Evolution Archives

June 2, 2012December 23, 2015 by Jason Major

When Everything On Earth Died

Based on fossil records, 250 million years ago over 90% of all species on Earth died out, effectively resetting evolution. (Image: Lunar and Planetary Institute)

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Hey, remember that one time when 90% of all life on Earth got wiped out?

I don’t either. But it’s a good thing it happened because otherwise none of us would be here to… not remember it. Still, the end-Permian Extinction — a.k.a. the Great Dying — was very much a real crisis for life on Earth 252 million years ago. It makes the K-T extinction event of the dinosaurs look like a rather nice day by comparison, and is literally the most catastrophic event known to have ever befallen Earthly life. Luckily for us (and pretty much all of the species that have arisen since) the situation eventually sorted itself out. But how long did that take?

Screen Shot 2012-05-29 at 9.14.05 PM — An alien Earth: what our planet looked like during the time of the Permian Extinction. (Via The Planetary Habitability Laboratory @ UPR Arecibo, NASA, Ron Blakey and Colorado Plateau Geosystems, Inc., and The PaleoMap Project)

The Permian Extinction was a perfect storm of geological events that resulted in the disappearance of over 90% of life on Earth — both on land and in the oceans. (Or ocean, as I should say, since at that time the land mass of Earth had gathered into one enormous continent — called Pangaea — and thus there was one ocean, referred to as Panthalassa.) A combination of increased volcanism, global warming, acid rain, ocean acidification and anoxia, and the loss of shallow sea habitats (due to the single large continent) set up a series of extinctions that nearly wiped our planet’s biological slate clean.

Exactly why the event occurred and how Earth returned to a state in which live could once again thrive is still debated by scientists, but it’s now been estimated that the recovery process took about 10 million years.

(Read: Recovering From a Mass Extinction is Slow Going)

Research by Dr. Zhong-Qiang Chen from the China University of Geosciences in Wuhan, and Professor Michael Benton from the University of Bristol, UK, show that repeated setbacks in conditions on Earth continued for 5 to 6 million years after the initial wave of extinctions. It appears that every time life would begin to recover within an ecological niche, another wave of environmental calamities would break.

“Life seemed to be getting back to normal when another crisis hit and set it back again,” said Prof. Benton. “The carbon crises were repeated many times, and then finally conditions became normal again after five million years or so.”

“The causes of the killing – global warming, acid rain, ocean acidification – sound eerily familiar to us today. Perhaps we can learn something from these ancient events.”

– Michael Benton, Professor of Vertebrate Palaeontology at the University of Bristol

It wasn’t until the severity of the crises abated that life could gradually begin reclaiming and rebuilding Earth’s ecosystems. New forms of life appeared, taking advantage of open niches to grab a foothold in a new world. It was then that many of the ecosystems we see today made their start, and opened the door for the rise of Earth’s most famous prehistoric critters: the dinosaurs.

“The event had re-set evolution,” said Benton. “However, the causes of the killing – global warming, acid rain, ocean acidification – sound eerily familiar to us today. Perhaps we can learn something from these ancient events.”

The team’s research was published in the May 27 issue of Nature Geoscience. Read more on the University of Bristol’s website here.

March 30, 2012December 23, 2015 by Jason Major

Shaking Up Theories Of Earth’s Formation

Earth may not have formed quite like once thought (Image: NASA/Suomi NPP)

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Researchers from The Australian National University are suggesting that Earth didn’t form as previously thought, shaking up some long-standing hypotheses of our planet’s origins right down to the core — literally.

Ian Campbell and Hugh O’Neill, both professors at ANU’s Research School for Earth Sciences, have challenged the concept that Earth formed from the same material as the Sun — and thus has a “chondritic” composition — an idea that has been assumed accurate by planetary scientists for quite some time.

chondrule_lm — Chondrite meteorites are composed of spherical chondrules, which formed in the solar nebula before the asteroids. (NASA)

Chondrites are meteorites that were formed from the solar nebula that surrounded the Sun over 4.6 billion years ago. They are valuable to scientists because of their direct relationship with the early Solar System and the primordial material they contain.

“For decades it has been assumed that the Earth had the same composition as the Sun, as long the most volatile elements like hydrogen are excluded,” O’Neill said. “This theory is based on the idea that everything in the solar system in general has the same composition. Since the Sun comprises 99 per cent of the solar system, this composition is essentially that of the Sun.”

Instead, they propose that our planet was formed through the collision of larger planet-sized bodies, bodies that had already grown massive enough themselves to develop an outer shell.

This scenario is supported by over 20 years of research by Campbell on columns of hot rock that rise from Earth’s core, called mantle plumes. Campbell discovered no evidence for “hidden reservoirs” of heat-producing elements such as uranium and thorium that had been assumed to exist, had Earth actually formed from chondritic material.

“Mantle plumes simply don’t release enough heat for these reservoirs to exist. As a consequence the Earth simply does not have the same composition as chondrites or the Sun,” Campbell said.

The outer shell of early Earth, containing heat-producing elements obtained from the impacting smaller planets, would have been eroded away by all the collisions.

“This produced an Earth that has fewer heat producing elements than chondritic meteorites, which explains why the Earth doesn’t have the same chemical composition,” O’Neill said.

The team’s paper has been published in the journal Nature. Read the press release from The Australian National University here.

February 3, 2012December 24, 2015 by Paul Scott Anderson

How Plants May Have Helped Create Earth’s Unique Landscapes

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According to conventional thinking, plant life first took hold on Earth after oceans and rivers formed; the soil produced by liquid water breaking down bare rock provided an ideal medium for plants to grow in. It certainly sounds logical, but a new study is challenging that view – the theory is that vascular plants, those containing a transport system for water and nutrients, actually created a cycle of glaciation and melting, conditions which led to the formation of rivers and mud which allowed forests and farmland to later develop. In short, they helped actually create the landscapes we see today.

The evidence was just published in two articles in a special edition of Nature Geoscience.

In the first article, analysis of the data proposes that vascular plants began to absorb the carbon dioxide in the atmosphere about 450 million years ago. This led to a cooling of temperatures on a global scale, resulting in widespread glaciation. As the glaciers later started to melt, they ground up the Earth’s surface, forming the kind of soils we see today.

The second article goes further, stating that today’s rivers were also created by vascular plants – the vegetation broke the rocks down into mud and minerals and then also held the mud in place. This caused river banks to start forming, acting as channels for water, which up until then had tended to flow over the surface much more randomly. As the water was channeled into more specific routes, rivers formed. This led to periodic flooding; sediments were deposited over large areas which created rich soil. As trees were able to take root in this new soil, debris from the trees fell into the rivers, creating logjams. This had the effect of creating new rivers and causing more flooding. These larger fertile areas were then able to support the growth of larger lush forests and farmland.

According to Martin Gibling, a professor of Earth science at Dalhousie University, “Sedimentary rocks, before plants, contained almost no mud. But after plants developed, the mud content increased dramatically. Muddy landscapes expanded greatly. A new kind of eco-space was created that wasn’t there before.”

The new theory also leads to the possibility that any exoplanets that happen to have vegetation would look different from Earth; varying circumstances would create a surface unique to each world. Any truly Earth-like exoplanets might be very similar in general, but the way that their surfaces have been modified might be rather different.

It’s an interesting scenario, but it also raises other questions. What about the ancient river channels on Mars? Some appear to have been formed by brief catastrophic floods, but others seem more similar to long-lived rivers here on Earth, especially if there actually was a northern hemisphere ocean as well. How did they form? Does this mean that rivers could form in a variety of ways, with or without plant life being involved? Could Mars have once had something equivalent to vascular plant life as well? Or could the new theory just be wrong? Then there’s Titan, which has numerous rivers still flowing today. Albeit they are liquid methane/ethane instead of water, but what exactly led to their formation?

From the editorial in Nature Geoscience:

Without the workings of life, the Earth would not be the planet it is today. Even if there are a number of planets that could support tectonics, running water and the chemical cycles that are essential for life as we know it, it seems unlikely that any of them would look like Earth. Even if evolution follows a predictable path, filling all available niches in a reproducible and consistent way, the niches on any Earth analogue could be different if the composition of its surface and atmosphere are not identical to those of Earth. And if evolution is random, the differences would be expected to be even larger. Either way, a glimpse of the surface of an exoplanet — if we ever get one — may give us a whole new perspective on biogeochemical cycling and geomorphology.

Just as the many exoplanets now being found are of a previously unknown and amazingly wide variety, and all uniquely alien, even the ones that (may) support life are likely to be just as diverse from each other as they are from Earth itself. Earth’s “twin” may be out there, but in terms of outward appearance, it may be somewhat more of a fraternal twin than an exact replica.

January 23, 2012December 24, 2015 by Paul Scott Anderson

Key Step in Evolution Replicated by Scientists – With Yeast

Sacharomyces cerevisiae yeast cells. Credit: Wikimedia Commons

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One of the great puzzles in science has been the evolution of single-celled organisms into the incredibly wide variety of flora and fauna that we see today. How did Earth make the transition from an initially lifeless ball of rock to one populated only by single-celled organisms to a world teeming with more complex life?

As scientists understand it, single-celled organisms first began evolving into more complex forms more than 500 million years ago, as they began to form multi-cellular clusters. What isn’t understood is just how that process happened. But now, biologists are another step closer figuring out this puzzle, by successfully replicating this key step – using an ingredient common in the making of bread and beer – ordinary Brewer’s yeast (Saccharomyces cerevisiae). While helping to solve evolutionary riddles here on Earth, it also by extension has bearing on the question of biological evolution on other planets or moons as well.

The results were published in last week’s issue of the Journal Proceedings of the National Academy of Sciences (PNAS).

Yeasts are a microscopic form of fungi; they are uni-cellular but can become multi-cellular through the formation of a string of connected budding cells, like in molds. The experiments were based on this fact, and were surprisingly simple, they just hadn’t been done before, according to Will Ratcliff, a scientist at the University of Minnesota (UMN) and a co-author of the paper. “I don’t think anyone had ever tried it before,” he said, adding: “There aren’t many scientists doing experimental evolution, and they’re trying to answer questions about evolution, not recreate it.”

Sam Scheiner, program director in NSF’s Division of Environmental Biology, also adds: “To understand why the world is full of plants and animals, including humans, we need to know how one-celled organisms made the switch to living as a group, as multi-celled organisms. This study is the first to experimentally observe that transition, providing a look at an event that took place hundreds of millions of years ago.”

It’s been thought that the step toward multi-cellular complexity was a difficult one, an evolutionary hurdle that would be very hard to overcome. The new research however, suggests it may not be that difficult after all.

It took the first experiment only 60 days to produce results. The yeast was first added to a nutrient-rich culture, then the cells were allowed to grow for one day. They were then stratified by weight using a centrifuge. Clusters of yeast cells landed on the bottom of the test tubes. The process was then repeated, taking the cell clusters and re-adding them to fresh cultures. After sixty cycles of this, the cell clusters started to look like spherical snowflakes, composed of hundreds of cells.

The most significant finding was that the cells were not just clustering and sticking together randomly; the clusters were composed of cells that were genetically related to each other and remained attached after cell division. When clusters reached “critical mass,” some cells died, a process known as apoptosis, which allows the offspring to separate.

This then, simply put, is the process toward multi-cellular life. As described by Ratcliff, “A cluster alone isn’t multi-cellular. But when cells in a cluster cooperate, make sacrifices for the common good, and adapt to change, that’s an evolutionary transition to multi-cellularity.”

So next time you are baking bread or brewing your own beer, consider the fact that those lowly little yeast cells hold a lot more importance than just a useful role in your kitchen – they are also helping to solve some of the biggest mysteries of how life started, both here and perhaps elsewhere.

June 21, 2011December 24, 2015 by Tammy Plotner

Sleeping Beauties: A Galactic Fairye Tale

Bluer galaxies are actively “awake” and forming stars, while redder galaxies have shut down and are “asleep.” (Image: NASA, ESA, S. Beckwith (STScI) and the HUDF team)

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It’s a well known fact that galaxies come in two types – either actively forming stars or not. In simplistic terms, that means they are either awake or asleep. But now scientists are looking back twelve billion light years across time to find the same holds just as true then as it does now. As a matter of fact, galaxies may have been behaving this way for around 85% of the history of the Universe.

“The fact that we see such young galaxies in the distant universe that have already shut off is remarkable,” said Kate Whitaker, a Yale University graduate student and lead author of the paper, which is published in the June 20 online edition of the Astrophysical Journal.

So, without poking the sleeping dragon, just how did the astronomers make their determinations? Try with the use of a 4-meter Kitt Peak telescope in Arizona and a special set of filters developed by Whitaker and her team. Just like all astronomy filters, this new breed is selective to certain bandpasses, or wavelengths, of light. These new filter sets were then used on 40,000 galaxies over a 75 night period and the data collected and examined. The end product was the deepest and most comprehensive of its kind so far. Active, awake galaxies appear more blue, while the sleepy-heads appear red. Believe it or not, when it comes to the cosmic bedroom there’s more activity than previously thought.

“We don’t see many galaxies in the in-between state,” said Pieter van Dokkum, a Yale astronomer and another author of the paper. “This discovery shows how quickly galaxies go from one state to the other, from actively forming stars to shutting off.”

Whether the dozing galaxies have completely shut down remains an open question, Whitaker said. However, the new study suggests the active galaxies are forming stars at rates about 50 times greater than their somnambulistic counterparts. “Next, we hope to determine whether galaxies go back and forth between waking and sleeping or whether they fall asleep and never wake up again,” van Dokkum said. “We’re also interested in how long it takes galaxies to fall asleep, and whether we can catch one in the act of dozing off.”

Pass the Red Bull… and sing the blues! “Are you sleeping? Can you hear me? Do you know if I am by your side? Does it matter? If you hear me? When the mornin’ comes I’ll be there by your side… There was a time, we had a time. There was a time we had time…”

Original Story Source: Yale Daily Bulletin.

June 21, 2011December 24, 2015 by Tammy Plotner

The ATLAS3D Project: Calling A Different Tune

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In 1926, astronomer Edwin Hubble gave us our first basic galaxy classification scenario – the Hubble Sequence. Using photographic plates, Hubble derived a simplistic system based on three visually known structures: elipitical, spiral and lenticular. This sequence, when plotted out, gave the appearance of a common object and eventually became known as the “Hubble Tuning Fork” (as seen above). For many decades, this served as a standard. Now the ATLAS3D Project is calling a different tune…

Just who is the pied piper in this merry band? The ATLAS3D project is a multiwavelength survey combined with a theoretical modelling effort. The observations it takes spans from the radio to the millimetre and optical. It provides multicolor imaging, as well as two-dimensional kinematics of the atomic, molecular and ionized gases, together with the kinematics and population of the stars, Where does it dance? Only around a carefully selected, volume-limited sample of 260 early-type galaxies.

Heading up the project is a team of 25 astronomers from Europe and Northern America, including ASTRON astronomers Morganti, Oosterloo, and Serra – and all with a mission – to update and revise our understanding of galactic evolution. Employing the SAURON spectrograph on the 4.2-meter William Herschel Telescope on La Palma, the team was able to distinguish stellar movement in the pre-determined galactic candidates. These new assessments show that spheroid galaxies belong to the spiral galaxy classification. How did they come to that conclusion? The largest portion of spheroids – or early types – are basically the same family as spirals and evolve along a similar line. But with ATLAS3D findings, we’re looking at new concepts.

We’re seeing beyond the optical (photographic plates) which founded Hubble’s original diagram – where once galaxies were separated by their distinct characteristics such as rapid rotators rich in stars and gas – or as slowly moving, gas-poor models. Up until now, it was also next to impossible to distinguish sparse “face-on” structure from edge-on spheroids. With the aid of kinematic data astronomers can “see” rotation – allowing observation of all galaxy types from any angle.

“Slow and fast rotators tend to be classified as ellipticals and lenticulars, respectively, but the contamination is strong enough to affect results solely based on such a scheme: 20 per cent of all fast rotators are classified as ellipticals, and more importantly 66 per cent of all ellipticals in the ATLAS3D sample are fast rotators.” says the team. “Our complete sample of 260 ETGs leads to a new criterion to disentangle fast and slow rotators which now includes a dependency on the apparent ellipticity. It separates the two classes significantly better than the previous prescription.”

While it will take many years and many more observations to sort out all the new data, it would seem that our current understanding of galactic evolution just might need a “tune up”.

Oringinal Story Source: ASTRON.

March 17, 2011April 26, 2016 by Jon Voisey

The Universe Verse Continues – It’s Alive!

Back in 2009, I was given an odd book. It was the Universe Verse: Book One. In it, the author illustrates the formation of the universe, from the Big Bang, to the formation of stars and galaxies in rich detail and painstaking attention to the tiniest of scientific facts. And to top it off, it’s all done in rhyme as if Carl Sagan met Dr. Seuss. But as the title indicates, it was just the first of the series. In total, the author, James Lu Dunbar, is planning three books and at long last, the second in the Universe Verse trilogy is ready for release. And we’ve got a sneak peek!

The previous book (available to preview on the author’s website) ended with the formation of heavy atoms in the cores of stars and supernovae. “It’s Alive!” begins with the formation of planets from these elements. It explains the formation of primordial oceans and the atmosphere and introduces abiogenesis. It takes the reader through the fundamentals of random mutations leading to natural selection, formation of amino acids, and biodiversity.

This chapter in the saga leaves off with life still quite simple, still at the bacterial level, but with hints at what it will become (the province of the next book). As with the previous book, this one is lavishly illustrated, but unlike its predecessor, it’s in color. This was all thanks to a series of pledges James received to continue his project, netting him six times more than the amount requested!

Like the last book, this one can be previewed free online, but to go even further, James is releasing the book as a free eBook. All you have to do is send him an Email (address on his website) for a high resolution .pdf copy! He encourages anyone interested to request it since “Everyone, especially children, should have the opportunity to read this story.” For even more behind the scenes with this book, James chronicled the making of the book, complete with rough draft pages on his blog.

For those interested in purchasing the book, it will available for purchase in paperback on April 3rd of this year. Preorders are available here.

December 14, 2010December 24, 2015 by Jon Voisey

Darwin vs. the Sun

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Today, we take it for granted that the Sun produces energy via nuclear fusion. However, this realization only came about in the early 1900’s and wasn’t confirmed until several decades later (see the Solar Neutrino Problem). Prior to that, several other methods of energy production had been proposed. These ranged from burning coal to a constant bombardment of comets and meteors to slow contraction. Each of these methods seemed initially plausible, but when astronomers of the time worked out how long each one could sustain such a brightness, they came up against an unlikely opponent: Charles Darwin.

In a “Catholic Magazine and Review” from 1889, known as The Month, there is a good record of the development of the problem faced in an article titled “The Age of the Sun and Darwinism”. It begins with a review of the recently discovered Law of Conservation of Energy in which they establish that a method of generation must be established and that this question is necessarily entangled with the age of the Sun and also, life on Earth. Without a constant generation of energy, the Sun would quickly cool and this was known to be unlikely due to archaeological evidences which hinted that the Sun’s output had been constant for at least 4,000 years.

While burning coal seemed a good candidate since coal power was just coming into fashion at the time, scientists had calculated that even burning in pure oxygen, the Sun could only last ~6,000 years. The article feared that this may signal “the end of supplies of heat and light to our globe would be very near indeed” since religious scholars held the age of the Earth to be some “4000 years of chronological time before the Christian era, and 1800 since”.

The bombardment hypothesis was also examined explaining that the transference of kinetic energy can increase temperatures citing examples of bullets striking metal surfaces or hammers heating anvils. But again, calculations hinted that this too was wrong. The rate with which the Sun would have to accumulate mass was extremely high. So much so that it would lead to the “derangement of the whole mechanism of the heavens.” The result would be that the period of the year over the past ~6,000 years would have shortened by six weeks and that the Earth too would be constantly bombarded by meteors (although some especially strong meteor showers at that time lent some credence to this).

The only strong candidate left was that of gravitational contraction proposed by Sir William Thomson (later Lord Kelvin) and Hermann von Helmholtz in a series of papers they began publishing in 1854. But in 1859, Darwin published the Origin of Species in which he required an age of at least two billion years. Thomson’s and Helmholtz’s hypothesis could only support an age of some tens of millions of years. Thus astronomy and biology were brought head to head. Darwin was fully aware of this problem. In a letter to a friend, he wrote that, “Thomson’s views of the recent age of the world have been for some time one of my sorest troubles”.

To back the astronomers was the developing field of spectroscopy in which they determined that the sun and other stars bared a strong similarity to that of nebulae. These nebulae could contract under their own gravity and as such, provided a natural establishment for the formation of stars, leading gracefully into the contraction hypothesis. Although not mentioned in the article, Darwin did have some support from geologists like Charles Lyell who studied the formation of mountain ranges and also posited an older Earth.

Some astronomers attempted to add other methods in addition to gravitational contraction (such as tidal friction) to extend the age of the solar system, but none could reach the age required by Darwin. Similarly, some biologists worked to speed up evolutionary processes by positing separate events of abiogenesis to shave off some of the required time for diversification of various kingdoms. But these too could not rectify the problem.

Ultimately, the article throws its weight in the camp of the doomed astronomers. Interestingly, much of the same rhetoric in use by anti-evolutionists today can be found in the article. They state, “it is not surprising to find men of science, who not only have not the slightest doubt about the truth of their own pet theories, but are ready to lay down the law in the realms of philosophy and theology, in science which with, to judge from their immoderate assertions, their acquaintance is of the most remote? Such language is to be expected from the camp-followers in the army of science, who assurance is generally inversely proportional to their knowledge, for many of those in a word who affect to popularize the doctrine of Natural Selection.”

In time, Darwin would win the battle as astronomers would realize that gravitational contraction was just the match that lit the fuse of fusion. However, we must ask whether scientists would have been as quickly able to accept the proposition of stellar fusion had Darwin not pointed out the fundamental contradiction in ages?

November 13, 2010December 24, 2015 by Steve Nerlich

Astronomy Without A Telescope – Necropanspermia

Exogenesis — A new instrument called the Search for Extra-Terrestrial Genomes (STEG) is being developed to find evidence of life on other worlds. Credit: NASA/Jenny Mottor

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The idea that a tiny organism could hitchhike aboard a mote of space dust and cross vast stretches of space and time until it landed and took up residence on the early Earth does seem a bit implausible. More likely any such organisms would have been long dead by the time they reached Earth. But… might those long dead alien carcasses still have provided the genomic template that kick started life on Earth? Welcome to necropanspermia.

Panspermia, the theory that life originated somewhere else in the universe and was then transported to Earth requires some consideration of where that somewhere else might be. As far as the solar system is concerned – the most likely candidate site for the spontaneous formation of a water-solvent carbon-based replicator is… well, Earth. And, since all the planets are of a similar age, the only obvious reason to appeal to the notion that life must have spontaneously formed somewhere else, is if a much longer time span than was available in the early solar system is required.

Opinions vary, but Earth may have offered a reasonably stable and watery environment from about 4.3 billion years until 3.8 billion years ago – which is about when the first evidence of life becomes apparent in the fossil record. This represents a good half billion years for some kind of primitive chemical replicator to evolve into a self-contained microorganism capable of metabolic energy production and capable of building another self-contained microorganism.

Half a billion years sounds like a generous amount of time – although with only one example to go by, who knows what a generous amount of time really is. Wesson (below) argues that it is not enough time – referring to other researchers who calculate that random molecular interactions over half a billion years would only produce about 194 bits of information – while a typical virus genome carries 120,000 bits – and an E. coli bacterial genome carries about 6 million bits.

A counter argument to this is that any level of replication in a environment with limited raw materials favors those entities that are most efficient at replication – and continues to do so generation after generation – which means it very quickly ceases to be an environment of random molecular interactions.

Put the term panspermia in a search engineand you get (left) ALH84001, a meteorite from Mars which has some funny looking structures which may just be mineral deposits; and (right) a tardigrade - a totally terrestrial organism that can endure high levels of radiation, desiccation and near vacuum conditions - although it much prefers to live in wet moss. Credit: NASA

The mechanism through which a dead alien genome usefully became the information template for further organic replication on Earth is not described in detail and the case for necropanspermia is not immediately compelling.

The theory still requires that the early Earth was ideally primed and ripe for seeding – with a gently warmed cocktail of organic compounds, shaken-but-not-stirred, beneath a protective atmosphere and a magnetosphere. Under these circumstances, the establishment of a primeval replicator through a fortuitous conjunction of organic compounds remains quite plausible. It is not clear that we need to appeal to the arrival of a dead interstellar virus to kick start the world as we know it.

Further reading: Wesson, P. Panspermia, past and present: Astrophysical and Biophysical Conditions for the Dissemination of Life in Space.

April 9, 2009December 24, 2015 by Anne Minard

Without Nickel, Life on Earth Could Finally Breathe

Caption: Banded iron formations like this from northern Michigan contain evidence of a drop in dissolved nickel in ancient oceans. Credit: Carnegie Institution for Science

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Researchers have long puzzled over why oxygen flourished in Earth’s atmosphere starting around 2.4 billion years.

Called the “Great Oxidation Event,” the transition “irreversibly changed surface environments on Earth and ultimately made advanced life possible,” said Dominic Papineau of the Carnegie Institution’s Geophysical Laboratory.

Now, Papineau has co-authored a new study in the journal Nature, which reveals new clues to the mystery in ancient sedimentary rocks.

The research team, led by Kurt Konhauser of the University of Alberta in Edmonton, analyzed the trace element composition of sedimentary rocks known as banded-iron formations, or BIFs, from dozens of different localities around the world, ranging in age from 3,800 to 550 million years. Banded iron formations are unique, water-laid deposits often found in extremely old rock strata that formed before the atmosphere or oceans contained abundant oxygen. As their name implies, they are made of alternating bands of iron and silicate minerals.

They also contain minor amounts of nickel and other trace elements. And the history of nickel, the researchers think, may reveal a secret to the origin of modern life.

Nickel exists in today’s oceans in trace amounts, but was up to 400 times more abundant in the Earth’s primordial oceans. Methane-producing microorganisms, called methanogens, thrive in such environments, and the methane they released to the atmosphere might have prevented the buildup of oxygen gas, which would have reacted with the methane to produce carbon dioxide and water.

A drop in nickel concentration would have led to a “nickel famine” for the methanogens, who rely on nickel-based enzymes for key metabolic processes. Algae and other organisms that release oxygen during photosynthesis use different enzymes, and so would have been less affected by the nickel famine. As a result, atmospheric methane would have declined, and the conditions for the rise of oxygen would have been set in place.

The researchers found that nickel levels in the BIFs began dropping around 2.7 billion years ago and by 2.5 billion years ago was about half its earlier value.

“The timing fits very well. The drop in nickel could have set the stage for the Great Oxidation Event,” Papineau said. “And from what we know about living methanogens, lower levels of nickel would have severely cut back methane production.”

As for why nickel dropped in the first place, the researchers point to geology. During earlier phases of the Earth’s history, while its mantle was extremely hot, lavas from volcanic eruptions would have been relatively high in nickel. Erosion would have washed the nickel into the sea, keeping levels high. But as the mantle cooled, and the chemistry of lavas changed, volcanoes spewed out less nickel, and less would have found its way to the sea.

“The nickel connection was not something anyone had considered before,” Papineau said. “It’s just a trace element in seawater, but our study indicates that it may have had a huge impact on the Earth’s environment and on the history of life.”

Source: Carnegie Institution for Science, via Eurekalert.