Tag Archives: #water

How Much Water Was Delivered From The Asteroid Belt To The Earth After Its Formation? (Planetary Science)

How much water could have been brought to the Earth through asteroid collisions after the formation of earth? Rebecca Martin and Mario Livio now answered this question by using N-body simulations and by comparing the relative impact efficiencies of 3 radially narrow regions of the asteroid belts. Their study recently appeared in Arxiv.

As we all know, the planets in the inner solar system are relatively dry. The precise amount of water in and on the Earth is unknown, but is thought to be between one and ten “oceans”, where one ocean is about 2.5 × 10¯4 M or the mass of water on the Earth’s surface. The question is, how the Earth could have formed with its current amount of water, as it is not possible for Earth to form water by its own. Thus, there have been several suggestions: through adsorption of hydrogen molecules on to silicate grains, delivery of water through meteorites and icy pebbles etc. But, the current leading scenario for the majority of the water delivery is by external pollution from the outer parts of the asteroid belt.

So, by considering this, Martin and Livio now described their n-body simulations in which they modeled three radially narrow regions of the asteroid belt: the ν6 resonance (at about 2.1 au), the 2:1 mean motion resonance with Jupiter (at about 3.3 au) and the chaotic region outside of the asteroid belt. Next, they compared the relative impact
efficiencies between asteroids in these regions and the Earth.

“Our analysis assumed that the asteroid belt contained its primordial mass after the Earth had formed and the giant planets were on their current day orbits. Thus, we have skewed the assumptions to estimate an upper limit to the amount of water that could have been delivered to the Earth.”

They showed that the majority of asteroid collisions with the Earth originate from the ν6 resonance at the inner edge of the asteroid belt. About 2% of asteroids from the resonance collide with the Earth. While, the collision probability from the 2:1 mean motion resonance is about one hundred times smaller and from the chaotic region about a thousand times smaller.

(article continues below image)

Figure 1. The outcomes of the n-body simulations in time binned into 0.5 Myr intervals. Note that the points are slightly offset from the centre of the time bin so that they don’t completely overlap. The upper panels have the Earth radius of REarth = 1 R⊕ while the lower panels have Earth radius of REarth = 10 R⊕. The left panels show the simulation of the ν6 resonance in the range a = 2.0-2.1 au. The middle panels show the 2:1 resonance in the range a = 3.3 – 3.35 au. The right panels show the simulation in the region 4 – 4.1 au. The blue points show asteroids that are ejected. The red points show asteroids that hit the Sun. The green points show asteroids that hit the Earth. The magenta points show asteroids that hit Jupiter or Saturn. © Martin and Livio

They also estimated that, if the majority of asteroids in the primordial asteroid belt were moved into the ν6 resonance either through asteroid-asteroid interactions or gas drag, or the Yarkovsky effect, then at most, the asteroid belt could have delivered about eight oceans worth of water. Thus, the delivery of one ocean’s worth from the asteroid belt was certainly possible.

“However, the delivery of 10 oceans worth could have been difficult and if the Earth’s mantle contains such significant amounts of water then the Earth likely formed with a good fraction of it.”

— concluded authors of the study

Reference: Rebecca G. Martin and Mario Livio, “How much water was delivered from the asteroid belt to the Earth after its formation?”, Arxiv, pp. 1-5, 2021. https://arxiv.org/abs/2106.03999

Note for editors of other websites: To reuse this article fully or partially kindly give credit either to our author/editor S. Aman or provide a link of our article

Scientists Reveal Effects of Water on 660 km Discontinuity in the Deep Earth (Earth Science)

The seismic discontinuity that occurs at an average depth of 647-654 km, usually called the 660 km seismic discontinuity, is the boundary between the transition zone and the lower mantle. It is considered to be caused by the transformation of ringwoodite to bridgmanite and MgO (post-spinel transition).

One important parameter that can potentially affect the post-spinel transition is hydration. According to recent studies, the transition zone may contain significant amounts of water, and thus understanding the effect of water on the post-spinel transition is important to determine its properties.

Dr. Joshua Muir, the postdoctoral researcher, and the team leader Prof. ZHANG Feiwu from the Institute of Geochemistry of the Chinese Academy of Sciences (IGCAS), in collaboration with Prof. John Brodholt from University College London (UCL), investigated the effect of water on the post-spinel transition at high temperatures and pressures.

The results indicated that the water only had a very small effect on the Clapeyron slope of the post-spinel transition. On the other hand, water had a moderate effect on its depth. 1 wt.% water increased the depth of phase transition onset by about 8 km. This variation on depth was relatively small compared to seismically observed variations in the 660 km discontinuity of around 35 km and so water alone could not account for the observed 660 km discontinuity topography.

Furthermore, this study demonstrated that the addition of water caused a large broadening of the three-phase loop (ringwoodite + bridgmanite + MgO) through the development of post-spinel transition. The width of the phase loop was negligible for water contents less than about 1000 ppm, but then grew rapidly to become about 10 km wide, before shrinking again as the water content approaches ringwoodite saturation.

The study, published in Earth and Planetary Science Letters on April 14, was supported by the National Natural Science Foundation of China, PIFI from Chinese Academy of Sciences (CAS) and NERC Grants.

Phase boundary for post-spinel transition (top), and the width of the three-phase loop as a function of water content at 1873 K (bottom) (Image by IGCAS)

Reference: Joshua M.R. Muir, Feiwu Zhang, John P. Brodholt, The effect of water on the post-spinel transition and evidence for extreme water contents at the bottom of the transition zone, Earth and Planetary Science Letters, Volume 565, 2021, 116909, ISSN 0012-821X, https://doi.org/10.1016/j.epsl.2021.116909. (https://www.sciencedirect.com/science/article/pii/S0012821X21001680)

Provided by Chinese Academy of Sciences

New Material Could Harvest Water All Day Long (Material Science)

Micro-engineered, bioinspired design allows the material to collect moisture from cool fog as well as generating and collecting steam under sunny conditions

Tiny structures inspired by the shape of cactus spines allow a newly created material to gather drinkable water from the air both day and night, combining two water-harvesting technologies into one.

The material, a micro-architected hydrogel membrane (more on that later), can produce water through both solar steam-water generation and fog collection—two independent processes that typically require two separate devices. A paper about the material was published in Nature Communications on May 14.

Hydrogel trees
Images of representative fabricated PVA/PPy gel micro-tree array. Scale bar: 1 cm. © Caltech

Fog collection is exactly what it sounds like. At night, low-lying clouds along sea coasts are heavy with water droplets. Devices that can coalesce and collect those droplets can turn fog into drinking water.

Solar-steam generation is another water-collection technique. It works especially well in coastal areas because it is also capable of water purification, though it works during the day instead of at night. In the method, heat from the sun causes water to evaporate into steam, which can be condensed into drinking water.

Because the two technologies operate under such different conditions, they typically require different materials and devices to make them work. Now, a material developed at Caltech could combine them into a single device, working to generate clean water 24 hours a day.

“Water scarcity is a huge issue that humanity will need to overcome as the world’s population continues to grow,” says Julia R. Greer, the Ruben F. and Donna Mettler Professor of Materials Science, Mechanics and Medical Engineering and Fletcher Jones Foundation Director of the Kavli Nanoscience Institute. “Water covers three-quarters of the globe, but only about one half of one percent is available freshwater.”

Hydrogel tree
Images of an individual representative tree micro-topology. Scale bar: 1 mm. © Caltech

Greer has spent her career developing micro- and nano-architected materials; that is, materials whose very shapes (controlled at each length scale, nanoscopic and microscopic) give them unusual and potentially useful properties. In this case, Greer collaborated with Ye Shi, formerly a postdoctoral scholar at Caltech and now a postdoctoral scholar at UCLA, to create a membrane of arrayed tiny spines that resemble Christmas trees but are in fact inspired by the shape of cactus spines.

“Cacti are uniquely adapted to survive dry climates,” Shi says. “In our case, these spines, which we call ‘micro-trees,’ attract microscopic droplets of water that are suspended in the air, allowing them to slide down the base of the spine and coalesce with other droplets into relatively heavy drops that eventually converge into a reservoir of water that can be utilized.”

The spines are built out of a hydrogel; that is, a network of hydrophilic (water-loving) polymers that naturally attract water. Due to their tiny size, they can be printed onto a wafer-thin membrane. During the day, the hydrogel membrane absorbs sunlight to heat up water trapped beneath it, which becomes steam. The steam then recondenses onto a transparent cover, where it can be collected. During the night, the transparent cover folds up and the hydrogel membrane is exposed to humid air to capture fog. As such, the material can harvest water from both steam and fog.

In an operation test conducted during the night, samples of the materials ranging from 55–125 square centimeters in area were able to collect about 35 milliliters of water from fog. In tests during the day, the material was capable of collecting about 125 milliliters from solar steam.

The exact design of the membrane was created using the design program SolidWorks.

The hydrogel itself is a polyvinyl alcohol/polypyrrole (PVA/PPy) composite gel, a non-toxic and flexible material used in numerous applications including in capacitors, wearable strain and temperature sensors, and batteries.

To fine-tune the design of the micro-trees, Greer and Shi worked with Caltech’s Harry Atwater, Howard Hughes Professor of Applied Physics and Materials Science; and Ognjen Ilic, formerly a postdoctoral scholar at Caltech and now Benjamin Mayhugh Assistant Professor of Mechanical Engineering at the University of Minnesota.

Using computer modeling, Ilic computed the heat distribution within the micro-trees to help define the size and shape that would be most effective at drawing water from the air. With this successful proof-of-concept, the team now hopes to find a private partner capable of commercializing the technology for water-scarce regions.

“It is really inspiring that a relatively simple hydrophilic polymer membrane can be shaped in a morphology that resembles cacti spines and be capable of tremendous enhancement in water collection. I guess evolution really works,” Greer says.

The Nature Communications paper is titled “All-day Fresh Water Harvesting by Microstructured Hydrogel Membranes.” This work was supported by the Resnick Sustainability Institute, the Caltech Space Solar Power Project, the Joint Center for Artificial Photosynthesis (a U.S. Department of Energy Energy Innovation Hub), and served as a foundation for Greer’s subsequent Defense Advanced Research Projects Agency grant for the “Atmospheric Water Extraction” program, which is a collaboration with the University of Texas Austin and MIT.

Featured image: Porous structure of gel matrix © Caltech

Reference: Shi, Y., Ilic, O., Atwater, H.A. et al. All-day fresh water harvesting by microstructured hydrogel membranes. Nat Commun 12, 2797 (2021). https://doi.org/10.1038/s41467-021-23174-0

Provided by Caltech

Deep Water On Neptune and Uranus May Be Magnesium-rich (Planetary Science)

While scientists have amassed considerable knowledge of the rocky planets in our solar system, like Earth and Mars, much less is known about the icy water-rich planets, Neptune and Uranus.

In a new study recently published in Nature Astronomy, a team of scientists re-created the temperature and pressure of the interiors of Neptune and Uranus in the lab, and in so doing have gained a greater understanding of the chemistry of these planets’ deep water layers. Their findings also provide clues to the composition of oceans on water-rich exoplanets outside our solar system. 

Neptune and Uranus are conventionally thought to have distinct separate layers, consisting of an atmosphere, ice or fluid, a rocky mantle and a metallic core. For this study, the research team was particularly interested in possible reaction between water and rock in the deep interiors.

“Through this study, we were seeking to extend our knowledge of the deep interior of ice giants and determine what water-rock interactions at extreme conditions might exist,” said lead author Taehyun Kim, of Yonsei University in South Korea.

“Ice giants and some exoplanets have very deep water layers, unlike terrestrial planets. We proposed the possibility of an atomic-scale mixing of two of the planet-building materials (water and rock) in the interiors of ice giants.”

To mimic the conditions of the deep water layers on Neptune and Uranus in the lab, the team first immersed typical rock-forming minerals, olivine and ferropericlase, in water and compressed the sample in a diamond-anvil to very high pressures. Then, to monitor the reaction between the minerals and water, they took X-ray measurements while a laser heated the sample to a high temperature.

The resulting chemical reaction led to high concentrations of magnesium in the water. Based on these findings, the team concluded that oceans on water-rich planets may not have the same chemical properties as the Earth’s ocean and high pressure would make those oceans rich in magnesium.

“We found that magnesium becomes much more soluble in water at high pressures. In fact, magnesium may become as soluble in the water layers of Uranus and Neptune as salt is in Earth’s ocean,” said study co-author Sang-Heon Dan Shim of Arizona State University’s School of Earth and Space Exploration.    

A diamond-anvil (top right) and laser were used in the lab on a sample of olivine to reach the pressure-temperature conditions expected at the top of the water layer beneath the hydrogen atmosphere of Uranus (left). In this experiment, the magnesium in olivine dissolved in the water. Credit: Shim/ASU

These characteristics may also help solve the mystery of why Uranus’ atmosphere is much colder than Neptune’s, even though they are both water-rich planets. If much more magnesium exists in the Uranus’ water layer below the atmosphere, it could block heat from escaping from the interior to the atmosphere.

“This magnesium-rich water may act like a thermal blanket for the interior of the planet,” said Shim.

Beyond our solar system, these high-pressure and high-temperature experiments may also help scientists gain a greater understanding of sub-Neptune exoplanets, which are planets outside of our solar system with a smaller radius or a smaller mass than Neptune.

Sub-Neptune planets are the most common type of exoplanets that we know of so far, and scientists studying these planets hypothesize that many of them may have a thick water-rich layer with a rocky interior. This new study suggests that the deep oceans of these exoplanets would be much different from Earth’s ocean and may be magnesium-rich.

An electron microscopy image of the olivine sample shows a large empty dome structure where magnesium under high-pressure water precipitated as magnesium oxide. Credit: Kim et al.

“If an early dynamic process enabled a rock–water reaction in these exoplanets, the topmost water layer may be rich in magnesium, possibly affecting the thermal history of the planet,” said Shim.

For next steps, the team hopes to continue their high-pressure/high-temperature experiments under diverse conditions to learn more about the composition of planets.

“This experiment provided us with a plan for further exploration of the unknown phenomena in ice giants,” said Kim.

Additional authors of this study include Stella Chariton and Vitali Prakapenka of the University of Chicago; Anna Pakhomova and Hanns-Peter Liermann of the Deutsches Elektronen Synchrotron, Germany; Zhenxian Liu of the University of Illinois, Chicago; Sergio Speziale of the German Research Center for Geosciences, Germany; and Yongjae Lee of Yonsei University, South Korea.

Featured image: Uranus, taken by the NASA spacecraft Voyager 2. This ice giant, which is the seventh planet from the sun in our solar system, is nearly four times larger than Earth, and most of its mass is a dense fluid above a rocky core. Image by NASA/JPL

Reference: Kim, T., Chariton, S., Prakapenka, V. et al. Atomic-scale mixing between MgO and H2O in the deep interiors of water-rich planets. Nat Astron (2021). https://doi.org/10.1038/s41550-021-01368-2

Provided by Arizona State University

In The Core Much Of The Earth’s Water (Earth Science)

Using devices called diamond anvil cells, a team of researchers simulated the formation of the Earth’s core, demonstrating for the first time that, under extreme conditions of temperature and pressure, hydrogen can bind to the iron it contains. A result that supports the hypothesis that much of the water that arrived on Earth billions of years ago could be contained in the outer core in the form of hydrogen

According to a new study published in the pages of the journal Nature Communications , most of our planet’s water could be found inside it, dissolved in the iron and silicates of the outer core and mantle, respectively .

Given the extreme depths, temperatures and pressures involved, studying the heart of our planet directly is impossible. Much of the information we have today about its structure, composition and density has been obtained indirectly thanks to seismology – a branch of geophysics that studies the ways of propagation of seismic waves within the earth – and through laboratory experiments.

Thanks to this data, we know that the core is mainly made of iron and that its density, particularly that of the liquid outer core, is lower than expected. This has led the researchers to believe that, alongside the iron, there must be an abundance of some other light chemical element in the core. One possibility is that this element could be hydrogen: according to some hypotheses, the one contained in the water that reached Earth billions of years ago, during the numerous astronomical impacts.

To shed light on this possibility, a team of researchers from the University of Tokyo examined the behavior of water in the presence of iron and silicate compounds, using high temperature and high pressure experiments conducted inside anvil cells of diamond , thus simulating the metal-silicate reactions (core-mantle) that occurred during the formation of the Earth. “At the temperatures and pressures we are used to on the surface, hydrogen does not bind to iron” explains Shoh Tagawa, post-doc at the Department of Earth and Planetary Sciences of the University of Tokyo and first author of the study. “We wondered if this link can take place in more extreme conditions. Such extreme temperatures and pressures are not easy to reproduce and the best way to achieve them in the laboratory is to use a diamond anvil cell, a device that can produce pressures of 30-60 gigapascals at temperatures of 3,100-4,600 kelvins – a good simulation of the formation of the Earth’s core ».

Diamond anvil cell.  On the left, the chamber into which the samples are placed under conditions of pressure and temperature similar to those of the outer core of the Earth.  On the right, the diamonds of the anvil.  Credits: 2021 Hirose et al.

The team of scientists, led by  Kei Hirose of Kyoto University , used in particular iron and silicate compounds similar to those found in the Earth’s core and mantle respectively, which they compressed in the special chamber and simultaneously heated with a laser. To see what was happening in the sample, they used high-resolution images produced by applying a technique called secondary ion mass spectroscopy .

What happened during the experiment is that when the water met the iron and the molten silicates inside the anvil cell, the hydrogen of the water molecules reacted mainly with the iron, thus acting as a siderophilic element . while oxygen has entered the composition of the silicates.

The results obtained, explain the researchers, show for the first time that hydrogen can bind strongly with iron even in the extreme conditions of the Earth’s core, supporting the hypothesis that most of the water that arrived on Earth during its formation could be stored in this layer in the form of hydrogen. The presence of hydrogen in this layer could also explain its reduced density compared to pure iron.

“This discovery allows us to explore something that concerns us very much,” concludes Hirose. “The fact that hydrogen is a high-pressure siderophile tells us that much of the water that came to Earth during its formation through astronomical impacts may now be present in the core as hydrogen. We estimate that there could be as much hydrogen enclosed there as 70 oceans . If this had remained on the surface as water, our planet would have had no land and life as we know it would never have evolved ».

Featured image: The internal structure of the Earth. Credits: Wikipedia.

To know more:

Provided by INAF

Where On Earth is All The Water? (Earth Science)

There may be up to 70 times more hydrogen in Earth’s core than in the oceans

High-temperature and high-pressure experiments involving a diamond anvil and chemicals to simulate the core of the young Earth demonstrate for the first time that hydrogen can bond strongly with iron in extreme conditions. This explains the presence of significant amounts of hydrogen in the Earth’s core that arrived as water from bombardments billions of years ago.

Given the extreme depths, temperatures and pressures involved, we are not physically able to probe very far into the earth directly. So, in order to peer deep inside the Earth, researchers use techniques involving seismic data to ascertain things like composition and density of subterranean material. Something that has stood out for as long as these kinds of measurements have been taking place is that the core is primarily made of iron, but its density, in particular that of the liquid part, is lower than expected.

Left. A metal cylinder with colored dots on its top. Right. Two jewels meeting at a point.
Diamond anvil. The outer metal casing and inner diamond teeth of the high-pressure anvil. © 2021 Hirose et al.

This led researchers to believe there must be an abundance of light elements alongside the iron. For the first time, researchers have examined the behavior of water in laboratory experiments involving metallic iron and silicate compounds that accurately simulate the metal-silicate (core-mantle) reactions during Earth’s formation. They found that when water meets iron, the majority of the hydrogen dissolves into the metal while the oxygen reacts with iron and goes into the silicate materials.

“At the temperatures and pressures we are used to on the surface, hydrogen does not bond with iron, but we wondered if it were possible under more extreme conditions,” said Shoh Tagawa, a Ph.D. student at the Department of Earth and Planetary Science at the University of Tokyo during the study. “Such extreme temperatures and pressures are not easy to reproduce, and the best way to achieve them in the lab was to use an anvil made of diamond. This can impart pressures of 30–60 gigapascals in temperatures of 3,100–4,600 kelvin. This is a good simulation of the Earth’s core formation.”

A large office of electronic items. A man sitting at a computer desk.
Isotope imaging lab at Hokkaido University. The research was a collaboration between institutions, including Hokkaido University. © 2021 Hisayoshi Yurimoto

The team, under Professor Kei Hirose, used metal and water-bearing silicate analogous to those found in the Earth’s core and mantle, respectively, and compressed them in the diamond anvil whilst simultaneously heating the sample with a laser. To see what was going on in the sample, they used high-resolution imaging involving a technique called secondary ion mass spectroscopy. This allowed them to confirm their hypothesis that hydrogen bonds with iron, which explains the apparent lack of ocean water. Hydrogen is said to be iron-loving, or siderophile.

“This finding allows us to explore something that affects us in quite a profound way,” said Hirose. “That hydrogen is siderophile under high pressure tells us that much of the water that came to Earth in mass bombardments during its formation might be in the core as hydrogen today. We estimate there might be as much as 70 oceans’ worth of hydrogen locked away down there. Had this remained on the surface as water, the Earth may never have known land, and life as we know it would never have evolved.”

Featured image: Sample from high-pressure experiment. High-resolution chemical analyses with secondary ion mass spectroscopy showed the abundance of water left in silicate melt after compressing with liquid iron metal. © 2021 Tagawa et al.


Shoh Tagawa, Naoya Sakamoto, Kei Hirose, Shunpei Yokoo, John Hernland, Yasuo Ohishi, and Hisayoshi Yurimoto, “Experimental evidence for hydrogen incorporation into Earth’s core.,” Nature Communications: May 11, 2021, doi:10.1038/s41467-021-22035-0.
Link (Publication)

Provided by University of Tokyo

Earth May Have Been A Water World 3 Billion Years Ago (Planetary Science)

Harvard scientists calculate early ocean may have been 1 to 2 times bigger

In 1995, Universal Studios released what was, at the time, the most expensive movie ever made: “Waterworld,” a film set in the distant future where the planet Earth was almost completely covered in water and its remaining inhabitants could only dream of mythic dry land. Well, take away the future part, the exorbitant budget, the chain-smoking pirates, and the gill-sporting Kevin Costner and the movie may have been onto something.

According to a new, Harvard-led study, geochemical calculations about the interior of the planet’s water storage capacity suggests Earth’s primordial ocean 3 to 4 billion years ago may have been one to two times larger than it is today, and possibly covered the planet’s entire surface.

“It depends on the conditions and parameters we look at in the model, such as the height and distribution of the continents, but the primordial ocean could have flooded more than 70, 80, and even 90 percent of the early continents,” said Junjie Dong, a Ph.D. student in Earth and Planetary Sciences at the Graduate School of Arts and Sciences, who led the study. “In the extreme scenarios, if we have an ocean that is two times larger than the amount of water we have today, that might have completely flooded the land masses we had on the surface of the early Earth.”

The research was published in AGU Advances earlier this month. It challenges long-held assumptions that Earth’s ocean volume hasn’t changed too much since the planet’s formation. At its root, the paper delves into understanding the origins of water and the history of how its bodies have evolved.

Rebecca A. Fischer.
“There’s not really anywhere that water could come from besides the oceans on the surface, so that implies that the oceans had to have been larger in the past,” said Rebecca Fischer, co-lead author of the study. Rose Lincoln/Harvard file photo

“In the geology community, biology community, and even in the astronomy community, they are all interested in the origins of life, and water is one of the most important key elements that has to be considered,” Dong said.

Researchers weren’t looking for signs of liquid water, but its chemical equivalent, oxygen and hydrogen atoms, which bond to the interior of the planet. They compiled all the data in the scientific literature they could find on minerals that hold these signs and used the figures to calculate how much water there could be in the Earth’s mantle, which makes up the bulk of the planet’s interior. That number is referred to as the planet’s mantle water storage capacity. It changes as the interior of the planet continues to cool.

The group calculated what that number could be today and how much could have been stored a few billion years ago to see how the number had changed. The capacity back then was significantly less.

Scientists then compared those numbers to geochemical estimates of how much water is in the mantle today. Analysis found that the actual water content today is likely higher than the maximum water capacity of the mantle a few billion years ago, meaning the water today wouldn’t have been able to fit in the mantle billions of years ago. This suggests the water was someplace else — on the world’s surface. According to the researchers’ calculations, the amount of water that could have gone down into the Earth’s mantle could potentially be as much as all the present-day oceans combined.“In the geology community, biology community, and even in the astronomy community, they are all interested in the origins of life, and water is one of the most important key elements that has to be considered.”— Junjie Dong, Ph.D. student in Earth and Planetary Sciences

“There has been water falling into the Earth’s interior over time, which makes sense because with plate tectonics you have some of the plates on the Earth’s surface that subduct and go down into the interior and bring water down with them,” said Rebecca Fischer, the Clare Boothe Luce Assistant Professor of Earth and Planetary Sciences and the study’s other lead author. “There’s not really anywhere that water could come from besides the oceans on the surface, so that implies that the oceans had to have been larger in the past.”

The study isn’t the first to suggest Earth could have been a water world, but the researchers believe it to be the first offering quantitative evidence based on the water storage capacity of the mantle.

The researchers point out some caveats in the study, the main one being that data on the minerals used to determine the amount of water in the planet’s mantle is limited when it comes to its deeper parts, which go down thousands of kilometers.

In their next project, Dong and Fischer are looking toward Mars. They plan to use a similar model to determine the amount of water that could have been stored in its interior.

“Evidence seems to point out that the early Mars had a significant amount of water on its surface,” Dong said. “We want to investigate whether that surface water had some relations with the water that could possibly have been stored in its interior.”

This study was supported by the National Science Foundation, the European Research Council, and a James Mills Pierce Fellowship from the Graduate School of Arts and Sciences.

Featured image: Calculations show that Earth’s oceans may have been 1 to 2 times bigger than previously thought and the planet may have been completely covered in water.  Credit: Alec Brenner/Harvard University

Reference: Dong, J., Fischer, R. A., Stixrude, L. P., & Lithgow‐Bertelloni, C. R. (2021). Constraining the volume of Earth’s early oceans with a temperature‐dependent mantle water storage capacity model. AGU Advances, 2, e2020AV000323. https://doi.org/10.1029/2020AV000323

Provided by Harvard Gazette

Cleaner Water Through Corn (Chemistry)

Activated carbon made from corn stover filters 98% of a pollutant from water

Corn is America’s top agricultural crop, and also one of its most wasteful. About half the harvest—stalks, leaves, husks, and cobs— remains as waste after the kernels have been stripped from the cobs. These leftovers, known as corn stover, have few commercial or industrial uses aside from burning. A new paper by engineers at UC Riverside describes an energy-efficient way to put corn stover back into the economy by transforming it into activated carbon for use in water treatment. 

An illustration depicting how corn stover is turned to biochar, then to activated carbon for water filtration. (Abdul-Aziz et. al., 2021)

Activated carbon, also called activated charcoal, is charred biological material that has been treated to create millions of microscopic pores that increase how much the material can absorb. It has many industrial uses, the most common of which is for filtering pollutants out of drinking water. 

Kandis Leslie Abdul-Aziz, an assistant professor of chemical and environmental engineering at UC Riverside’s Marlan and Rosemary Bourns College of Engineering, runs a lab devoted to putting pernicious waste products such as plastic and plant waste known as biomass back into the economy by upcycling them into valuable commodities. 

“I believe that as engineers we should take the lead in creating approaches that convert waste into high-value materials, fuels and chemicals, which will create new value streams and eliminate the environmental harm that comes from today’s take-make-dispose model,” Abdul-Aziz said. 

Abdul-Aziz, along with doctoral students Mark Gale and Tu Nguyen, and former UC Riverside student Marissa Moreno at Riverside City College, compared methods for producing activated carbon from charred corn stover and found that processing the biomass with hot compressed water, a process known as hydrothermal carbonization, produced activated carbon that absorbed 98% of the water pollutant vanillin.

Hydrothermal carbonization created a biochar with higher surface area and larger pores when compared to slow pyrolysis- a process where corn stover is charred at increasing temperatures over a long period of time. When the researchers filtered water into which vanillin had been added through the activated carbon, its combination of larger surface area and bigger pores enabled the carbon to absorb more vanillin.

“Finding applications for idle resources such as corn stover is imperative to combat climate change. This research adds value to the biomass industry which can further reduce our reliance on fossil fuels,” Gale said.

The paper, “Physiochemical properties of biochar and activated carbon from biomass residue: influence of process conditions to adsorbent properties,” is published in ACS Omega.

Provided by University of California Riverside

Why The Search For Life, Probably, Requires The Search For Water? (Planetary Science)

Friends, there are several papers you may have read, which focuses on the search for extraterrestrial life that claim, either directly or indirectly, that life (including Earth’s) forms in the absence of water. But according to Modirrousta–Galian and Maddalena, this argument is incompatible with most lines of evidence and data.

“Liquid water is essential to life and should be the direction to follow in future space flight missions to improve the likelihood of finding extraterrestrial life.”

In order to tackle this argument, they breakdown water properties to the physical, chemical and biological level and demonstrated that it is the most adequate medium for the formation of life.

1) Cosmochemical level

By shedding light on the cosmochemical composition of our solar system, they showed, how common water is in the Universe as the two elemental constituents of water, hydrogen and oxygen, are the first and third most common elements (as you can see in table below).

Table 1: The cosmochemical composition of our solar-system according to Lodders. © Modirrousta-Galian & Maddalena

“It follows that from a purely statistical perspective a strong argument can be made that if life were to exist elsewhere in the universe, it would have most probably interacted with water in a certain manner.”

2) Planetary Level

In our solar system the condensation temperature of H2O is ∼ 150 K, which corresponds to a distance of approximately ∼ 3 AU from the Sun. This location is called the ‘frost line’ and its properties will vary depending on the nature of the protoplanetary disc from which the planet forms as well as the spectral type of the host star.

According to Modirrousta–Galian and Maddalena, for planets that formed at temperatures below ∼ 150 K, there is a very high probability that water is present in large amounts, such as Uranus and Neptune that are rich in water ice. In contrast, planets that formed at hotter temperatures are unlikely to have a significant abundance of water unless it came from external sources.

“This is the strong evidence that the delivery of water by comets and asteroids could be common not just in our solar system, but elsewhere in the universe. In other words, due to the copious cosmic presence of water, whether a planet formed within or outside of the frost line appears to have little influence on whether it has come in contact with water.”

But, though the delivery of water is common in the universe, the presence of water on planetary surfaces depends on their thermodynamic stability, how close they orbit to their host star etc etc.

3) Micropalaeontological Level

They also mentioned that the proportion of Earth’s ‘dry’ surface has been investigated is much greater than the equivalent for Earth’s oceans meaning that there is a bias that has to be accounted for. Even still, the oldest known microfossils have been found in the oceans. In addition, considering that most of Earth’s surface is covered by water (approximately 70%), it must be acknowledged that there is a strong statistical argument for life’s oldest fossils being located underwater.

4) Physiochemical level

The ‘wet-dry’ hypothesis suggests that water was a catalyst for the formation of primordial cells in the early-Earth due to the prevalence of hydrolysis-condensation reactions found in nature. However, according to Modirrousta–Galian and Maddalena, this description is unable to fully encapsulate the unique physicochemical properties of water, which may be crucial for abiogenesis. For this, they attained more holistic analysis by considering the electronic properties of a H2O molecule.

Figure 2: The physicochemical properties of water can be explained by the high electronegativity of oxygen, and the low electronegativity of hydrogen, which give it two dipoles capable of hydrogen bonding. The polar nature of the molecule is due to the 104.5° angle which forms. © Modirrousta-Galian & Maddalena

According to authors, the highly polar nature of water makes it a universal solvent allowing it to dissolve a large range of inorganic and organic molecules. Wet-dry cycles taking place on mineral deposits would benefit from this property as they can solubilise metal ions such as iron and arsenic, which were relatively abundant in the early Earth.

“The varying redox states of these metals allows them to transfer electrons to other molecules and act as a source of energy. Dissolution of these metal ions is an example of how the polar behaviour of water facilitated primordial reactions.”

The dielectric constant of water is also very high (with a value of 81) and it is responsible for weakening the bonds between other molecules such as metal salts in minerals.

Hydrophobicity is another physicochemical property that is important in sustaining life. This behaviour is crucial to forming an enclosed membrane, a prerequisite to forming enclosed cellular life. A semi-permeable barrier provides a means to control the movement of molecules, either produced inside the cell, such as proteins, or carried into the cell, such as metal ions. In aqueous solutions, amphiphilic molecules (containing one charged hydrophilic end and one hydrophobic moiety) will form liposomes, micelles or bilayers as the most thermodynamically favourable structure (Fig. 3). This is because these shapes reduce the surface area in contact with water, minimising the free energy of the system.

Figure 3: The most thermodynamically favourable shapes for amphiphilic molecules to take in water are micelles, bilayer sheets and liposomes. These forms are driven by the hydrophobic effect and may have facilitated the evolution of cellular membranes. © Modirrousta-Galian & Maddalena

The high electronegativity of oxygen, in the molecular structure of water, allows it to form hydrogen bonds (Fig. 3B). These can form between other water molecules, or with other molecules containing highly electronegative atoms, such as peptides. Hydrogen bonds play a chaperone-like role in biomolecular topography, meaning that they assist in the process of folding biological molecules such as proteins and DNA. The shape of these molecules are key to regulating processes inside and outside of the cell. For example, an enzyme has a very precise and defined shape that dictates the biochemical functions it has. As protein folding takes place, water forms hydrogen bonds with peptides in a rapid cycle of breaking and reforming, following a folding-funnel mechanism. This mechanism causes the potential and configurational energy of a protein to decrease as its native state is approached, following a funnel-like direction as various folding conformations are trialled.

“It is the polar nature of water that allows for this process to take place. Without hydrogen bonding and water as a solvent to chaperone, proteins would have an extensive number of probable folding patterns, leading to imprecise folding or no folding at all. This may result in a complete loss of function.”

For more, read..

Darius Modirrousta-Galian, Giovanni Maddalena, “Of Aliens and Exoplanets: Why the search for life, probably, requires the search for water”, arxiv, pp. 1-5, 2021. https://arxiv.org/abs/2104.01683

Copyright of this article (editing) totally belongs to our author S. Aman. One is allowed to reuse it only by giving proper credit either to him or to us