Publications


Quantitative discrimination between geological materials with variable density contrast by high resolution X-ray computed tomography: An example using amygdule size-distribution in ancient lava flows

by

Som, S.M., Hagadorn, J.W., Thelen, W.A., Gillespie, A.R., Catling, D.C. & Buick, R.

Computers & Geosciences, 54, pp 231-238.

doi:10.1016/j.cageo.2012.11.019, 2013.

Brief summary

In this methods paper, we present a new way to measure geological objects (such as air pockets, mineral-filled air pockets, crystals, and fractures) trapped within geological materials (such as volcanic rocks, other volcanic debris, and construction cement). Such objects are typically of different densities compared to the material they are trapped inside of. This allows the use of X-rays to identify them (akin to dentists using X-ray to get a closer look at a patient’s teeth). Coupled with X-ray detection, we present new software-based techniques that we have developed to extract these objects from the raw X-ray images in order to obtain quantitative information about them, such as their volume distribution and associated statistics. This type of information is important because they can tell a story about what happened to those rocks.

Extended summary

The size and size distributions of geological objects trapped in geological materials can be useful to scientists and civil engineers because they can reveal the history of the rocks, provide constraints on the environmental conditions that prevailed while they were formed, and reveal physical processes that have acted on them since formation.

Measuring such trapped objects is challenging because physically accessing them can cause their destruction as rocks are very brittle. While different techniques do exist, X-ray tomography has proved to be the most effective method, particularly when there is a strong contrast between the material and the object (for example: a fracture in cement, or an air bubble in a volcanic rock). The use of X-rays to measure objects with variable densities (such as voids filled in with several minerals, each with a different density) has not been significantly studied.

Gas bubbles identified inside a 4cm tall rock core using the method described in this paper.

The result of X-ray scans are gray scale images, where “black” represents very low density and “white” represents very high density. Voids and fractures appear black, while rock and cement are gray. When working with voids, it is easy to tell a software to identify “black” as the object of interest while ignoring the rest. This method becomes impossible to apply when the objects of interest are also gray (but of varying different shades of gray from the parent material). To enable such studies, we have developed new software-based techniques to isolate such variable density objects from the parent material. The method relies on the grayscale gradient, rather than its absolute value. To illustrate the method, we have implemented it as a proof-of-concept on 2.7 billion year old lava flows, where the air bubbles have been filled-in by subsequent mineralization.

We also present mathematical techniques to obtain the mean size of those objects in a way that allows statements to be made about the statistics of the entire rock unit, rather than the sample alone. This involves bootstrap mathematics and application of the Central Limit Theorem.

Cosmic rays and terrestrial life: A brief review

by

Atri, D. & Melott, A.

Astroparticle Physics, in press.

doi:10.1016/j.astropartphys.2013.03.001, 2013.

[arXiv] [Materia]

Listen to the author interview! [mp3 download]

Brief summary

Our Galaxy is filled with high-energy subatomic particles generated by exploding stars or supernovae, also known as cosmic rays. These particles strike the Earth’s atmosphere and produce more particles, which damages the ozone layer and causes DNA damage to terrestrial and marine life. We have presented a brief account of both periodic and non-periodic sources of cosmic ray variations over long timescales and their effects on terrestrial life.

[Discussion on S.A.G.A.N.]

Extended summary

High-energy radiation bursts are commonplace in our Universe. From nearby solar flares to distant gamma ray bursts, a variety of physical processes accelerate charged particles to a wide range of energies, which subsequently reach the Earth. Such particles contribute to a number of physical processes occurring in the Earth system. A large fraction of the energy of charged particles gets deposited in the atmosphere, ionizing the atmosphere, causing changes in its chemistry and affecting the global electric circuit. Remaining secondary particles contribute to the background dose of cosmic rays on the surface and parts of the subsurface region.

Life has evolved over the past ~ 3 billion years in presence of this background radiation, which itself has varied considerably during the period. As demonstrated by the Miller-Urey experiment, lightning plays a very important role in the formation of complex organic molecules, which are the building blocks of more complex structures forming life. There is growing evidence of increase in the lightning rate with increasing flux of charged particles. Is there a connection between enhanced rate of cosmic rays and the origin of life? Cosmic ray secondaries are also known to damage DNA and cause mutations, leading to cancer and other diseases. It is now possible to compute radiation doses from secondary particles, in particular muons and neutrons. Have the variations in cosmic ray flux affected the evolution of life on earth? We describe the mechanisms of cosmic rays affecting terrestrial life and review the potential implications of the variation of high-energy astrophysical radiation on the history of life on earth.

Double catastrophe: Intermittent stratospheric geoengineering induced by societal collapse

by

Baum, S.D., Maher, T.M., Jr. & Haqq-Misra, J.

Environment Systems & Decisions, 33, pp 168-180.

doi:10.1007/s10669-012-9429-y, 2013.

[Scientific American] [Overcoming Bias] [National Geographic] [Geoengineering Watch]

Listen to the author interview! [mp3 download]

Brief summary

If geoengineering by injection of aerosol particles into the stratosphere is deployed, then the occurrence of a global catastrophe could cause intermittency in geoengineering and lead to total damages far greater than if either situation occurred in isolation. While the outcomes of the double catastrophe are difficult to predict, plausible worst-case scenarios include human extinction. This double catastrophe scenario strengthens arguments for greenhouse gas emissions reductions and demonstrates the value of integrative, systems-based global catastrophic risk analysis.

Extended summary

Background: Global Catastrophic Risk Systems Analysis – Global catastrophic risks are risks of events that would significantly harm or even destroy humanity at the global scale, such as climate change, nuclear war, and pandemics. To date, most research on global catastrophes analyzes one risk at a time. A better approach uses systems analysis to capture the many important interactions between risks. This paper analyzes a global catastrophe scenario involving climate change, geoengineering, and another catastrophe. We call the scenario “double catastrophe”.

Climate Change & Stratospheric Geoengineering – The rising temperatures of global climate change pose great risks to humanity and ecosystems. Climate change can be slowed by reducing emissions of greenhouse gases like carbon dioxide and methane. But humanity has been struggling to reduce emissions. One alternative is geoengineering, the intentional manipulation of Earth systems. The most promising geoengineering option may be stratospheric geoengineering, in which aerosol particles are put into the stratosphere. The particles block sunlight, lowering temperatures on Earth’s surface.

Intermittency & Double Catastrophe – One problem with stratospheric geoengineering, known as intermittency, is that the particles must be continuously replaced in the stratosphere. If they’re not, then in a few years they fall out, and temperatures rapidly rise back to where they would have been without the geoengineering. The rapid temperature increase would be very damaging to society. Because of this, society is unlikely to let intermittency occur – unless some other catastrophe occurs, knocking out society’s ability to continue the geoengineering. Then, the rapid temperature increase hits a population already vulnerable from the initial catastrophe. This double catastrophe could be a major global catastrophe.

Implications For Decision Making – Because of how damaging global catastrophes would be to human civilization, decision making is often oriented towards minimizing the risk of global catastrophe. Stratospheric geoengineering can prevent global catastrophe from climate change alone, but it can also lead to global catastrophe from the double catastrophe scenario. If global catastrophe is more likely from climate change alone, then society should decide to implement stratospheric geoengineering. Otherwise, society is better off without stratospheric geoengineering. This assumes (among other things) that the goal should be minimizing global catastrophic risk and that stratospheric geoengineering is the best form of geoengineering.

Scaling relationships and concavity of small valleys on Mars

by

Penido, J., Fassett, C. & Som, S.

Planetary and Space Science, 75, pp 105-116.

doi: 10.1016/j.pss.2012.09.009, 2012.

Brief Summary

The shape of a river can be a proxy for the climate that existed during river incision. How the river’s slope changes downstream and how the river’s width changes downstream are two of several parameters that can be used to assess whether or not a river has seen continuous water flow for geologically meaningful time. We use these parameters to investigate several valley networks (i.e. what look like dry river beds) on Mars and found that while rain was likely responsible for their formation, they do not compare well with rivers on Earth that have seen continuous water flow throughout their history.

[Discussion on S.A.G.A.N.]

Extended summary

Sediment transported by water in rivers act similar to sand paper and slowly erode into the rock, giving “mature” rivers (rivers that have flowed continuously for a long time) a shape that is characteristic to them. That shape holds true for small rivers and large ones. As long as the water has flown for a long time, the river will reach a so called “equilibrium shape”, with slope decreasing downstream in a predictable way, and width increasing downstream in a predictable way, among other parameters.

We apply such predictions to Mars, and see if the shape of the (now dry) river beds have recorded a period in Mars’ history when the planet was warm enough (and had a thick enough atmosphere) to allow for liquid water to flow for geologically meaningful time (millions of years – which is still on the shorter side, geologically speaking). Previous studies had focused on the larger dry river beds found on Mars, because of the coarseness of the data used then, that came from the Mars Orbiter Laser Altimeter (or MOLA). Here, we used stereo images (images of the same area taken from different angular perspectives) from more recent spacecraft to create 3D elevation maps and thus were able to make such measurements on much smaller dry river beds.

We find that the predictability of river shapes flowing continuously on Earth is poorly, if not at all, found to apply on Mars. There is enough quantitative resemblance to suggest that rain was likely responsible for carving those martian valleys, but that’s where the resemblance ends. It is thus plausible that the climate on early Mars never allowed for the water to flow for long enough time for the river shapes to evolve to the point of being comparable to Earth’s continuously flowing rivers. If this is true, then the entire concepts of early Mars having oceans on its surface becomes very difficult to ascertain.


An ecological compass for planetary engineering

by

Haqq-Misra, J.

Astrobiology, 12, pp 985-997.

doi:10.1089/ast.2011.0796, 2013.

Listen to the author interview! [mp3 download]

Brief summary

Planetary engineering describes any willful attempt by humans to modify a planetay system through technological means. This includes present-day proposals to counter climate change with geoengineering as well as more distant projections of terraforming the climate of Mars to make it habitable for Earth life. This paper develops a two-axis framework for environmental ethics that considers how we assign value across the spectrum of life on Earth. This tool may be useful for thinking about how human activities will affect organisms, environments, planetary systems, and space.

[Discussion on S.A.G.A.N.]

Extended summary

Only recently have humans gained the capability to willfully and technologically manipulate the environment on a global scale. This sort of planetary engineering includes present-day geoengineering proposals to counteract anthropogenic climate change by reflecting away a fraction of incoming sunlight. Although such a feat seems technically achievable, whether or not we should engage in such geoengineering is a question of ethics.

Other, more futuristic, kinds of planetary engineering include plans for terraforming Mars to increase global temperatures and make the red planet habitable for Earth life. For terraforming as well, the technology for terraforming may be available today, but whether or not we should deliberately modify another planet is a question of ethics. In this study, we develop a two-axis framework for comparing different views about how we value organisms, environments, planetary systems, and space. This ecological compass is shown in the figure with a scale from “space” to “intelligence” along the horizontal axis. This axis is intended to represent the vast diversity of life on Earth, from humans and other animals on the far right, to microscopic organisms near the middle, to planetary systems and space on the far left. The vertical axis of the ecological compass contrasts two types of value: instrumental value and intrinsic value. Instrumental value describes the usefulness or purpose that an object, organism, or system provides; for example, a logger may assign instrumental value to trees that are grown for lumber. Intrinsic value describes the an object, organism, or system as valuable for its own sake; in this sense, a hiker may view a tree as valuable simply by virtue of its being a tree. With this two-axis system, we can describe and compare various attitudes toward nature and their implications for planetary engineering.

An anthropocentric view, which assigns instrumental value to all life other than humans, may find no environmental objection to planetary engineering. This is because anthropocentrism is only concerned with the effects of planetary engineering on humans. A zoocentric (or ratiocentric) framework extends intrinsic value to animals and gives at least some consideration to how human actions affect these organisms. As such, zoocentrism suggests that some consideration should be given to the effects of geoenginering on non-human animals. Likewise, a macrocentric viewpoint considers large, visible organisms as intrinsically valuable, while a microcentric viewpoint considers even microorganisms to possess intrinsic value. Under these ethical frameworks, the decision to terraform a planet such as Mars will depend upon the organisms that are already inhabiting it. Finally, a cosmocentric framework places intrinsic value across the entire biological spectrum from intelligent creatures and microorganisms to planets and space. This suggests that a cosmocentric ethical framework would refrain from any sort of planetary engineering because a planet is valued for its own sake.

This ecological compass is intended to be used as a tool for discussions of human valuation of nature. As a tool it cannot provide the answer to whether or not we should engage in planetary engineering, but it can at least help us raise important questions about how we value nature in advance of any decisions.