Anoxic Conditions From Everest to Europa: Swamps, Fossils, Naked Mole Rats, and the Hunt for Extraterrestrial Life

Above elevations of 6500 meters (21,300 feet), most climbers tend to start using supplemental oxygen.  At altitudes higher than this, oxygen is spread so thin that humans can have a very tough time breathing.  Even people who come from sea level to my hometown of Boulder, Colorado at an elevation of 1,655 meters (5,430 feet) often get altitude sickness, and there's still a whole lot of altitude to go before you even get to Everest Base Camp.  Most birds don't fly as high as the summit of Mt. Everest, because most birds have no reason to fly that high.  However, for the bar-headed goose, the Himalayas form an unfortunate, but not impassable, barrier between their winter feeding grounds in India and their Tibetan nesting grounds.  These geese have been reported flying over some of the highest Himalayan peaks, and they're not the only ones that fly this high.  On November 29th, 1973, a Rüppell's griffon, a type of Old World vulture, collided with an airplane at an altitude of 11280 meters (37,000 feet).  By comparison, oxygen cylinders are recommended for sailplane pilots flying over 3660 meters (12,000 feet)!

Here we have a beautiful (and extraordinarily neat) size comparison and altitude chart of a number of things covered in the post, including the altitude of Denver, the summit of Mt. Everest, the upper extent of the range of the snow leopard, and the height at which the Rüppells griffon got sucked into the jet engine.  I've also thrown in some other helpful and fun things for comparison as well.

Part of what helps birds survive at altitudes that could kill a human is a series of air sacs that allow air to flow in one direction through the body of the bird.  In humans, the air we breath in and out travels back and forth along the same tubes.  In birds, as well as some of their close dinosaurian cousins, these air sacs would have have allowed the air to flow more efficiently through their bodies.  While this is simply one of many adaptations that can help birds fly at incredibly high altitudes, other animals have evolved other adaptations to assist in high altitude living.  Scientists have determined that changes in the genes EGLN1 and EPAS1 are linked with animals living in oxygen impoverished environments, such as the snow leopard, humans native to Tibet, and naked mole rats.  Naked mole rats live in underground colonies of 20-300 individuals, and are one of two species of mammal that can be classified as "eusocial," meaning that their colonies display a caste system (similar to the social structure seen in ant and termite colonies).  These underground colonies are poorly ventilated, which means that as the mole rats inhale oxygen and exhale carbon dioxide, CO2 concentrations can increase to levels that would be unsafe for humans.  Fortunately, naked mole rats are well adapted to breathing very little oxygen, and their brains seem incapable of registering pain upon contact with acids, which is thought to help them in these CO2 rich confines.  They also demonstrate similar changes in the aforementioned genes as snow leopards and the Tibetan people, indicating another adaptation to these low oxygen (or hypoxic) conditions.

A group of naked mole rats all huddled together at the Cheyenne Mountain Zoo in Colorado Springs, Colorado.  Look at all of that eusociality!

Although hypoxic conditions can bode ill for human climbers and gregarious colonial rodents, low oxygen conditions can be great for paleontologists.  When oxygen levels drop to nearly zero, anoxic conditions prevail, and bacterial decomposition of organic material is greatly reduced.  This can be a major factor when it comes to soft-tissue preservation, such as feathers and skin.  A FEW WEEKS AGO, we talked about several famous fossil sites called Lagerstätten (a German term meaning "mother lode"), that are set apart from other fossil deposits due to the quality and/or quantity of the fossils discovered there.  One of the most famous examples is the Cambrian-aged Burgess Shale in British Columbia, Canada.  Abrupt burial of the 500 million year old organisms, coupled with the anoxic conditions that prevailed at the bottom of this body of water, ensured that these soft-bodied organisms would be preserved in exquisite detail.

A drawing of Opabinia, one of the many creatures that inhabited the Cambrian aged Burgess Shale in British Columbia, Canada.  Photo Credit: Sam Lippincott

Why do swamps often have that rotten egg smell?  Believe it or not, the answer is closely related to what we've already been talking about!  Under hypoxic or anoxic conditions, bacteria that use oxygen (O2) sometimes have to make do with sulfur (S).  If you look at a periodic table, you can see that sulfur (element #16) is directly below oxygen (element #8).  In the periodic table, each group (or column) of elements has very similar chemical properties, which means each element will react in a similar fashion.*  For the bacteria that can't get enough oxygen, they will sometimes turn to its close cousin sulfur instead.  Below is the chemical formula for cellular respiration, which is what these bacteria do, as well as some of the cells in humans.  On the left, we have the inputs: glucose (C6H12O6), and oxygen (O2).  When we breath in air, we are bringing oxygen into our lungs, and we can get glucose from the foods we eat.  On the right of the arrow, we have the outputs: water (H20), carbon dioxide (CO2), and energy.  Remember how we talked about the CO2 concentrations in naked mole rat burrows?  CO2 is one of the products of respiration, and one that can be harmful in large doses.  Energy is another product of respiration, which is the fuel that cells need to do their job.  In places where there is less oxygen input (such as at the top of Mt. Everest or in a naked mole rat burrow), the cells don't get as much energy output, and they can't do their job as well.

Now, instead of having oxygen as one of the inputs of cellular respiration, let's try sticking oxygen's close cousin, sulfur, into the equation to see what will happen.  As you can see below, the glucose on the left of the equation remains unaffected, as does the carbon dioxide output on the right of the equation.  But instead of having water (H2O) as another one of the outputs, we now see a molecule with the formula H2S.  Instead of forming water (hydrogen oxide), we have now formed a closely related molecule, hydrogen sulfide.  In swamps, large amounts of organic material leads to lots of bacteria and bacterial decomposition, which in turn can lead to lots of the oxygen being used up in the water.  That's when these bacteria start using sulfur to make their energy, producing hydrogen sulfide, with that characteristic rotten egg smell.  Even with this sulfur replacement, sometimes the bacteria just can't keep up with the amount of vegetation that is deposited in the swamp, and the organic material builds up.  If the rate at which the vegetation accumulates exceeds the rate which the bacteria can decompose the vegetation, then you have coal formation potential sometime in the future.

Let's take this one step further.  In normal respiration, where oxygen is one of the inputs and water (H2O) is one of the outputs, carbon dioxide (CO2) is another one of the outputs.  If animals and bacteria keep using up oxygen and turning it into carbon dioxide, why haven't we run out of oxygen?  Will we run out one day?  Fortunately, for the time being, plants have got our back, by undergoing a process called photosynthesis.  Photosynthesis is almost the exact opposite of respiration: carbon dioxide and water are the inputs, and glucose and oxygen are the outputs.  However, unlike respiration, light is one of the inputs of photosynthesis.  In the 1700s, a man named Joseph Priestly did experiments in which he sealed a mouse in a jar, and waited to see what happened.  The mouse, as you could probably predict, suffocated and died.  It used up its oxygen to create energy (as well as carbon dioxide), and eventually ran out of oxygen.  (This is why it's important not to put animals into completely sealed jars with no airflow, as they will suffocate.)  However, if he put a plant into the same jar as the mouse, the mouse didn't suffocate.  We now know that is because, as the mouse used up the oxygen, creating carbon dioxide, the plant would use the carbon dioxide, ultimately creating more oxygen.

As you probably know, plants need light to survive, and as we mentioned before, that's because light is one of the inputs of photosynthesis.  No light, no photosynthesis.  No photosynthesis, your plant dies.  For many years, scientists assumed that all life on Earth was directly dependent on the Sun for its energy.  That is, until 1977, when scientists discovered entire communities of biological organisms living thousands of meters beneath the surface of the ocean, too far from any sunlight to undergo photosynthesis.  So what was going on?  How were these communities able to survive without access to the sunlight?

Hydrothermal vents are essentially underwater hot springs that form along tectonic boundaries thousands of meters beneath the surface of the ocean.  These underwater vents spew different compounds containing sulfur into the surrounding water, just like aboveground geysers do, too.  (If you have ever been to Yellowstone National Park, then you might even remember the rotten egg smell.)  Some bacteria that surround these vents are actually able to use these sulfur-containing compounds to create the energy needed to undergo a process similar to photosynthesis, called chemosynthesis (consult the equation below).  Chemosynthesis is very similar to photosynthesis, with a few key differences, the biggest difference being the sulfur reactions vs. sunlight as one of the inputs.  You can also see that, instead of having water (H2O) as an input like in photosynthesis, chemosynthesis instead uses hydrogen sulfide (H2S) as an input.  Then, instead of producing oxygen, the chemosynthetic organisms produce water and sulfur.  You can compare it to the oxygen-poor respiration equation that we talked about with the swamps, and see that it is similar to that equation as well, simply flipped around.

But that's not all.  Scientists have taken this idea a step (or rather, one giant leap) further.  The search for life on other planets thus far has yielded nothing, but that doesn't mean it's not there.  It is now realized that some of the factors that were once thought to limit the development of life, such as sunlight, might not be as crucial as we once thought, and the hydrothermal vent communities have been crucial in the maturation of these ideas.  Some scientists suspect that life could exist on Mars by using chemosynthesis, but a new candidate has been receiving an increasing amount of attention: one of Jupiter's moons, Europa.  Icier than the planet Hoth, Europa is now thought to have an ocean of liquid water up to 160 km (100 miles) deep surrounding the solid, rocky mantle, following the discovery of a magnetic field surrounding the moon, similar to the magnetic field that surrounds the Earth.

What keeps the liquid ocean of Europa from freezing solid?  Jupiter is pretty far from the Sun, and even Mars, which is much closer to both the Sun and the Earth than Jupiter is, has had its water frozen for millennia.  It's thought that the gravity exerted by the enormous mass of Jupiter continually pushes and pulls, or tidal stresses, on its moons, which keep the planets from becoming tectonically inactive, like Mars.  Io, another of Jupiter's moons slightly larger than our Moon, is the most geologically active body in our Solar System.  The tidal stresses from Jupiter exerted on Io apparently make Io's ground itself buckle up and down, similar to the tides we experience here on Earth, except that instead of water moving up and down 18 meters (60 feet), its solid ground moving up and down up to 100 meters (330 feet!)  It's these same tidal stresses that make Io so geologically and volcanically active that help keep Europa from freezing solid.  It has been hypothesized that the tidal flexing might also create hydrothermal vents on the bottom of Europa's oceans, and it shouldn't take too much thinking to realize what that might mean: the potential for extraterrestrial life!

*For example, we humans, as well as all known lifeforms, are carbon-based.  In science fiction, such as Star Trek and Transformers, you will often hear about "silicon-based lifeforms."  Why silicon, as opposed to any other element?  If you look at the periodic table, silicon is in the same group as carbon, and situated right beneath it, and therefore has very similar chemical properties as carbon.



Works Cited:

Grès à Voltzia: Mid-Triassic French Lagerstätten

In our last post*, we got our first glimpse of some of the flora and fauna that inhabited the earth 240 MYA, in the Mid Triassic Period.  In that post, we mostly looked at the aquatic environments, fossils found at a fascinating place in Italy called Monte san Giorgio.  In good time, we will learn more about the terrestrial ecosystems and what lived on land.  But first, let us look between the aquatic and the terrestrial.  Let's look at the seashores of this ancient Earth.

To gain a better understanding of what lived on the margins of the oceans, we can look at Grès à Voltzia in France.  The importance of this site lies not just in the preservation of a large number of different organisms, but in the exceptional quality of said preservation.  Grès à Voltzia is considered a Lagerstätte, a German word referring to fossil sites that feature remarkable detail in the preservation of fossils, with famous examples including the Solnhofen Limestone in Germany and the Green River Formation in Wyoming.  The depositional environment that would one day become Grès à Voltzia featured deltas very close to the shore, and were home to many animals.  This prime habitat resulted in the burial of both terrestrial and marine animals, painting an even more complete picture of this ecosystem.

Here we have a picture lifted from my Instagram that shows three very different animals from the aforementioned Lagerstätten. What ties these three animals is their common ability to fly.  On the right, we have pictures of two fossil casts from the Solnhofen Limestone in Germany, deposited about 150 MYA.  Archaeopteryx, the primitive bird/dinosaur link, is on top, and Pterodactylus, a type of pterosaur, is on the bottom.  The picture on the right is of a bat from the Eocene of Wyoming, found in the Green River Formation, deposited approximately 50 MYA.  Despite its age, Icaronycteris was fairly similar to modern bats.  All three of these animals convergently evolved flight, and were not derived from a common ancestor.

Along the shores of these 240 MY old rivers, horsetails and and ferns grew in abundance, as well as several different types of gymnosperms.  Large amphibians such as Eocyclotosaurus made their home in these waterways, as they were tied to moist environments just like modern amphibians are today.

Horseshoe crabs like Limulitella, very similar to modern horseshoe crabs, are commonly found, as are many types of crustaceans, such as Antrimpos, a type of shrimp.

Insect larvae includes dipteran (true flies), odonatopteran (dragonflies and damselflies) and ephemeropteran (mayflies).  Annelids (segmented worms like the modern earthworm) have also been discovered here, as well as fish and a jellyfish.

The horsetails, such as Equisetites, grew along the edges of the water, while the gymnosperms grew further inland, probably reaching at least several meters in height.

A large number of insects, including the dipterans and ephemeropterans that we already mentioned, lived here.  Proto-cockroaches (blattopterans), beetles (coleopterans), and hemipteroids were all present, as well as myriapods (centipedes and millipedes), and spiders.  A strange mixture of modern and exotic looking animals to be certain!

Next time, we will be continuing our investigation regarding the flora and fauna of the Mid Triassic by learning about two North American geologic formations that might reveal a bit more about the terrestrial ecosystems.  Join us!

*As those of you who are familiar with myself and this blog, you are likely familiar with the fact that once I start talking, it takes a good deal to make me shut up.  The same is true for writing this blog.  When I originally came up with the idea to do a post about the flora and fauna that inhabited the Earth 240 MYA, flora and fauna that many people, myself included, are relatively unfamiliar with, it was supposed to be a relatively short post, maybe four or five paragraphs in length.  Instead, I ended up just writing and writing and writing.  I realized, as I often do, that A) so few people would be reading these posts to begin with, and B) those people who do wind up reading these posts would likely not have stuck around for an immense post that talks about everything from the ichthyosaurs of Italy, the stromatolites of Colorado, the insects of France, the communal latrines of Tasmanian devils, the lack of communal latrines of Maiasaura, the communal latrines of dicynodonts (yes, poop is cool), the heterodont condition of primitive whales, and everything in between, that it made more sense to split the post up.  This is the second installment of five (so far, at least) regarding the flora and fauna of the Mid Triassic Period, approximately 240 MYA.  It now occurs to me that I probably lost most of you in this long-winded exposition.  I don't want to just delete all this though, as future generations will find this fascinating glimpse into my thought processes an untapped reservoir of knowledge that is absolutely vital to an understanding of the ultimate being I shall become.  I think I will just make this whole thing an endnote.

Works Cited: