The Earth Story

Fluorescent Plants – what the remote sensing instruments see

Our eyes are adapted to only see particular wavelengths of the electromagnetic spectrum (light in the visible spectrum) despite there being many more wavelengths of light out there, ranging from radio waves to gamma rays. Many remote sensing satellites have sensors specifically designed to capture light outside of the visible part of the spectrum which can help further our understanding of the planet.

Fluorescence of plants is an example of the measurements that some satellites (ASTER, Landsat, Terra and more) can take to help understand our planet more. Fluorescence is the emission of light by a substance that has absorbed light or electromagnetic radiation and in the case of plants, it is infrared light that is emitted as fluorescence. This is useful for us to measure, as you can derive the rate of photosynthesis and health of vegetation from satellite data now. The amount of fluorescence that plants emit is directly proportional to how much photosynthesis they are doing, which ultimately allows us to know how much CO2 plants are removing from our atmosphere.

Using the same remote sensing instruments, it is possible to determine the overall health of vegetation remotely using what is known as reflectance curves. Different surface compositions (colour, structure, texture and chemical composition) result in different reflectance curves Vegetation peaks in its reflectance at about 850nm, of which healthy vegetation has a reflectance value of up to 40%. Stressed vegetation has a reflectance value of up to roughly 15%, allowing us to analyse the overall vegetation health.

Further knowledge on this will help climate modellers in their predictions, scientists studying plants reactions to various events (i.e. droughts) and even farmers.

-MJA

Further reading: Fluorescence: http://climate.nasa.gov/blog/2259

Vegetation health: http://bit.ly/1avDZTB

Image credit: NASA. Check out their videos of plant photosynthesis happening (the image is a screengrab from one of them):

Eating Light

A small green sea slug, Elysia chlorotica, or the emerald green elysia, has incorporated bits of algae into their cells to help produce food, becoming an animal plant hybrid. More precisely, the slug has managed to harness the chloroplasts in algae to create food from sunlight through photosynthesis, something scientists would have never guessed until this organism was found.

Although capable of staying alive in the laboratory for months at a time with sufficient sunlight, sea slugs normally feed on algae by eating the cytoplasm of the cells and protein from various plants. Some slugs store the chloroplasts found in the cytoplasm in large digestive glands, sometimes for months at a time. What scientists didn't know, until recently, was that the slugs actually use these chloroplasts to create food.

In order to use chloroplasts, algal DNA that creates proteins that activate the chloroplasts would also need to be present. Various research teams were unable to find that DNA. But a new study from the Marine Biological Laboratory in Massachusetts and published in the Biological Bulletin used fluorescent DNA markers to track the algal genes.

It appears that the transferred genes are responsible for repairing damaged chloroplasts and are passed from one generation of sea slugs to the next. When the sea slug runs out of fresh algae to eat, they use the chloroplasts to create food until they can find more algae.

This case has been proposed to be the first example of transfer of genes from one organism to another. However, because these organisms appear to be becoming increasingly rare over the past few years, many researchers have stopped working on them.  Further reading: http://www.biolbull.org/content/227/3/300.abstract

and

http://bit.ly/1EdYw7S https://www.nationalgeographic.com/animals/2018/07/solar-powered-photosynthetic-sea-slugs-in-decline-news/

Illustration credit: https://commons.wikimedia.org/wiki/File:Elysia-chlorotica-body.jpg

-Colter

Delightful Diatoms Diatoms are a type of photosynthesising (although some are heterotrophic) algae which are found in almost every aquatic environment; from fresh and marine waters to soils. Diatoms are microscopic, most falling in the range of 20 to 200 microns (0.02-0.2 mm) in diameter or length. But don’t underestimate them. Diatoms play a fundamental role in aquatic ecosystems. In the ocean itself, the oxygen given off by diatoms (and plants) supports the majority of other marine life. Without this oxygen, the water would be uninhabitable and stagnant. Diatoms are also the basis of many food chains within aquatic environments and indirectly provide a food source for us terrestrial beings. These tiny algae also provide approximately 25% of the oxygen we breathe- the greatest gift of all! They are also quite a diverse group, as you can see in this image. Their siliceous wall can be highly patterned with a variety of pores, ribs, minute spines, marginal ridges and elevations; all of which can be used to delineate genera and species. There are more than 200 genera of living diatoms, and it is estimated that there are approximately 100,000 extant species ranging in shape from circular, triangular, square, or elliptical. -Jean Photo courtesy of wikimedia commons.

The colours of autumn

Deciduous trees are those that shed their leaves every year, as opposed to the evergreens, which do not. While the latter are often associated with conifers, one should remember that there are varied other trees such as oaks with species that keep their leaves year round. The former is associated with trees that live or evolved in regions with a long dark and cold winter, and leaf shedding is a mechanism to conserve energy in the face of temperatures cold enough to freeze off the leaves and too little light to make photosynthesis worthwhile while still facing the threats of ice and wind. As light levels and day length diminish, hormonal cascades pass through the trees, which start to withdraw metabolically expensive chemicals such as green chlorophyll and red orange opsins into their depths, eventually taking most of the sap out of the periphery as well.

The peripheral branches are then left in suspended animation while the vitality of the tree focusses back into the rootball, which outside permafrost zones at least is kept insulated by the covering blanket of soil. The process is not instantaneous, and the chemicals are withdrawn in sequences before the husk of the leaf is allowed to fall off, becoming insulating mulch for the base of the tree, and slowly releasing its remaining nutrients back into the soil (which is why excessive dead leaf removal by humans is not necessarily the best thing for the trees while conforming to most people’s aesthetics). Here we have a maple from Japan from the Acer family caught at the stage where nearly all the chlorophyll is gone but the red opsins remain in all their intense glory.

Loz

Image credit: Falcor88

This cool visualisation by #NASA shows photosynthetic activity across North America during the growing season, which is of course coming to an end. During photosynthesis, plants absorb sun light, but also re-emit some of that light as a faint but measurable glow that is undetectable to human eyes.

Thanks to the capabilities of the Global Ozone Monitoring Instrument 2 (GOME-2) instrument on Metop-A, a European meteorological satellite, we are able to detect this faint fluorescence.

As you can imagine, it is difficult to distinguish between fluorescent signals from the vantage point of outer space, but luckily, photosynthetic vegetation has a unique spectral signature that can be isolated; a plant fingerprint, so to speak.

The pink glow in the satellite photo represents fluorescence measured from land plants in early July, from 2007 to 2011 and the magnitude of the glow indicates the amount of photosynthesis within a given region.

Impressive!

-Jean

For more information and an awesome video, head on over to NASA's site here:http://1.usa.gov/1iCDEjC

Meet David Latimer and his 58 year old bottle garden- We like David.

On Easter Sunday in 1960, David, using a ten gallon carboy, decided to make a bottle garden. He filled the vessel with compost, about 200ml of water and then delicately lowered in a spiderwort seedling (Tradescantia) using a piece of wire. He then placed the bottle near a window and let nature take over.

12 years later, David introduced another small amount of water, closed the container and it hasn't been open since.

As you can see from the image, David’s bottle garden is thriving, but how has it flourished so much?

David has had very little to do with it. Photosynthesis and cellular respiration are really running the show; there is an entirely self-sufficient ecosystem at play here, with sufficient nutrient recycling. The plants release oxygen and offer decaying plant litter, which allows soil microorganisms to flourish. The microorganisms (as well as the plants at night) release CO2 through cellular respiration which is utilised by the plants. The water within the bottle is taken up by the plant roots and is then released back into air during transpiration and then condenses back down into the soil where the process starts again.

Talk about low maintenance!

The bottle stands on display under the stairs in the hallway of his home in Cranleigh, Surrey, England.

David plans to pass it on to his children after he is gone or if they do not want it, he will leave it to the Royal Horticultural Society.

If that fails, I'll take it!

-Jean

If you would like to make your own bottled garden, here’s some tips: http://www.instructables.com/id/Bottle-Garden/

For those of you in the Northern Hemisphere who were lucky enough to have a summer this year (we didn’t have much of one here in Ireland), it’s time to say goodbye!

Today, the 22nd of September, is the first day of autumn, also known as the autumnal equinox.

The term “equinox” is derived from an astronomical event in which the sun transits directly over the Earth’s equator. Day and night are approximately equal length on equinoxes, which is how the days got their name — it means "equal night" in Latin.

From today, the days will start to shorten in the Northern Hemisphere as winter approaches.

A sure sign of the onset of autumn can be seen in the leaves of trees. During the spring and summer the leaves have served as factories where most of the foods necessary for the tree's growth are manufactured. The process, known as photosynthesis; takes place in the leaf in numerous cells containing chlorophyll, which gives the leaf its green colour. Along with the green pigment are yellow to orange pigments; carotenes and xanthophyll, however most of the year these colours are masked by great amounts of chlorophyll.

In autumn, because of the changes in daylight hours and changes in temperature the leaves stop photosynthesising and hence the chlorophyll breaks down. The green colour disappears, and the yellow and orange colours become visible. At the same time other chemical changes may occur, which form additional colours through the development of red anthocyanin pigments.

This combination of beautiful colours makes for some fantastic scenery, as in this picture of Poulakerry Castle on the banks of the River Suir, Co. Tipperary, Ireland.

-Jean

Photo courtesy of Joe Cashin

Whiting This image of Lake Ontario was taken by the International Space Station Expedition 36 crew. It shows an example of a “whiting event.” Whiting occurs when an abundance of calcium carbonate particles form in water and is usually caused by changes in water temperature or an increase in photosynthesis by microscopic marine life. The increased photosynthesis reduces the amount of carbon dioxide in the water, which also changes the acidity and allows the calcium carbonate particles to form. Although the white milky appearance resembles a phytoplankton bloom, scientists on the ground studying the lake confirmed this particular case was a whiting event. -Amy Reference: http://visibleearth.nasa.gov/view.php?id=81952 Image Credit NASA

The leaf cycle:

During the spring and summer leaves serve as factories where most of the foods necessary for the tree's growth are manufactured. The process, known as photosynthesis; takes place in the leaf in numerous cells containing chlorophyll, which gives the leaf its green colour. Along with the green pigment are yellow to orange pigments; carotenes and xanthophyll, however most of the year these colours are masked by great amounts of chlorophyll.

In autumn, because of the changes in daylight hours and changes in temperature the leaves stop photosynthesising and hence the chlorophyll breaks down. The green colour disappears, and the yellow and orange colours become visible. At the same time other chemical changes may occur, which form additional colours through the development of red anthocyanin pigments.

Eventually the tree sheds the leaves to save nutrients and prevent loss of water, the leaves then rot and return to the soil as organic matter.

-Jean

Photo courtesy of Flickr user robherr.

Early Oxygen jump

Free oxygen first appeared in Earth’s atmosphere at least 2.5 billion years ago after single celled organisms figured out photosynthesis, but it wasn’t abundant. It took literally billions of years for oxygen to become the second most abundant gas in the atmosphere, as it is today.

The time of the major increase in oxygen is an important era in geologic history. In the last part of the Precambrian, known as the Neoproterozoic, there were two major glaciations that may have frozen over Earth entirely and life diversified rapidly – organisms went from being single-celled to multicellular with hard parts in a very short time, geologically speaking.

These events happening in short order – the major glaciations, large increase in oxygen, and development of complex life, have been thought of as generally linked through a well-understood mechanism. Glaciers erode lots of material from continents and would deliver nutrients to the ocean. Extra nutrients in the ocean would allow more photosynthesis, freeing up extra oxygen. Extra oxygen provides more easily accessible energy, promoting the development of complex life forms.

However, that sequence implies that the major glaciations came first. This plot comes from a newly published study led by researchers at Brock University,that found surprisingly high oxygen contents even before the major glaciations.

They measured the high oxygen contents trapped in salt crystals. When crystals grow they often have small gaps in them that can trap other phases as inclusions and hold them for long time periods. In the study, the scientists tested inclusions in the mineral halite (NaCl, literally table salt) from around the world and found that they accurately tracked oxygen contents in the atmosphere as far back as the Cretaceous. They then sampled 800 million year old halite from a drill core in Australia and found that those inclusions varied from 1 to 13% oxygen, values shown in the green bars – less than the modern atmosphere but much higher than thought based on previous model curves.

There isn’t an obvious chemical pathway to generate oxygen inside of a salt inclusion, so the scientists concluded that they had a sample showing oxygen was high much earlier than thought. This new data could explain earlier origins of multicellular life as has recently been found in some fossils, but it leaves us confused now as the glaciations were a great explanation for why oxygen shot upward. It could have gone the other way – if CO2 was being used up in photosynthesis then that could have been a major trigger for the glaciations, but this study leaves no obvious reason why such big changes would have happened 800 million years ago.

This is a particularly useful piece of data, and it leaves us now working to solve another major puzzle regarding how multicellular life was able to evolve on this planet.

-JBB

Image credit and original paper: Blamey et al., 2016 http://bit.ly/2avdRJH

Both of these things can’t be right: part 1.

Over the last 2 weeks, there was an interesting crossing of new results in geology; two distinct methods telling entirely different stories about the planet Earth. One in particular got a lot of press coverage. But, if you actually delve deeply into the science, there’s something really neat about the combo; both of these papers cannot simultaneously be right. Their results fundamentally disagree. Let’s explore why.

When the planet Earth formed, its atmosphere had basically no oxygen. It was dominated by gases like methane and carbon dioxide. About 3 billion years ago, life started figuring out methods of photosynthesis that gave off oxygen as a byproduct; when that oxygen was released it would react with the surrounding environment and start using up the other gases. Then, 2.5 billion years ago or so, the planet fundamentally changed; oxygen contents in the atmosphere began to rise from zero to the values we see today, fundamentally changing the chemistry of the surface of our planet.

This period is known as the “Great Oxygenation Event” or GOE and it is such a major change that it is one of the biggest boundaries on the geologic timeline, separating the Archean from the Proterozoic.

One of our best indicators for this change is actually recorded in isotopes of sulfur, found especially in the mineral pyrite (FeS2) trapped in sedimentary rocks from that time. Sulfur has 4 important stable isotopes, with masses 32, 33, 34, and 36. Compared to sulfur 32, the others have 1, 2, and 4 extra neutrons, respectively, so their masses go up by 1, 2, and 4.

Isotopic processes care a lot about these mass differences. When a process changes the stable isotopes of a compound, the bigger the mass difference, the bigger the effect. Because 33 Sulfur has 1 extra neutron and 34 Sulfur has 2, anything that changes the abundances of these isotopes should affect 34 Sulfur twice as much. Similarly, 36 Sulfur should be affected twice as much as 34 Sulfur because 34 sulfur has 2 extra neutrons and 36 sulfur has 4.

This type of behavior is what we call a “mass dependent fractionation”. Most processes on Earth are like this; when water evaporates, it undergoes mass dependent fractionations. When sulfur forms acid rain by interacting with water in the atmosphere, it undergoes mass dependent fractionations.

When geologists look at rocks going back over 2 billion years, they find this rule holds. Sulfur basically undergoes only mass dependent fractionations to a good approximation; 36 goes up four times for every 2 times 34 goes up, and so on. But, when oxygen vanishes from the atmosphere, something fundamentally different happens.

Sulfur can also be broken apart by energy from the sun. If sulfur is high enough in the atmosphere, solar energy will ionize it and the energy of light that ionizes the sulfur depends on the exact mass of the nucleus. This process ionizes sulfur 33, 34, and 36 evenly, but doesn’t ionize sulfur 32 very much as it’s by far the most abundant isotope and there isn’t enough sunlight to ionize all of it.

This process produces a pool of ionized sulfur 33, 34, and 36 that sinks down to the surface to form pyrite, without any extra sulfur 32. This process can therefore change the ratios of these isotopes, but it does so without caring what their masses are; it only cares that they’re different. This is called a “Mass Independent Fractionation” since it no longer cares about whether they differ by 2 or 4 mass units.

This photo-chemical reaction in the atmosphere has a consequence. When it happens, the ionized sulfur rains down, producing pyrite in the ocean that no longer has the simple, mass-dependent ratios. For the last >2 billion years, pyrite in the oceans has had those fixed ratios of isotopes, but in the Archaean the ratios change a lot. Change the winds on one day, change the place the sulfur hits the ocean, and the isotopic composition of the pyrite changes.

This on/off switch in the ocean pyrite correlates with the rise of oxygen. Oxygen and ozone molecules in the atmosphere can absorb light at the same wavelengths that ionize sulfur. If there is oxygen in the upper atmosphere, the light required to ionize the sulfur is blocked before it reaches the surface, so the end of this mass-independent sulfur behavior should mark the Great Oxygenation Event.

Using sediment cores through ancient rocks in South Africa, a research team led by Dr. Luo from MIT was able to pinpoint a narrow range of sediments where this isotope signature was present and then suddenly absent. This just-published result constrains the end of sulfur mass-independent behavior to have happened 2.33 billion years ago.

If this mechanism works as we understand it to work, then this group has not only found the exact date of the rise of oxygen, they’ve constrained that it happened very fast. The world must have gone from an oxygen-free to an oxygenated atmosphere in a period of less than 10 million years; very fast for one of the most dramatic changes on Earth.

That’s the story of the rise of oxygen as known only a couple weeks ago. In the next post I’ll cover a wrench thrown into this understanding, and how what I presented here is simply incompatible with these new results.

-JBB

Image credit: NASA/ISS/Ron Garan http://go.nasa.gov/1TvNPI2

Original paper/Press Release: http://advances.sciencemag.org/content/2/5/e1600134.full http://bit.ly/1TvNaGt

Other references: http://bit.ly/1sHybPZ http://bit.ly/1sHyFFL http://bit.ly/20gLCk8 http://bit.ly/1W752K3

The formation of Earth’s atmosphere:

Almost all of life on Earth is sustained by oxygen. Comprised of two oxygen atoms, the gaseous form of oxygen is held together by a strong double bond (O2). Oxygen is crucial for respiration, a metabolic process whereby organisms convert carbohydrates into energy, with carbon dioxide being a by-product.

4.6 billion years ago, when Earth was formed, it consisted of nothing more than a rocky sphere, surrounded by an atmosphere of hydrogen and helium. Due to the lack of a magnetic field it is believed that this early atmosphere was subjected to harsh interstellar winds and radiation and it dissipated into space. The formation of many volcanoes, which accompanied the establishment of Earth’s crust, caused large amounts of gaseous compounds to be ejected into the atmosphere, such as ammonia, carbon dioxide and water vapour. The introduction of these new gases, however, would not support the modern diversity of life that we know.

3.3 billion years ago, bacteria arose, and cyanobacteria, a specialised type of bacterium began to dominate earth’s surface. Cyanobacteria are special in that they contain the same green, light-trapping pigment as plants: chlorophyll. The success of cyanobacteria set the stage for the evolution of life and the development of the atmosphere we know today. Chlorophyll is a pigment that allows an organism to harness the energy from the light of the sun by converting carbon dioxide into usable carbohydrates, a food source. Although requiring carbon dioxide, the process produced oxygen. Cyanobacteria became so prolific that they changed the entire composition of the earth’s atmosphere to an oxygen-rich one which would later be the foothold for life. Currently earth’s main atmospheric constituents are 21% oxygen and 78% nitrogen as well as smaller amounts of other gases such as water, argon and carbon dioxide.

Will life be responsible for the next major atmospheric transformation?

Renesh T

Acknowledgements:

Kashmira Raghu

Image credit http://www.geograph.org.uk/photo/3002724

References and Further Reading:

hyperphysics.phy-astr.gsu.edu/hbase/biology/celres.html www.universetoday.com/26659/earths-early-atmosphere/

Missing half billion

The first evidence of widespread oxygen in the atmosphere occurs in rocks that are about 2.5 billion years old. That time marks one of the major boundaries on the geologic timeline, the boundary between the Achaean and the Proterozoic. However, that time does not match up with the evolution of oxygen producing bacteria.

Geologic evidence indicates that organisms producing oxygen as a byproduct existed at least as early as 2.8 billion years ago, a gap of several hundred million years. That difference creates a geologic question; how was life generating oxygen if it didn’t build up in the atmosphere?

A team led by Dr. Dawn Sumner from UC Davis investigated a site in Antarctica called Lake Fryxell, in the Dry Valleys of Antarctica. This lake is permanently covered by about 5 meters of ice on average, thin enough for sunlight to get through but thick enough that the waters cannot exchange oxygen with the atmosphere.

The team drilled small cores through that layer of ice and widened it using copper heaters to allow divers into the lake. Those divers went deep enough to observe the environment at the bottom, where the environment goes anoxic (no free oxygen in the water).

In this environment, the scientists found surprising patches of green; the classic color of photosynthetic organisms. They investigated these patches and found that they were small batches of photosynthetic bacteria. During the long Antarctic summer, a small bit of light gets to these depths and the organisms use that light for energy, giving off oxygen.

That tiny bit of oxygen enters the surrounding environment, but it isn’t enough to overwhelm the surrounding anoxic environment. In other words, these pods create a tiny oasis of oxygen around them. A similar environment could explain how oxygen first arrived in the oceans. Tiny bits of oxygen could have formed oases in the ocean over hundreds of millions of years, giving time for other organisms to adapt to the presence of free oxygen in the ocean before the Great Oxygenation Event.

-JBB

Image credit: Tyler Mackey http://bit.ly/1KuHBAl

Original paper: http://bit.ly/1ZRUYai

Photosynthesis Discovery May Pave the Way for Higher Crop Yields

We occasionally discuss on TES about how agricultural production negatively affects the environment. As the demand for food increases along with the global population, the importance of finding sustainable, economical, and environmentally friendly ways to achieve this becomes more elusive. However, researchers at the University of Edinburgh have brought us a step closer to making this a reality.

Scientists studied algae cells which are known to have a specific mechanism that boosts the internal concentration of carbon dioxide during photosynthesis. This mechanism can support other processes which convert carbon stores into the sugar cells a plant requires to grow. Most crops and vegetables photosynthesize in a less efficient manner, lacking the ability raise internal CO2 concentrations in the same way as algae.

During this research project, plant experts found that it was possible that the algae could be implanted in other types of cells to boost growth. This was then successfully tested by transferring components into cress and tobacco plants, where they located the correct places in the cells. The results were published in Plant Biotechnology Journal, in collaboration with the University of Cambridge, the John Innes Centre, and the Carnegie Institution for Science.

The University of Edinburgh’s Dr. Alistair McCormick, who led the research, stated: "Simple plants such as algae are very good at fixing carbon from the air, compared with complex plants such as rice and wheat. If we can harness the systems that simple plants use to grow efficiently, we may be able to create highly productive crops."

Since the 1950’s, nitrogen- and phosphorous-infused fertilizers have been used to increase crop yields the world over. While these fertilizers can improve crop yields, they negatively impact the surrounding environment in various ways, particularly underground aquifers and rivers. Discoveries such as this bring us closer to finding conciliation between the economy and the environment.

-GG

Sources: http://bit.ly/1STvelV http://bit.ly/1PUlB7e

Image: Dr. Alistair McCormick

A sure sign of the onset of autumn can be seen in the leaves of trees. During the spring and summer the leaves have served as factories where most of the foods necessary for the tree's growth are manufactured. The process, known as photosynthesis, takes place in the leaf in numerous cells containing chlorophyll a and b. Chlorophyll a molecules absorb light at a wavelength of 400-500nm, while chlorophyll b absorbs light in the 550-700nm as a result, the green spectrum is reflected and this is what we see.

However, along with the green pigment are yellow to orange pigments; carotenes and xanthophyll, however most of the year these colours are masked by great amounts of chlorophyll.

In autumn, because of the changes in daylight hours and changes in temperature, the leaves stop photosynthesising and hence the chlorophyll breaks down. The green colour disappears, and the yellow and orange colours become visible. At the same time other chemical changes may occur, which form additional colours through the development of red anthocyanin pigments and as a result, beautiful landscapes.

-Jean

Photos by:

Top left: Diana Rudick http://www.boston.com/bigpicture/2009/10/autumn_scenes.html

Top right: Levi Basist http://gizmodo.com/40-stunning-photos-of-fall-foliage-1463053579

Bottom left:Patrick Pleul http://www.nbcnews.com/slideshow/today/fall-splendor-39689115

Bottom right: Agustin Rafael Reyes https://500px.com/arcreyes

What is acid mine drainage?

A couple weeks ago, the US Environmental Protection Agency accidentally ruptured a wall at an abandoned gold mine in Colorado, releasing a pulse of acid mine drainage pollution into the nearby Animas River.

We covered this spill when it originally happened in this post: http://tmblr.co/Zyv2Js1rYLYZc. Now that the flood of pollution has traveled downstream, we can go through more of the actual science behind what happened in this spill. The first step in understanding spills like this one is to understand what acid mine drainage is and how it turned a river the color of “Tang mixed with turmeric”, which was the best description I heard.

Our story begins, like many on Earth, 4.56 billion years ago. When the Earth formed, its atmosphere was chemically in equilibrium with the rocks in the mantle. Oxygen is the most abundant element in the mantle, but all that oxygen is taken up bonding with elements like silicon, magnesium, and iron. There was so much of these elements that there was no oxygen left in the atmosphere – the planet’s atmosphere started off reducing, filled with gases like methane that would burn in today’s atmosphere.

2.5 billion years ago, the atmosphere changed. Oxygen built up in the atmosphere after life developed photosynthesis, but this oxygen didn’t reach the mantle. Today, the inside of the planet is out of equilibrium with the atmosphere; rocks from the mantle brought to the surface will chemically react with the atmosphere, giving off energy.

An atmosphere and a planet out of equilibrium with each other is what drives acid mine drainage. Rocks that contain ores like gold and silver are formed out of the mantle, distilled and concentrated by magmatic processes. However, they’re still in the ground, still in equilibrium with the mantle.

When those rocks are exposed to the surface, they begin to chemically react. One of the most reactive elements in mantle rocks is iron. It’s extremely common in the mantle and as anyone who has seen a piece of rusted metal can tell you, when it is exposed at the surface it iron will chemically react with the atmosphere to form rust.

In rocks such as those of the Colorado Mineral Belt much of the iron is contained within the mineral pyrite, which is commonly known as fools gold. The chemical formula of Pyrite is FeS2, so it has iron in the structure. That mineral is extremely common on Earth; it’s found in all sorts of ore bodies, coal layers, and other rocks that are mined. Pyrite is stable when surrounded by other rocks in the crust, but when it is exposed to oxygen and water, it starts to react.

In other words, when we bring pyrite up to the surface, we cause it to react. It’s happy when its buried, but pyrite plus oxygen causes a chemical reaction.

This reaction uses oxygen and releases sulfuric acid. In the process, it oxidizes the iron – basically the iron rusts. Rusted iron does not dissolve easily in water; instead it precipitates to form tiny grains of solid minerals. These mineral grains can be carried downstream by the water in suspension or settle out onto the bottom of rivers, coating rocks and plants in the process. These minerals are commonly termed “Yellow boy” and they are the source of the mustard color seen in the Animas River after this spill.

Although the iron is the most easily recognized product of acid mine drainage due to its distinct color, it’s not the worst part of this chemical brew. Iron can kill life in streams by coating it and eliminating plants or food sources, but it doesn’t easily poison life. Instead, it’s the other parts of acid mine drainage that are the real worry.

Pyrite reacts more easily with acidic water, so the acid generated by pyrite weathering makes the pyrite weather even faster. Acid mine drainage is a runaway process that can make water extremely acidic; pH values as low as -3.6 (that’s a pH of negative 3) have been measured in a California mine (although the pH meter doesn't respond well when the pH gets below 0.5).

Extremely acidic water can dissolve all sorts of other nasty compounds. Some compounds like arsenic can be contained within the pyrite, others can be contained within the surrounding rocks, but when they touch highly acidic water they dissolve easily. These other compounds are extremely worrisome as they can harm humans if they are concentrated enough.

The exact chemistry of the water depends on the chemistry of the exposed rocks, but huge amounts of metal can dissolve in waters this acidic. Arsenic, copper, zinc, cadmium, nickel, lead, uranium, and so on can be found in these waters. Obviously people won’t directly drink mustard-colored water, but the dissolved compounds can leak into groundwater and contaminate large areas where the color isn’t obvious.

Acid mine drainage is a huge problem worldwide. Pyrite is extremely common, found in igneous, metamorphic, and sedimentary settings, and it is directly associated with many rock types that humans want to use. There are tens of thousands of mines in the U.S. that expose pyrite at the surface in the mine waste. They are a legacy of centuries of mining worldwide.

There’s a very good chance that right now there are mines leaking acidic water into the streams that feed whatever water system you use. Most water treatment systems are designed to take those pollutants out of the water and those compounds are diluted by water from fresher streams before they reach you, but it is a serious problem worldwide and it costs a lot of money to treat. The breach of this one mine in Colorado is just one case of it being released suddenly, but this waste is leaking in thousands of places around the world right now.

-JBB

Image credit: Environmental Protection Agency http://www.livescience.com/51820-colorado-mine-spill-river-photos.html

References http://water.usgs.gov/edu/mining-waterquality.html http://minerals.cr.usgs.gov/gips/na/drain.html http://digitalcommons.unl.edu/usgsstaffpub/479/

Coralline landscapes

Corals are a symbiosis (an ecological relationship in which two or more species cooperate and live together to their mutual benefit) between polyps and algae. The polyps build the structures and hunt microorganisms, providing a home for the algae that contribute energy via photosynthesis. The resulting landscapes in macro are simply amazing. Sadly corals all over the world are under threat from human activities such as fishing, ocean warming due to climate change and increased acidification of the seawater due to the rise in dissolved CO2, and a major bleaching event is now under way worldwide (see http://on.fb.me/1EhnfaO).

Loz

Image credit: Silvie de Burie

Check out our blog for some great video of coral feeding: http://tmblr.co/Zyv2Js1qYyzIQ