-1182.

Isotope Dilution

Note: As an example, this equation is for calculating concentration of Rb, but the basic equation can be used for any system.

ConcN = the Concentration of the sample (what you want to find out)

At. wt.N = the atomic weight of the sample (measured)

99.40/0.6 = the spike 87Rb/85Rb ratio (known)

R = measured isotope ratio (measured)

27.83/72.17 = natural 87Rb/85Rb ratio (known)

wt.s = mass of spike (measured)

wt.n = mass of sample (measured)

ConcS = concentration of spike (known)

At. wt.S = atomic weight of spike (known)

Modified radioactive decay equation

Energy Conservation Equation

Taking the Temperature of an Early Solar System Meteorite

Using textural observations and the chemistry of a chondritic meteorite, NWA-6104, that formed early in our solar system’s history, the temperatures that the meteorite experienced after formation were determined. Chondritic meteorites were created at the dawn of our solar system and, after ~4.5 billion years, still retain much of their original chemistry. Many planetary bodies that orbit our sun like Earth and Mars have undergone significant melting and differentiation (separation of core and mantle). Unlike these bodies, chondrites have not undergone significant melting or differentiation; the temperatures and pressures that chondritic meteorites have experienced simply haven’t been high enough to melt them. By studying their chemistry, conditions of the solar nebula within which they formed can be hypothesized. After their formation, chondrites were subject to differing degrees of metamorphism (solid-state alteration) by heat and fluids. Through evaluating the degree to which they were altered, conditions of planetesimals that did not undergo significant melting or differentiation can be constrained.

Artist's depiction of a solar nebula and subsequent evolution of our solar system (image taken from panoramicuniverse.com)

Chondrites contain distinct, millimeter-sized spheres called chondrules. These objects originated as free-floating molten droplets that were flash heated and later crystallized. Chondrules give chondrites the appearance of chocolate chip cookies, with chondrules representing the chocolate chips and a matrix representing the dough. For a research project, I used a petrographic microscope to characterize the textures of the chondrules within a meteorite that formed early in our solar system’s history to help determine the degree of thermal and aqueous alteration. I also used an electron microprobe, a machine that uses beams of charged particles to measure the chemistry of samples, to analyze its chemistry and classify it, as it had not been previously studied.

Photomicrograph of an olivine chondrule. Notice the round shape of a remnant chondrule in the center surrounded by matrix.

Textural observations and the chemistry of NWA-6104 classified it as an L5/6 chondrite. L stands for low iron bearing and 5/6 characterizes the degree of alteration, with 3 being the lowest possible degree. Meteorites with values above or below 3 experience either thermal or aqueous alteration, respectively. The degree of thermal alteration (5/6) was determined petrographically by certain textural criterion. Because the highest possible degree of thermal metamorphism is a rating of 6, this meteorite experienced significant thermal alteration. Chemical analyses and the use of a pyroxene-pyroxene geothermometer (a method of comparing the chemistry of two very closely related minerals, orthopyroxene and clinopyroxene) constrained the peak metamorphic temperatures that the parent body of NWA-6104 experienced to 800-900 ±50 °C. This range of temperatures is consistent with the degree of metamorphism that would be expected for a 5/6 ordinary chondrite.

To see the original paper from which this post was whittled, please go here.

Air travel disruptions following major volcanic eruptions

Following major volcanic eruptions, plumes of ash and steam raise many kilometers into the atmosphere where ash can be dispersed over a wide area. The injection of this material into the atmosphere effects the evolution of atmospheric chemistry and can influence short term weather patterns. The ash in the atmosphere also makes it unsafe for airplanes to travel through, as was the case following the eruption in Iceland last April which resulted in tens of thousands of flight cancellations.

Extent of the Plume from the Eyjafjallajökull Volcano in Iceland, from earthobservatory.nasa.gov

A volcanic plume has to be buoyant to reach 10's of km into the atmosphere. The hot gases and ashes cool as the plume rises in the atmosphere, and the plume expands. This keeps the plume less dense than the surrounding atmosphere and keeps the plume rising, in the same way bubbles rise in a glass of soda.

Sarychev Peak Eruption June 12, 2009 taken from the International Space Station, from earthobservatory.nasa.gov

Work was completed at NASA's Goddard Space Flight Center to investigate how these plumes rise. While there are numerous conditions that are looked at, the effects of vent geometry has on supporting a buoyant plume was investigated. Computer models of volcanic plumes originating from linear and circular vents were constructed. From the simulations the maximum height at which a buoyant plume can reach was determined. Simulations were done with different vent openings to see if a linear vent can produce a plume which can reach heights similar to that of plumes from circular vents.

Maximum predicted plume heights on Earth as a function of vent area. The linear vent results are shown for multiple choices of active fissure length

The results show that when buoyancy is sustained, linear vents appear to be equally capable of injecting ash and volatiles into the atmosphere. For analogous mass flux rates at the vent, the maximum heights to which linear and cylindrical plumes can rise are comparable. However, in some cases where the length of an active linear vent is smaller than the radius of the circular vent, the entrainment area of the linear plumes is significantly less than the cylindrical equivalent. Thus the range of vent widths that can sustain a buoyant plume is narrow and linear plumes are more likely to collapse and not inject ash high into the atmosphere.

For a more detailed description, please see the paper Glaze et al., 2011

Glaze, L. S., S. M. Baloga, and J. Wimert (2011), Explosive volcanic eruptions from linear vents on Earth, Venus, and Mars: Comparisons with circular vent eruptions, J. Geophys. Res., 116, E01011, doi:10.1029/2010JE003577.

Sub-zero temperature acid-weathering on Mars

In a recent study, acid-weathering in sub-zero temperatures was found to occur at rates and magnitudes comparable to those from 0 °C to at least room temperature. This type of weathering may have been an important process on Mars. Temperatures today range from about -90 to -5 °C and the sulfate-rich sediments suggest weathering via an acidic medium, possibly sulfuric acid. Further, the temperature of Mars in the past is an issue of contention because it has implications for the presence of stable liquid water on the Martian surface. Many features on Mars appear to have been created by flowing liquid water, such as gullies, outflow channels, and valley networks, but the evidence is not conclusive. Some of these features may have been formed through the periodic melting of permafrost. This leaves the fundamental question of how warm or cold was Mars? The aforementioned study was conducted in order to expand our understanding of acid-weathering to the sub-zero temperature regime and to investigate a possible low temperature source for sulfate-rich sediments on Mars that were discovered by the hugely successful Opportunity Mars Exploration Rover. The research concerning the genesis of these sediments may provide a clue to Mars’ past climate.

Mars, as seen by the Opportunity rover, in foreground. For scale, the distance between tire tacks is about 1 meter. Image is a photomosaic, courtesy NASA/JPL Photojournal.

Upon landing, Opportunity found a vast, sandy, windblown plain. This plain is essentially a large-scale deposit of sulfate-rich sediment, characterized by fine layering, cross-bedding, and hematite spherules, which are tiny spheres of an iron oxide mineral – or as they are better known, “blueberries”. Finally, a mineral called jarosite, an iron sulfate, was found in abundance. The origins of the sediment and the depositional features are debated, but a popular hypothesis suggests that they originated through alteration processes in a groundwater-fed evaporative dry lake bed. Alternatively, it has been suggested that the sediments were altered via acid-weathering in a massive dust-ice deposit and later reworked by wind. These hypotheses differ mainly in the temperature of the region. Were the sediments altered to their present state in a warmer or colder climate? To test the ice-weathering hypothesis, sub-zero temperature acid-weathering must first be understood. Reaction kinetics are necessarily slower below 0 °C. However, acid-weathering, especially the effect of temperature on acidity and the effect of acidity on weathering, below 0 °C is not as well understood as it is at >0 °C. The situation is complicated by the formation of ice. As ice forms, the remaining acidic solution becomes more and more concentrated. The acid concentration can therefore increase as temperature decreases, which may mitigate the effect of the cold.

The fine layering of the sediments can only be seen inside craters. This image was taken inside Endurance Crater. Image is a photomosaic, courtesy NASA/JPL Photojournal.

A preliminary study was conducted in order to investigate the rate of acid-weathering at very low temperatures. In this study, olivine, a magnesium- and iron-bearing silicate mineral ((Mg,Fe)₂SiO₄), was exposed to sulfuric acid under different temperature conditions (the lowest of which was -52 °C) for varying amounts of time. The resulting solution was analyzed for dissolved Mg²⁺ and Fe²⁺ ions, which would indicate weathering of the olivine. The solid residue was examined for evidence of weathering using a sophisticated microscope with imaging and qualitative chemical analysis capabilities.

Images of two olivine grains. A. is a residue grain from the longest duration -20 °C sample. B. is from the least weathered sample (-52 °C, 1 hour) for comparison, though the two samples are not related. Chemical analyses are also shown, showing differing Mg:Si between the two samples. This ratio change indicates some degree of weathering.

The results of the analyses, as stated previously, suggest that acid-weathering occurred in even the coldest temperatures. Both Mg²⁺ and Fe²⁺ were found in all the solutions, with the samples in the coldest conditions having the lowest concentrations. Additionally, the concentration of the acid seemed to compensate for the colder temperatures in the first 24 to 40 hours. However, the rate of weathering drops off very quickly in the coldest temperatures, indicating that the temperature does play a large role in slowing the reaction kinetics. Furthermore, the images and chemical analysis of the solid residue give compositional and textural evidence of sub-zero temperature acid-weathering. The ratio of Mg to Si is much lower than typical Mg-rich olivine composition in darker colored areas and spots (color differences indicate compositional differences in these images), showing that some degree of weathering has occurred. It seems, then, that the ice-weathering hypothesis is possible, but that will not end the debate of the role of liquid or ice water on Mars or its part in Mars’ past climate.

For additional information about this study and references, see the abstract.