Mind the gap

In 1869, explorer John Wesley Powell did the first systematic study of the geology of the Grand Canyon.  As impressive as it is, the Grand Canyon's not that complicated geologically; it's made of layers of sedimentary rock, most of them relatively undeformed, one on top of the other from the oldest at the bottom to the newest at the top.  A layer cake of billions of years of Earth history, and a wonderful example of the principle of superposition -- that strata form from the bottom up.

However, Powell also noted something rather peculiar.  It's called the Great Unconformity.  In geologic parlance, an unconformity is a break in the rock record, where the layer below is separated from the layer above by a gap in time when either no rocks were deposited (in that location, at least), or the rocks that were laid down were later removed by some natural process.  At that stage in the science, Powell didn't know when exactly the Great Unconformity occurred, but it was obvious that it was huge.  Something had taken away almost a billion years' worth of rocks -- and, it was later found out, that same chunk of rock was missing not only at the future site of the Grand Canyon, but across most of North America.

It was an open question as to why this happened, but one leading hypothesis was that it was massive glaciation.  Glaciers are extraordinarily good at breaking up rocks and moving them around, as I find out every time I dig in my garden and my shovel runs into the remnants of the late Pleistocene continental glaciation.  At that point, where my house is would have been under about thirty meters of ice; the southern extent is the Elmira moraine, a line of low hills fifty kilometers south of here, left behind when the glaciers, pushing piles of crushed rock and soil ahead of them like a backhoe, began to melt back and left all that debris for us gardeners to contend with ten thousand years later.

There was a time in which the Earth was -- as far as we can tell -- completely covered by ice. The Cryogenian Period, during the late Precambrian, is sometimes nicknamed the "Snowball Earth" -- and the thawing might have been one contributing factor to the development of complex animal life, an event called the "Cambrian explosion," about which I've written before.

The problem was, the better the data got, the more implausible this sounded as the cause of the Great Unconformity.  The rocks missing in the Great Unconformity seem to have preceded the beginning of the Cryogenian Period by a good three hundred million years.  And while there were probably earlier periods of worldwide glaciation -- perhaps several of them -- the fact that the Cryogenian came and went and didn't leave a second unconformity above the first led scientists away from this as an explanation.

However, a paper in Proceedings of the National Academy of Sciences, written by a team led by Francis Macdonald of the University of Colorado - Boulder, has come up with evidence supporting a different explanation.  Using samples of rock from Pike's Peak in Colorado, Macdonald's team used a clever technique called thermochronology to estimate how much rock had been removed.  Thermochronology uses the fact that some radioactive elements release helium-4 as a breakdown product, and helium (being a gas) diffuses out of the rock -- and the warmer it is, the faster it leaves.  So the amount of helium retained in the rock gives you a good idea of the temperature it experienced -- and thus, how deeply buried it was, as the temperature goes up the deeper down you dig.

What this told Macdonald's team is that the Pike's Peak granite, from right below the Great Unconformity, had once been buried under several kilometers of rock that then had been eroded away.  And from the timing of the removal -- on the order of a billion years ago -- it seems like what was responsible wasn't glaciation, but the formation of a supercontinent.

But not Pangaea, which is what most people think of when they hear "supercontinent."  Pangaea formed much later, something like 330 million years ago, and is probably one of the factors that contributed to the massive Permian-Triassic extinction.  This was two supercontinents earlier, specifically one called Rodinia.  What Macdonald's team proposes is that when Rodinia formed from prior separate plates colliding, this caused a huge amount of uplift, not only of the rocks of the continental chunks, but of the seafloor between them.  A similar process is what formed the Himalayas, as the Indian Plate collided with the Eurasian Plate -- and is why you can find marine fossils at the top of Mount Everest.

[Image is in the Public Domain]

When uplift occurs, erosion increases, as water and wind take those uplifted bits, grind them down, and attempt to return them to sea level.  And massive scale uplift results in a lot of rock being eroded.

Thus the missing layers in the Great Unconformity.

"These rocks have been buried and eroded multiple times through their history," study lead author Macdonald said, in an interview with Science Daily.  "These unconformities are forming again and again through tectonic processes.  What's really new is we can now access this much older history...  The basic hypothesis is that this large-scale erosion was driven by the formation and separation of supercontinents.  There are differences, and now we have the ability to perhaps resolve those differences and pull that record out."

What I find most amazing about this is how the subtle chemistry of rock layers can give us a lens into the conditions on the Earth a billion years ago.  Our capacity for discovery has expanded our view of the universe in ways that would have been unimaginable only thirty years ago.

And now, we have a theory that accounts for one of the great geological mysteries -- what happened to kilometer-thick layers of rock missing from sedimentary strata all over North America.

John Wesley Powell, I think, would have been thrilled.

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Thawing the snowball

One of the frightening things about a system in equilibrium is what happens when you perturb it.

Within limits, most systems can recover from perturbation through some combination of negative feedbacks.  An example is your body temperature.  If something makes it goes up -- exercise, for example, or being outside on a hot, humid day -- you sweat, bringing your temperature back down.  If your body temperature goes down too much, you increase your rate of burning calories, and also have responses like shivering -- which brings it back up.  Those combine to keep your temperature in a narrow range (what the biologists call homeostasis).

Push it too much, though, and the whole thing falls apart.  If your temperature rises beyond about 105 F, you can experience seizures, convulsions, brain damage -- or death.  Your feedback mechanisms are simply not able to cope.

This, in a nutshell, is why climate scientists are so concerned about the effects of anthropogenic carbon dioxide.  Within limits -- as with your body temperature -- an increase in carbon dioxide results in an increase in processes that remove the carbon dioxide from the atmosphere, and the whole system stays in equilibrium.  There is a tipping point, however.

The problem is that no one knows where it is -- and whether we may have already passed it.

A piece of research from the Virginia Polytechnic Institute, however, has suggested that this flip from stability to instability may be fast and unpredictable.  A paper authored by a team led by paleobiologist Shuhai Xiao, that was published in the journal Geology, looks at one of the main destabilization events that the Earth has ever experienced -- when the "Snowball Earth" thawed out in the late Precambrian Period, 635 million years ago.

Artist's conception of the Precambrian Snowball Earth [Image is in the Public Domain, courtesy of NASA/JPL]

Xiao and his team studied rocks from Yunnan and Guizhou, China, that are called cap carbonates.  They are made of limestone and dolomite and are deposited quickly in marine environments when the carbon dioxide content of the atmosphere spikes, leading to a dramatic temperature increase and a subsequent increase in absorption of carbonates into seawater (and ultimately deposition of those carbonates on the seafloor).  The cap carbonates Xiao et al. studied were dated to between 634.6 and 635.2 million years old, which means that the entire jump in both temperature and carbon dioxide content took less than 800,000 years.

So in less than a million years, the Earth went from being completely covered in ice to being subtropical.  The jump in global average temperature is estimated at 7 C -- conditions that then persisted for the next hundred million years.

Xiao et al. describe this as "the most severe paleoclimatic [event] in Earth history," and that the resulting deglaciations worldwide were "globally synchronous, rapid, and catastrophic."

Carol Dehler, a geologist at Utah State University, is unequivocal about the implications.  "I think one of the biggest messages that Snowball Earth can send humanity is that it shows the Earth’s capabilities to change in extreme ways on short and longer time scales."

What frustrates me most about today's climate change deniers is that they are entirely unwilling to admit that the changes we are seeing are happening at an unprecedented rate.  "It's all natural," they say.  "There have been climatic ups and downs throughout history."  Which is true -- as far as it goes.  But the speed with which the Earth is currently warming is faster than what the planet experienced when it flipped between an ice-covered frozen wasteland and a subtropical jungle.  It took 800,000 years to see an increase of the Earth's average temperature by 7 degrees C.

The best climate models predict that's what we'll see in two hundred years.

And that is why we're alarmed.

It's unknown what kind of effect that climate change in the Precambrian had on the existing life forms.  The fossil record just isn't that complete.  But whatever effect it had, the living creatures that were around when it happened had 800,000 years to adapt to the changing conditions.  What's certain is that an equivalent change in two centuries will cause massive extinctions.  Evolution simply doesn't happen that quickly.  Organisms that can't tolerate the temperature fluctuation will die.

We can only speculate on the effects this would have on humanity.

This is clearly the biggest threat we face, and yet the politicians still sit on their hands, claim it's not happening, that remediation would be too costly, that we can't prevent it, that short-term profits are more important than the long-term habitability of the Earth.  (Not to mention firing the people and closing the agencies that are currently trying to do something about it.)  Our descendants five hundred years from now will look upon the leaders from this century as having completely abdicated their responsibility of care for the people they represent.

Presuming we still have descendants at that point.

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Life inside the snowball

Right now, here in the wilds of upstate New York, it's cold, gray, and snowy.  They say our area has a "four-season climate" -- but usually neglect to add that the four seasons are Almost Winter, Winter, Still Fucking Winter, and Road Construction.

On the other hand, if you know something about prehistory, it could be a whole lot worse, and in fact, has been more than once.  The last continental glaciation in this part of the world, the Laurentide, resulted in an ice sheet that buried the spot where I'm now sitting under three hundred meters of ice, and dug out not only the nearby Finger Lakes but the Great Lakes.  The southern edge of the ice sheet created the Elmira Moraine, only thirty miles south of me -- a moraine is basically the debris left behind when a glacier recedes -- and also Long Island, the sand and gravel soils of which were shoved forward as the ice sheet pushed southward then left in place, much like the pile of snow left when a snowplow backs up (explaining its long, narrow shape).

So I shouldn't complain about the cold.  The era of the Laurentide Glaciation was a lot colder.  And in fact, there have been periods in Earth's history where everyone, not just people like who live in the frozen north, would have been in the icebox.

Our knowledge of this rather miserable time in the far distant past has, like so many discoveries, built by accretion.  In the 1870s and 1880s geologists found evidence of widespread glaciation in strata in Scotland -- then, more puzzlingly, in Australia and India.  Any deep understanding of this was hampered by the fact that back then, scientists thought the continents were firmly fixed in place; continental drift wasn't even first proposed until 1912, and then was soundly rejected until magnetometer data proved in 1958 that the tectonic plates were in constant motion.  The first evidence of a worldwide glaciation -- not just a big one, like the Laurentide -- was uncovered in 1964 by Cambridge University geologist W. Brian Harland, who showed that glacial strata in Svalbard and Greenland had been deposited in tropical latitudes.  Thus demonstrating two rather amazing conclusions in one fell swoop; first, that Svalbard and Greenland had moved a long way, and second, that at the time when they were near the equator, the whole world was covered with ice.

This "Snowball Earth" model has since been demonstrated as accurate in multiple ways.  More than once, but most significantly between 720 and 580 million years ago (i.e. the end of the Precambrian Era), the whole planet was covered with a kilometers-thick sheet of ice.  Picturing what this was like is a little mind-boggling.  The glaciers covered not only the land, but the entire ocean.  Because the liquid water underneath was moving, the ice sheets broke up and ground together, much like the rocky tectonic plates do today, floating on the liquid mantle of the Earth.  Any organisms caught in the cracks of the ice sheet, or between the glaciers and the seafloor, would have been pulverized.  "It’s basically like having a giant bulldozer," said Huw Griffiths, of the British Antarctic Survey, in an interview with Eos.  "The next glacial expansion would have just erased all [traces of life] and turned it into mush, basically."

Griffiths is the reason the topic comes up, actually; he, Rowan Whittle (also of the British Antarctic Survey), and Emily Mitchell (of the University of Cambridge) are the authors of a paper in The Journal of Geophysical Research that looked at the rare fossils that have survived since that time, and have drawn some fascinating parallels to species who survive today in similar conditions -- on the seafloor beneath the Antarctic Ice Sheets:

The timing of the first appearance of animals is of crucial importance for understanding the evolution of life on Earth.  Although the fossil record places the earliest metazoans at 572–602 Ma, molecular clock studies suggest a far earlier origination, as far back as ~850 Ma.  The difference in these dates would place the rise of animal life into a time period punctuated by multiple colossal, potentially global, glacial events...  The history of recent polar biota shows that organisms have found ways of persisting on and around the ice of the Antarctic continent throughout the Last Glacial Maximum (33–14 Ka), with some endemic species present before the breakup of Gondwana (180–23 Ma)...  [D]espite the apparent harshness of many ice covered, sub-zero, Antarctic marine habitats, animal life thrives on, in and under the ice.  Ice dominated systems and processes make some local environments more habitable through water circulation, oxygenation, terrigenous nutrient input and novel habitats...  The recent glacial cycle has driven the evolution of Antarctica's unique fauna by acting as a “diversity pump,” and the same could be true for the late Proterozoic and the evolution of animal life on Earth, and the existence of life elsewhere in the universe on icy worlds or moons.

One group of weird animals they looked at, which apparently thrived in these harsh conditions, were frondomorphs (Phylum Petalonamae), which are thought to have left no descendants whatsoever, and whose alliances to other animals are uncertain at best.

Fossil of a Precambrian frondomorph, Charniodiscus arboreus, from the Flinders Range in Australia [Image licensed under the Creative Commons tina negus from UK, Charniodiscus arboreus, CC BY 2.0]

These peculiar beasts were apparently anchored to the seafloor and absorbed nutrients and oxygen from the frigid waters through the feathery bits, but honestly, we know barely anything about how they made a living.  Some may have -- as many Antarctic sponges and sea anemones do today -- been affixed upside-down from the underside of the ice sheet.

These animals, nicknamed "extremophiles" for obvious reasons, just about all died out when things warmed up and the ice finally melted.  But it bears mentioning how long the Snowball Earth conditions persisted -- around 140 million years.  In other words, about the same amount of time as between the end of the Jurassic Period and now.   During that time, there were minor ups and downs, temperature-wise, but that's still a huge expanse of time during which the Earth was an ice-covered wasteland.

When the snowball finally did melt, and the cold-loving extremophiles such as Charniodiscus went extinct, it opened the door for one of the major events in the history of life on Earth -- the Cambrian explosion, when all of the main phyla of animals evolved in a relative flash.  But even when conditions were at their worst, life still survived, somehow.  The fact that life can thrive in apparently hostile conditions improves our chances of finding it elsewhere in the universe, and cheers me up significantly with regards to the weather we're currently having here.

It's also further support for the famous line from the inimitable Ian Malcolm in Jurassic Park: "Life, uh, finds a way."

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The geological time slip

The geologists have lost about a billion or so years, have you noticed?

This wee time slip has to do with the sedimentary strata best observed in the Grand Canyon, which showed a peculiarity noticed -- but not explained -- by explorer John Wesley Powell in 1869.  Powell knew about sedimentary rock formation and the Principle of Superposition -- the rather common-sensical idea that in undisturbed strata, the lower layers were formed first.  (It's like building a layer cake -- it'd be rather tricky to build it from the top down.)

In Powell's case, he noticed what looked like a jump in rock types and stratum structure, where because of fault lines and angles of tilt it seemed like there was a gap in the rock record.  What neither Powell nor anyone else knew at the time was how big this gap -- which Powell called "the Great Unconformity" -- was.

It represents the loss of about a billion years of accumulated rocks.

The Arroyo Penasco Formation showing the Great Unconformity, Montezuma, New Mexico [Image is in the Public Domain]

That by itself would be enough to suggest that whatever caused the Great Unconformity, it was not some local effect, and it didn't take much surveying to confirm this.  In fact, the same jump has been seen in just about every place there's rock of that age (right around the boundary between the Cambrian and Precambrian eras), most notably in the St. François Mountains of Arkansas and at Siccar Point on the east coast of Scotland.

In each case, there is 1.4 billion year old rock (mostly granite, rhyolite, and schist), and the layer immediately above it dates to around 500 million years ago.

In between -- nothing.

It wasn't until 1910 that the magnitude of this bizarre gap was fully appreciated.  In Cambrian Geology and Paleontology, geologist Charles D. Walcott wrote:

I do not know of a case of proven conformity between Cambrian and pre-Cambrian Algonkian rocks on the North American continent.  In all localities where the contact is sufficiently extensive, or where fossils have been found in the basal Cambrian beds or above the basal conglomerate and coarser sandstones, an unconformity has been found to exist.  Stated in another way, the pre-Cambrian land surface was formed of sedimentary, eruptive, and crystalline rocks that did not in any known instance immediately precede in deposition or origin the Cambrian sediments.  Everywhere there is a stratigraphic and time break between the known pre-Cambrian rocks and Cambrian sediments of the North American continent.

But what on Earth could tear down a billion years' worth of strata -- all over the world, more or less simultaneously (if you can call anything that had a duration of a billion years "simultaneous")?  Scientists believe that these missing layers represent something on the order of six to eight vertical kilometers of rock.

Some new research has indicated a possible trigger -- and perhaps the mechanism involved.  Back around the beginning of the gap, all of the continents of the Earth had slammed together to form one huge supercontinent.  This was pre-Pangaea, the one most people will think of; this was Rodinia, a colossal land mass that lasted from the late Precambrian Era to right about the beginning of the Cambrian, at which point rifting took over and the continents separated into a new configuration.

Here's what seems to have happened.  When Rodinia formed, the force of the collisions pushed a lot of rock skyward.  We're seeing exactly the same thing happen today in the Himalayas; Mount Everest is sedimentary rock that was once at the bottom of the ocean, but the collision between India and the main part of Asia scooped it up like a huge plow and raised enormous mountains.  This same process occurred during the formation of Rodinia, but on a global scale as all of the world's land masses collided.

But by the beginning of the Cambrian, a huge amount of that rock was gone, eroded away.  What could cause erosion on that scale?

It seems like the likeliest explanation is worldwide glaciation.  The late Precambrian has been called the "Cryogenic Period" -- from Greek words meaning "ice-forming" -- as well as the perhaps more vivid moniker of the "the Snowball Earth."  The shoving of the Precambrian rocks aloft created steep topography (again, just like in the Himalayas today), so any erosive forces, whether ice or liquid water, would have that much more gravity-driven force to grind it down.

As a biologist, what I find even cooler is that that breakup of Rodinia, which coincided with the thawing of the Snowball Earth, was also the beginning of a huge diversification of life on Earth, something that has been nicknamed the Cambrian Explosion.  I don't think it's a reach to hypothesize that these two events were connected.

So do we owe the current biodiversity -- and, by our extension, our own presence here -- to a process that erased every trace of a billion years of sedimentary rock layers?

I find it fascinating how everything is connected, and that even after a couple of centuries of intense study, there are still mysteries out there to solve.  The unconformities in our own knowledge are still huge, but unlike the one in the Grand Canyon, aren't immediately obvious.  Filling in these gaps inevitably opens up new questions, enough that scientists will never run out of new areas to explore.  As Socrates said, over two thousand years ago, "If I am accounted wise, it is only because I alone realize how little I know."

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One of the most enduring mysteries of neuroscience is the origin of consciousness.  We are aware of a "self," but where does that awareness come from, and what does it mean?  Does it arise out of purely biological processes -- or is it an indication of the presence of a "soul" or "spirit," with all of its implications about the potential for an afterlife and the independence of the mind and body?

Neuroscientist Anil Seth has taken a crack at this question of long standing in his new book Being You: A New Science of Consciousness, in which he brings a rigorous scientific approach to how we perceive the world around us, how we reconcile our internal and external worlds, and how we understand this mysterious "sense of self."  It's a fascinating look at how our brains make us who we are.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

Mind the gap

In 1869, explorer John Wesley Powell did the first systematic study of the geology of the Grand Canyon.  As impressive as it is, the Grand Canyon's not that complicated geologically; it's made of layers of sedimentary rock, most of them relatively undeformed, one on top of the other from the oldest at the bottom to the newest at the top.  A layer cake of billions of years of Earth history, and a wonderful example of the principle of superposition -- that strata form from the bottom up.

However, Powell also noted something rather peculiar.  It's called the Great Unconformity.  In geologic parlance, an unconformity is a break in the rock record, where the layer below is separated from the layer above by a gap in time when either no rocks were deposited (in that location, at least), or the rocks that were laid down were later removed by some natural process.  At that stage in the science, Powell didn't know when exactly the Great Unconformity occurred, but it was obvious that it was huge.  Something had taken away almost a billion years' worth of rocks -- and, it was later found out, that same chunk of rock was missing not only at the future site of the Grand Canyon, but across most of North America.

It was an open question as to why this happened, but one leading hypothesis was that it was massive glaciation.  Glaciers are extraordinarily good at breaking up rocks and moving them around, as I find out every time I dig in my garden and my shovel runs into the remnants of the late Pleistocene continental glaciation.  At that point, where my house is would have been under about thirty meters of ice; the southern extent is the Elmira moraine, a line of low hills thirty miles south of here, left behind when the glaciers, pushing piles of crushed rock and soil ahead of them like a backhoe, began to melt back and left all that debris for us gardeners to contend with ten thousand years later.

There was a time in which the Earth was -- as far as we can tell -- completely covered by ice.  The Cryogenian Period, during the late Precambrian, is sometimes nicknamed the "Snowball Earth" -- and the thawing might have been one contributing factor to the development of complex animal life, an event called the "Cambrian explosion," about which I've written before.

The problem was, the better the data got, the more implausible this sounded as the cause of the Great Unconformity.  The rocks missing in the Great Unconformity seem to have preceded the beginning of the Cryogenian Period by a good three hundred million years.  And while there were probably earlier periods of worldwide glaciation -- perhaps several of them -- the fact that the Cryogenian came and went and didn't leave a second unconformity above the first led scientists away from this as an explanation.

Now, a new paper in Proceedings of the National Academy of Sciences, written by a team led by Francis Macdonald of the University of Colorado - Boulder, has come up with evidence supporting a different explanation.  Using samples of rock from Pike's Peak in Colorado, Macdonald's team used a clever technique called thermochronology to estimate how much rock had been removed.  Thermochronology uses the fact that some radioactive elements release helium-4 as a breakdown product, and helium (being a gas) diffuses out of the rock -- and the warmer it is, the faster it leaves.  So the amount of helium retained in the rock gives you a good idea of the temperature it experienced -- and thus, how deeply buried it was, as the temperature goes up the deeper down you dig.

What this told Macdonald's team is that the Pike's Peak granite, from right below the Great Unconformity, had once been buried under several kilometers of rock that then had been eroded away.  And from the timing of the removal -- on the order of a billion years ago -- it seems like what was responsible wasn't glaciation, but the formation of a supercontinent.

But not Pangaea, which is what most people think of when they hear "supercontinent."  Pangaea formed much later, something like 330 million years ago, and is probably one of the factors that contributed to the massive Permian-Triassic extinction.  This was two supercontinents earlier, specifically one called Rodinia.  What Macdonald's team proposes is that when Rodinia formed from prior separate plates colliding, this caused a huge amount of uplift, not only of the rocks of the continental chunks, but of the seafloor between them.  A similar process is what formed the Himalayas, as the Indian Plate collided with the Eurasian Plate -- and is why you can find marine fossils at the top of Mount Everest.

[Image is in the Public Domain]

When uplift occurs, erosion increases, as water and wind take those uplifted bits, grind them down, and attempt to return them to sea level.  And massive scale uplift results in a lot of rock being eroded.

Thus the missing layers in the Great Unconformity.

"These rocks have been buried and eroded multiple times through their history," study lead author Macdonald said, in an interview with Science Daily.  "These unconformities are forming again and again through tectonic processes.  What's really new is we can now access this much older history...  The basic hypothesis is that this large-scale erosion was driven by the formation and separation of supercontinents.  There are differences, and now we have the ability to perhaps resolve those differences and pull that record out."

What I find most amazing about this is how the subtle chemistry of rock layers can give us a lens into the conditions on the Earth a billion years ago.  Our capacity for discovery has expanded our view of the universe in ways that would have been unimaginable only thirty years ago.

And now, we have a theory that accounts for one of the great geological mysteries -- what happened to kilometer-thick layers of rock missing from sedimentary strata all over North America.

John Wesley Powell, I think, would have been thrilled.

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This week's Skeptophilia book of the week is six years old, but more important today than it was when it was written; Richard Alley's The Two-Mile Time Machine: Ice Cores, Abrupt Climate Change, and Our Future.  Alley tackles the subject of proxy records -- indirect ways we can understand things we weren't around to see, such as the climate thousands of years ago.

The one he focuses on is the characteristics of glacial ice, deposited as snow one winter at a time, leaving behind layers much like the rings in tree trunks.  The chemistry of the ice gives us a clear picture of the global average temperature; the presence (or absence) of contaminants like pollen, windblown dust, volcanic ash, and so on tell us what else might have contributed to the climate at the time.  From that, we can develop a remarkably consistent picture of what the Earth was like, year by year, for the past ten thousand years.

What it tells us as well, though, is a little terrifying; that the climate is not immune to sudden changes.  In recent memory things have been relatively benevolent, at least on a planet-wide view, but that hasn't always been the case.  And the effect of our frantic burning of fossil fuels is leading us toward a climate precipice that there may be no way to turn back from.

The Two-Mile Time Machine should be mandatory reading for the people who are setting our climate policy -- but because that's probably a forlorn hope, it should be mandatory reading for voters.  Because the long-term habitability of the planet is what is at stake here, and we cannot afford to make a mistake.

As Richard Branson put it, "There is no Planet B."

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

Widening the Goldilocks Zone

The oft-quoted line from Jurassic Park, "Life finds a way," got interesting support from an (unrelated) pair of studies that came out this week, which show that life is a great deal more resilient than we realized.

The first, by a team led by Maxwell Lechte of McGill University, resulted in a paper that appeared in Proceedings of the National Academy of Sciences.  Entitled, "Subglacial Meltwater Supported Aerobic Marine Habitats During Snowball Earth," and looked at a curious (and to us, completely inhospitable) time in Earth's history.  Current models support the conclusion that for a significant chunk of time in the Precambrian Period, between 720 and 635 million years ago, the entire surface of the Earth was covered with ice.  Called the "Snowball Earth" period, it's long been a question in evolutionary biology how any living thing could survive this -- the entire land area of the Earth under a sheet of ice, and the ocean cut off from the atmosphere because its surface is frozen solid.

The authors think they've found the answer.  According to their models, subglacial meltwater streaming through stress cracks in the ice would have been sufficient to generate oxygen-rich "oases" in which life could have survive the deep freeze.  The authors write:

The Earth’s most severe ice ages interrupted a crucial interval in eukaryotic evolution with widespread ice coverage during the Cryogenian Period (720 to 635 Ma).  Aerobic eukaryotes must have survived the “Snowball Earth” glaciations, requiring the persistence of oxygenated marine habitats, yet evidence for these environments is lacking.  We examine iron formations within globally distributed Cryogenian glacial successions to reconstruct the redox state of the synglacial oceans. Iron isotope ratios and cerium anomalies from a range of glaciomarine environments reveal pervasive anoxia in the ice-covered oceans but increasing oxidation with proximity to the ice shelf grounding line.  We propose that the outwash of subglacial meltwater supplied oxygen to the synglacial oceans, creating glaciomarine oxygen oases.  The confluence of oxygen-rich meltwater and iron-rich seawater may have provided sufficient energy to sustain chemosynthetic communities.  These processes could have supplied the requisite oxygen and organic carbon source for the survival of early animals and other eukaryotic heterotrophs through these extreme glaciations.

"The evidence suggests that although much of the oceans during the deep freeze would have been uninhabitable due to a lack of oxygen, in areas where the grounded ice sheet begins to float there was a critical supply of oxygenated meltwater," said study lead author Maxwell Lechte in a press release.  "This trend can be explained by what we call a ‘glacial oxygen pump’; air bubbles trapped in the glacial ice are released into the water as it melts, enriching it with oxygen...  The fact that the global freeze occurred before the evolution of complex animals suggests a link between Snowball Earth and animal evolution.  These harsh conditions could have stimulated their diversification into more complex forms."

The second study is of a very peculiar species of bacteria, Metallosphaera sedula, which is from a curious group of microbes called chemolithotrophs -- they "eat rocks" as part of their required metabolism.  Some chemolithotrophs break down minerals like pyrite (iron sulfide), but Metallosphaera is even weirder than that.  It requires minerals -- more specifically, the elements in those minerals -- found in significant quantities only in meteorites.

Metallosphaera sedula  [Image by T. Milojevic et al.]

In "Exploring the Microbial Biotransformation of Extraterrestrial Material on Nanometer Scale," by a team led by Tetyana Milojevic of the University of Vienna, we find out that this bizarre bacteria thrives only with provided with minerals rich with nickel and copper, and in fact was discovered on a stony meteorite called Northwest Africa 1172.

"Meteorite-fitness seems to be more beneficial for this ancient microorganism than a diet on terrestrial mineral sources," said lead author Milojevic in a press release in Science Alert.  "Our investigations validate the ability of M. sedula to perform the biotransformation of meteorite minerals, unravel microbial fingerprints left on meteorite material, and provide the next step towards an understanding of meteorite biogeochemistry."

Besides that, it also brings up a couple of interesting questions -- first, it immediately made me wonder about the largely-ignored idea of panspermia -- that the earliest life on Earth came here from elsewhere in the universe.  The objection has always been that it'd have to be a pretty hardy life form to survive both both the vacuum of interstellar space and the fiery descent and collision of the meteorite with Earth's surface.  The Milojevic et al. study suggests that the first part might be entirely possible -- if the earliest life forms were chemolithotrophs, there's no reason they couldn't have been out there on a piece of space rock, nestled in a crack and chowing down on the minerals.

The other question, though, it the extent to which we're doing the reverse -- bringing terrestrial microbes out into space, contaminating every world we visit.  The conventional wisdom always was that the trip through space would effectively destroy any microorganisms riding on the outside of the spacecraft, but Metallosphaera sedula shows that might be more of an issue than we thought.

In any case, it does show that life is a great deal more resilient than we ever dreamed, further bolstering my contention that it's common out there in the universe.  The so-called "Goldilocks Zone," in which there are Earth-like conditions that foster the generation of life, might be a great deal larger than we ever dreamed.

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Long-time readers of Skeptophilia have probably read enough of my rants about creationism and the other flavors of evolution-denial that they're sick unto death of the subject, but if you're up for one more excursion into this, I have a book that is a must-read.

British evolutionary biologist Richard Dawkins has made a name for himself both as an outspoken atheist and as a champion for the evolutionary model, and it is in this latter capacity that he wrote the brilliant The Greatest Show on Earth.  Here, he presents the evidence for evolution in lucid prose easily accessible to the layperson, and one by one demolishes the "arguments" (if you can dignify them by that name) that you find in places like the infamous Answers in Genesis.

If you're someone who wants more ammunition for your own defense of the topic, or you want to find out why the scientists believe all that stuff about natural selection, or you're a creationist yourself and (to your credit) want to find out what the other side is saying, this book is about the best introduction to the logic of the evolutionary model I've ever read.  My focus in biology was evolution and population genetics, so you'd think all this stuff would be old hat to me, but I found something new to savor on virtually every page.  I cannot recommend this book highly enough!

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

Thawing the snowball

One of the frightening things about a system in equilibrium is what happens when you perturb it.

Within limits, most systems can recover from perturbation through some combination of negative feedbacks.  An example is your body temperature.  If something makes it goes up -- exercise, for example, or being outside on a hot, humid day -- you sweat, bringing your temperature back down.  If your body temperature goes down too much, you increase your rate of burning calories, and also have responses like shivering -- which brings it back up.  Those combine to keep your temperature in a narrow range (what the biologists call homeostasis).

Push it too much, though, and the whole thing falls apart.  If your temperature rises beyond about 105 F, you can experience seizures, convulsions, brain damage -- or death.  Your feedback mechanisms are simply not able to cope.

This, in a nutshell, is why climate scientists are so concerned about the effects of anthropogenic carbon dioxide.  Within limits -- as with your body temperature -- an increase in carbon dioxide results in an increase in processes that remove the carbon dioxide from the atmosphere, and the whole system stays in equilibrium.  There is a tipping point, however.

The problem is that no one knows where it is -- and whether we may have already passed it.

A new piece of research from the Virginia Polytechnic Institute has indicated that this flip from stability to instability may be fast and unpredictable.  A paper authored by a team led by paleobiologist Shuhai Xiao, that came out last month in Geology, looks at one of the main destabilization events that the Earth has ever experienced -- when the "Snowball Earth" thawed out in the late Precambrian Period,  635 million years ago.

Artist's conception of the Precambrian Snowball Earth [Image is in the Public Domain, courtesy of NASA/JPL]

Xiao and his team studied rocks from Yunnan and Guizhou, China, that are called cap carbonates.  They are made of limestone and dolomite and are deposited quickly in marine environments when the carbon dioxide content of the atmosphere spikes, leading to a dramatic temperature increase and a subsequent increase in absorption of carbonates into seawater (and ultimately deposition of those carbonates on the seafloor).  The cap carbonates Xiao et al. studied were dated to between 634.6 and 635.2 million years old, which means that the entire jump in both temperature and carbon dioxide content took less than 800,000 years.

So in less than a million years, the Earth went from being completely covered in ice to being subtropical.  The jump in global average temperature is estimated at 7 C -- conditions that then persisted for the next hundred million years.

Xiao et al. describe this as "the most severe paleoclimatic [event] in Earth history," and that the resulting deglaciations worldwide were "globally synchronous, rapid, and catastrophic."

Carol Dehler, a geologist at Utah State University, is unequivocal about the implications.  "I think one of the biggest messages that Snowball Earth can send humanity is that it shows the Earth’s capabilities to change in extreme ways on short and longer time scales."

What frustrates me most about today's climate change deniers is that they are entirely unwilling to admit that the changes we are seeing are happening at an unprecedented rate.  "It's all natural," they say.  "There have been climatic ups and downs throughout history."  Which is true -- as far as it goes.  But the speed with which the Earth is currently warming is faster than what the planet experienced when it flipped between an ice-covered frozen wasteland and a subtropical jungle.  It took 800,000 years to see an increase of the Earth's average temperature by 7 degrees C.

The best climate models predict that's what we'll see in two hundred years.

And that is why we're alarmed.

It's unknown what kind of effect that climate change in the Precambrian had on the existing life forms.  The fossil record just isn't that complete.  But whatever effect it had, the living creatures that were around when it happened had 800,000 years to adapt to the changing conditions.  What's certain is that an equivalent change in two centuries will cause massive extinctions.  Evolution simply doesn't happen that quickly.  Organisms that can't tolerate the temperature fluctuation will die.

We can only speculate on the effects this would have on humanity.

This is clearly the biggest threat we face, and yet the politicians still sit on their hands, claim it's not happening, that remediation would be too costly, that we can't prevent it, that short-term profits are more important than the long-term habitability of the Earth.  Our descendants five hundred years from now will look upon the leaders from this century as having completely abdicated their responsibility of care for the people they represent.

Presuming we still have descendants at that point.

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This week's Skeptophilia book recommendation combines science with biography and high drama.  It's the story of the discovery of oxygen, through the work of the sometimes friends, sometimes bitter rivals Joseph Priestley and Antoine Lavoisier.   A World on Fire: A Heretic, an Aristocrat, and the Race to Discover Oxygen is a fascinating read, both for the science and for the very different personalities of the two men involved.  Priestley was determined, serious, and a bit of a recluse; Lavoisier a pampered nobleman who was as often making the rounds of the social upper-crust in 18th century Paris as he was in his laboratory.  But despite their differences, their contributions were both essential -- and each of them ended up running afoul of the conventional powers-that-be, with tragic results.

The story of how their combined efforts led to a complete overturning of our understanding of that most ubiquitous of substances -- air -- will keep you engaged until the very last page.

[Note:  If you purchase this book by clicking on the image/link below, part of the proceeds will go to support Skeptophilia!]