The Impact of Tectonic Collisions on Seawater Chemistry and Climate

First published 2023

The Earth’s oceans have always been a cornerstone in shaping our planet’s climate, with their chemistry undergoing periods of stability, punctuated by brief yet transformative shifts. This link between seawater chemistry and climatic changes has profound implications for both the evolution of life and long-term atmospheric conditions. Recent studies, exploring the past 130 million years, have illuminated this deep connection, suggesting mechanisms that have been at play for over half a billion years. Geoscientists Ulrich Wortmann of the University of Toronto and Adina Paytan of the University of California Santa Cruz have been at the forefront of this groundbreaking research, emphasising the importance of seawater chemistry in understanding climatic shifts.

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The collision between the Indian subcontinent and Eurasia, occurring roughly 50 million years ago, stands as a testament to the profound effects geological events can have on our planet’s chemistry and climate. This cataclysmic encounter led to the dissolution of an extensive belt of water-soluble gypsum, which once stretched across regions from Oman to Pakistan and penetrated the heart of western India. Geologists and earth enthusiasts today can witness the echoes of this monumental event in the rugged and imposing Zagros Mountains of western Iran, which serve as a living relic of this tectonic shift.

But the implications of this event extended far beyond the terrain. The dissolution and subsequent formation of such vast gypsum reserves had a direct bearing on the oceans’ sulphate content. An alteration in these sulphate concentrations can bring about significant changes in marine ecosystems, possibly affecting biodiversity and food chains. Moreover, the sulphate content also plays a pivotal role in shaping atmospheric conditions. As the sulphate levels in the oceans vary, so does the number of sulphate aerosols in the atmosphere. These aerosols are not mere particles floating in the air; they are key actors in the Earth’s climate system, influencing temperature patterns and precipitation, thus highlighting the link between geology, ocean chemistry, and climate.

Wortmann and Paytan’s groundbreaking collaboration has brought to light a compelling hypothesis grounded in years of research and analysis. Drawing from data spanning the past 130 million years, they propose that shifts in the sulphate concentrations in the oceans act as markers for climatic change. Elevated sulphate levels, they contend, are closely associated with global cooling phases. Conversely, diminished sulphate levels often align with warmer, more greenhouse-like conditions. Central to their theory is the dissolution of vast ancient salt deposits, exemplified by the significant geological event of the India-Eurasia collision approximately 50 million years ago. This tectonic event led to the dissolution of an expansive belt of water-soluble gypsum, which had spanned regions from Oman to Pakistan and reached deep into western India. Their findings suggest that such major shifts in seawater chemistry, as observed following this collision, could have played a pivotal role in ending the Eocene epoch—a period recognised as one of the warmest in the Cenozoic era. As a result of these chemical changes, the planet began a monumental transition from a greenhouse-dominated climate to a much cooler icehouse climate, a transformation that was dramatically marked by the swift and expansive growth of the Antarctic ice sheet.

Building upon prior research, Wortmann’s insights into marine sulphate concentrations and biogeochemical cycling, paired with Paytan’s data on past seawater sulphur compositions, have enriched our understanding of the interplay between ocean chemistry and climate. These findings challenge traditional views, particularly surrounding the impact of gypsum deposits on seawater chemistry, and represent a paradigm shift in our understanding of ocean chemistry’s temporal fluctuations and their broader implications for the climate. As we move forward, acknowledging the oceans’ central role in global climate patterns becomes paramount. Protecting these vast bodies of water is not only an ecological imperative but also vital in ensuring they continue regulating our planet’s climate for the millennia to come.

Links

https://www.science.org/doi/10.1126/science.1220656

https://oceanservice.noaa.gov/facts/ocean_weather.html

https://oceanexplorer.noaa.gov/facts/climate.html

https://pubs.acs.org/doi/10.1021/acs.chemrev.5b00226

Electronegativity and Chemical Hardness Under Pressure

First published 2022

The fascinating field of high-pressure chemistry presents numerous anomalies, a majority of which have remained inexplicable within the classical understanding of chemical principles. A breakthrough research, led by a Skoltech professor and his Chinese colleagues, has however revised a foundational chemical concept – electronegativity, shedding light on the bizarre world of high-pressure chemical reactions.

Electronegativity, in simple terms, describes an atom’s tendency to either yield or capture electrons during chemical reactions. Its importance is illustrated by comparing elements with extreme electronegativities, like fluorine and cesium. These elements are so reactive that they never exist in pure form in nature. Under standard conditions, the value of an element’s electronegativity offers insights into its reactivity and the nature of bonds it can form.

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However, when one ventures beyond standard conditions, particularly under high pressures, peculiarities in chemical behaviours begin to emerge. Traditional understanding tells us that most substances on Earth exist under atmospheric pressures. Yet, the reality is that a vast majority of the Earth’s matter, and indeed that of other planets, exist under staggering pressures, with values soaring up to nearly 4 million atmospheres at the Earth’s centre. Advanced techniques, such as diamond anvil cells and predictive computational methods like USPEX, have enabled scientists to replicate and study these extreme conditions.

The revelations under these high pressures are nothing short of astonishing. Substances universally adopt metallic forms, noble gases, previously thought to be inert, form compounds, and even elements like helium engage in compound formation. The very structural periodicity of elements is disrupted, with substances like potassium adopting irregular structures. The creation of electrides, substances where electrons are relegated to lattice voids, endows the crystal with unique properties. The formation of unconventional compounds like Na3Cl, NaCl7, and high-temperature superconductors like H3S, LaH10, and YH6 further accentuate the peculiarities.

The team’s revolutionary insight came from recognising that the traditional 1934 definition of electronegativity, proposed by Robert Mulliken, was insufficient under high pressures. To bridge this gap, the team embarked on a seven-year journey of exacting calculations, redefining electronegativity in terms of its applicability under extreme pressures. Their efforts bore fruit, producing a revamped electronegativity scale that successfully accounts for these anomalous behaviors.

As pressure increases, chemical hardness, which is related to electronegativity, tends to decrease, suggesting a narrowing of bandgaps and driving elements towards a metallic state. Concurrently, electronegativity values also generally decrease, indicating that atoms become more inclined to part with their electrons. This enhanced eagerness to release electrons underpins the formation of electrides. The impact of these changes is vast, resulting in bizarre nonperiodic structures in elements like calcium, barium, and sodium.

The refined electronegativity scale also offers revelations about specific elements. For instance, under immense pressures, sodium surpasses cesium in terms of electropositivity, an anomaly given their positions on the periodic table. Additionally, elements like nickel, palladium, and platinum undergo internal electron rearrangements, rendering them more inert.

The study’s findings have profound implications that reach well beyond the confines of laboratory research or theoretical musings. The stark difference in electronegativity between elements, exemplified by the likes of magnesium and iron under immense pressure, hints at the possibility of unexpected interactions. Under regular atmospheric conditions, these elements would typically exhibit no reaction propensity towards each other, steadfastly retaining their individual properties. However, when subjected to intense pressures reminiscent of those found deep within Earth’s mantle or the cores of other celestial bodies, their chemical behaviour could drastically transform. For instance, in such high-pressure environments, elements like copper might readily interact with boron, despite being non-reactive under typical conditions. Understanding these unexpected chemical behaviors can revolutionise our knowledge of geochemical processes. It sheds light on the mysteries of mineral formations, element distribution, and even tectonic movements that transpire in the hidden depths of planets, thereby enriching the fields of geology, planetology, and beyond.

In essence, by revisiting and revising the foundational concepts of electronegativity and chemical hardness, the study has provided a comprehensive theoretical framework to decode the enigmatic world of high-pressure chemistry. The implications of this research are profound, reshaping our understanding in fields like geology, planetology, and other allied sciences.

Links

https://www.pnas.org/doi/full/10.1073/pnas.2117416119

https://www.nature.com/articles/nchem.1497

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4712861/

https://www.academia.edu/29824899/How_do_chemical_properties_of_the_atoms_change_under_pressure

https://www.nature.com/articles/s41570-020-0213-0

Chemistry Beyond Earth: Cosmic Ice and Its Implications for Life

First published 2022; revised 2023

The vast expanse of our universe presents intriguing mysteries that push the boundaries of our Earthly experiences. One of the most compelling phenomena that challenge our conventional understanding is the chemistry of cosmic ice. This unique form of ice, as revealed by research at NASA’s Goddard Space Flight Center and supported by extensive literature, provides profound insights into the fundamental differences between the chemistry we observe on Earth and that which unfolds in the cosmos.

At the heart of this contrast is the distinctive environment in which these chemical reactions take place. Earthly chemistry operates within familiar parameters of temperature, pressure, and atmospheric conditions. Conversely, the extreme conditions of space are characterised by intense cold, potent radiation, and near-vacuum environments. Such extremities lead to reactions primarily involving gases or solids, given the general absence of liquids in the vast interstellar void.

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The mystery of cosmic ice, however, goes beyond these environmental differences. Research led by Perry Gerakines at NASA’s Goddard Space Flight Center’s Cosmic Ice Lab replicates the conditions of outer space to study the exotic amorphous ice. This unique state of water is unlike the familiar crystalline structure found on Earth. Instead, amorphous ice, being disorderly and erratic, is formed under intense cold and low pressures. This deviation in the structure of something as fundamental as ice underscores the contrasting chemistries of space and our home planet.

But the significance of cosmic ice isn’t limited to its intriguing structure. It serves as a cornerstone for a widely accepted hypothesis about the origins of life on Earth. Many scholars propose that vital molecular precursors to life were formed in space, either within the dense interstellar medium (ISM) or later in the Solar Nebula. These molecules, shaped and transformed by their journey through low-temperature ices exposed to various ionizing radiations, were eventually delivered to Earth through celestial events. This interstellar voyage of molecules, coupled with the chemistry of cosmic ice, may have played a critical role in seeding life on our planet.

Deep space, far from being a desolate expanse, teems with complex organic molecules. Astronomers have identified intricate molecules, such as ethylene glycol, in the gas phase of the ISM and even within comets in our Solar System. While observing such vast molecules is fraught with challenges due to overlapping rotational lines in the spectra, our endeavours to find prebiotic molecules have been fruitful. The discovery of amino acids in meteorites like Murchison and in cometary dust particles from Comet 81P/Wild 2 provides tantalising evidence of the potential life-precursors that dance through the cosmos.

Astrochemical studies offer a fascinating window into the survivability of organic molecules in cosmic conditions, especially amino acids. The quantified “half-life doses” of specific amino acids, such as glycine, alanine, and phenylalanine, reveal how long these molecules can endure in extraterrestrial radiation environments. In dense ISM regions, for instance, amino acids are likely to have half-lives of around 107 years, aligning with the expected life cycle of an interstellar cloud core before it collapses into a protostar. The diffuse ISM, with its heightened cosmic-ray fluxes, can considerably reduce these half-lives.

The longevity of these amino acids is not just contingent on the region of space but also on the depth within extraterrestrial bodies. On Oort-cloud comets, the amino acids near the surface have a half-life ranging from 106 to 108 years. Pluto’s subsurface conditions suggest even more extended amino acid half-lives, ranging from 1–4 × 108 years. On the other hand, Europa, one of Jupiter’s moons, presents a starkly different picture. Its radiation-rich environment implies that amino acids on its surface might last only a few years. As we delve deeper into Europa, below 1 metre, the half-lives extend to potentially 6–10 million years. Mars offers yet another contrast with surface amino acid half-lives of about 108 years due to proton bombardment.

The implications of these findings are profound. The presence of amino acids in meteoritic and cometary samples suggests that they have been effectively shielded from cosmic radiation, perhaps by H2O ice or other substances. It’s tantalising to consider that if these amino acids were formed in the dense ISM, they could endure the collapse of a dense cloud core into a protostar and integrate into the primordial materials forming comets or planetesimals. Within our Solar System’s icy realms, many amino acids could survive for tens to hundreds of millions of years, provided they are embedded a few centimeters deep. It raises the prospect of detecting recently formed molecules at such depths in future exploration missions.

Moreover, the observed infrared spectra of amino acids deposited at low temperatures (15 K) reveal an intriguing conversion behaviour. The shift from the non-zwitterion to the zwitterion upon heating suggests that extraterrestrial amino acids might predominantly exist in the zwitterionic form if their icy environments ever experience temperatures of 140 K or higher. It’s essential for experimental designs studying the half-lives of these amino acids in cosmic settings to account for this transformation. The protective effect of H2O-ice on amino acids further emphasises the significance of understanding the interplay between organic molecules and their surrounding environments. Amino acids seem to thrive best within specific depth thresholds in icy celestial bodies, offering a tantalising hint at where we might focus our explorative endeavors in the quest to understand life’s cosmic origins.

In piecing together these findings, we begin to appreciate the profound implications of the chemistry of cosmic ice. Not only does it serve as a testament to the vast differences between Earthly and cosmic chemistries, but it also reshapes our understanding of the origins of life and the boundless potential of the universe. As we continue to delve into these cosmic mysteries, they not only intrigue and challenge our current knowledge but also inspire awe at the intricate dance of molecules across the vast canvas of space.

Links

https://www.sciencedirect.com/science/article/pii/S0019103512002187

https://www.mpiwg-berlin.mpg.de/research/projects/DeptIII-ChristinaWessely-Welteislehre