Off the keyboard of Dead Rat Reporter
Follow us on Twitter @doomstead666
Friend us on Facebook
Published on The Doomstead Diner on December 3, 2016
Discuss this article at the Environment Table inside the Diner
Peter D. Ward is a paleontologist who has authored a number of books for the general reader, often on the subject of mass extinction. His most successful book was Rare Earth: Why Complex Life is Uncommon in the Universe (with Donald Brownlee, 2001). His latest is, A New History of Life: The Radical New Discoveries about the Origins and Evolution of Life on Earth (2016). For this book, Ward’s co-author is Joe Kirschvink, a prominent geobiologist. Through three hundred and fifty-six pages, they survey the three and a half billion years of Evolution, drawing largely from recent scientific papers. Rare Earth and A New History of Life serve as bookends to a very pessimistic conclusion: Fermi’s Question (aka his Paradox) is not paradoxical at all. That our species even exists is the non-supernatural definition of a miracle.
The ‘radical thesis’ of A New History of Life consists of three interconnected themes:
-Planetary catastrophe has been the principal driver of Evolution.
-Radical changes in the concentrations of three simple gases, oxygen, carbon dioxide and hydrogen sulfide in the atmosphere or the oceans, dictate the fate of Life.
-Ecosystems perish and novel ones emerge because of these events.
Now to our story, thus far:
4.567 billion years ago (now that is a neat mnemonic!), two rocky planets in nascent orbits around our Sun crossed paths into collision. Their dense cores of iron and nickel melded together within what became our Earth, while a halo of vaporized rock condensed into our companion Moon. Rare Earth contains a list of vital consequences that result from this single astronomical accident. Some that I recall from it:
-The Earth received a disproportionately large metallic core, one that provides a very strong magnetic field that shields us from cosmic radiation and breaks the solar wind.
-With that core the Earth acquired an extra dose of uranium and thorium, and the internal heat from that boosted radioactivity has intensified and prolonged its geological transformations. In contrast, the Moon received very little of this fissionable material and has long been geologically dead. Moreover, the mass of the Moon formed largely from ejected silicate rock, and the loss of this lighter material from Earth has made its crust relatively thin, which permits plate tectonics and continuous volcanic emissions.
-The collision knocked Earth onto a tilted axis, which creates the seasons of each year and influences longer cycles of climate.
-Planets can wobble, and the relative large size of the Moon stabilizes Earth’s orbital axis.
http://www.space.com/12464-earth-moon-unique-solar-system-universe.html
-The Moon has progressively slowed Earth’s rotation to lengthen its day. It stirs the ocean’s tides, and gives illumination to the night.
In the absence of these phenomena, Life on Earth would be very different.
A recent paper offers another significant hypothesis
Earth's carbon points to planetary smashup
"Research by Rice University Earth scientists suggests that virtually all of Earth's life-giving carbon could have come from a collision about 4.4 billion years ago between Earth and an embryonic planet similar to Mercury."
"… a new answer to a long-debated geological question: How did carbon-based life develop on Earth, given that most of the planet's carbon should have either boiled away in the planet's earliest days or become locked in Earth's core?"
http://phys.org/news/2016-09-earth-carbon-planetary-smashup.html#jCp
In the beginning, The Big Bang created the Heavens. Eight billion or so years later, a colossal accident created the Earth, and it was good. Catastrophe appears to be the Mother of Us All.
From astro- and geophysics, we move to biophysics, and the actual Creation of Life. This pathway of biochemical synthesis may always remain unresolved, but in A New History of Life Ward and Kirschvink find favor with Life’s possible origin on the planet Mars. In this scenario, ancient Mars provided the right environmental conditions to jumpstart primitive cells, which then traveled to sister Earth as ejecta from asteroid collisions. If true, this would be another addition to the Rare Earth hypothesis – the fortuitous proximity of a seedbed planet.
Whatever Life’s origins, it found an Earth little like ours. The most critical difference was the atmosphere. Currently, it is primarily nitrogen and oxygen, with ‘trace amounts’ of water vapor, carbon dioxide and argon. The primordial atmosphere was nitrogen, methane, sulfur dioxide, carbon monoxide, carbon dioxide and water vapor, with near total absence of oxygen. It is important to note that the intense greenhouse effect of this ancient atmosphere existed with a much fainter solar output. As the Sun ages, its output of energy grows, and will eventually boil Life on Earth away.
In the absence of free, molecular oxygen, the metabolism of the original life forms used sulfur. There is speculation that the first microbes were chemoautotrophs that consumed the hydrogen sulfide and carbon monoxide that spewed from thermal vents in the ocean floor, with the clear irony being that those gases are extremely toxic for much of present Life. Hydrogen sulfide (H2S) is a gas released by volcanic activity, and the original photosynthetic pathway used it instead of water (H2O) as the requisite donor of electrons. Photosynthetic sulfur bacteria still exist and they remain very consequential.
A billion years might have elapsed before an alternative a photosynthetic pathway evolved, one that substituted water for hydrogen sulfide. These emergent cyanobacteria then had a twin advantage for evolutionary success. First, while hydrogen sulfide is relatively scarce, there were vast oceans of water, the feedstock of their oxygen-based metabolism. Second, the free oxygen that their new model of photosynthesis produced as its by-product would directly kill their sulfur-using, anaerobic competition. That free oxygen is highly toxic to hydrogen sulfide using organisms, and vice versa, is a key part of the second major theme of Ward and Kirschvink.
With the appearance of oxygenated photosynthesis came the first, and perhaps greatest, of Earth’s Mass Extinction Events — the Great Oxygen Event, or Catastrophe. Not only did the oxygen makers drive the original, sulfur-using microbial ecosystem to near extinction, their exuberant growth drew down (in as little as a million years) the high carbon dioxide content of the Earth’s atmosphere, converting it to a layer of organic detritus on the ocean floor. The free oxygen also reacted with methane, scrubbing this more potent greenhouse gas from the atmosphere as well. In those times of a cooler Sun, the greatly diminished greenhouse effect allowed the oceans to freeze, almost completely solid. Co-author Kirschvink was the first to formulate and name this second phase of mass extinction. He called it Snowball Earth.
There followed a pulse of such Cryogenic Extinctions. Each time the planet froze up, so did the cyanobacteria, which permitted the carbon dioxide from volcanoes to accumulate and increase the greenhouse effect. But with each thaw, the cyanobacteria bloomed again, plunging the planet back to Snowball. The authors think it took 200 million years to establish a more stable carbon cycle, where microbial scavengers metabolized the dead material from the ocean bottoms and respired it as carbon dioxide to sustain a warmer planet.
However, in that shallow, warming ocean, the usurped sulfur-based organisms then resurged and retook Earth from their oxygenated rivals, by turning the oceans and atmosphere toxic with rising concentrations of hydrogen sulfide [search Canfield Oceans]. For a period stretching from two to one billion years ago, oxygenated life remained suppressed. Green and purple sulfur bacteria dominated the warm oceans; their hydrogen sulfide wafted high into the atmosphere and reacted with the ozone layer; high levels of ultraviolet radiation beamed through and sterilized the Earth’s surface. Throughout this time, the level of atmospheric oxygen was below ten percent, a threshold necessary for animal life. After searching its strata in vain for complex life, paleontologists dubbed this period as ‘The Boring Billion’. More pointedly, Ward and Kirschvink describe this long reign of the sulfur bacteria as the ‘Evil Empire’.
What brought the ended the Boring Billion? Perhaps it was the rise of the continents. Iron eroding from them and reacting with H2S in the oceans, precipitated out the sulfur as iron pyrite. Starved of their feedstock, the sulfur bacteria declined and the oxygen-lovers bloomed again. Two more Snowball episodes followed, but as a more stable carbon cycle became established, the level of atmospheric oxygen continued to rise, and the sulfur bacteria retreated into marginal niches, such as the bottom of the current Black Sea, where they remain today.
However, fabled Planet Gaia still failed to emerge.
The evolution of Life on Earth would continue from careen from one Mass Extinction Event to another. 635 billion years ago, the oxygen level rose high enough for multicellular animals to make their belated appearance. And it appears that these motile and hungry organisms caused the late Vendian-Endiacaran Extinction, by grazing away the former placid ecosystem.
New fossil evidence supports theory that first mass extinction engineered by early animals
https://www.eurekalert.org/pub_releases/2016-07/vu-nfe072916.php
The late Cambrian Extinction followed next, where most species of trilobites and many unique animal body plans were lost forever. An anomalous shifting of the Earth’s crust and mantle around its core and spin axis may have brought about this one, a theory called True Polar Wander.
Planet Earth may have 'tilted' to keep its balance, say scientists
http://www.princeton.edu/main/news/archive/S15/64/72A37/index.xml?section=newsreleases
Next came the Ordovician Mass Extinction, the first of the so-called ‘Big Five’ events. Mainly, this wiped out tropical species, by a combination of planetary cooling and great changes of sea level. The cause might have again been geological, another episode of True Polar Wander, but recently has come an alternative explanation: Complex plants were moving onto dry land.
Weathering of rocks by mosses may explain climate effects during the Late Ordovician
"During the Ordovician period, the concentration of CO2 in the earth's atmosphere was about eight times higher than today. It has been hard to explain why the climate cooled and why the Ordovician glaciations took place. A new study, published in Nature Communications, shows that the weathering of rock caused by early non-vascular plants had the potential to cause such a global cooling effect.
"Although they do not have real roots, they affect the surfaces on which they grow: the release of various organic acids dissolves underlying rock minerals. This process of dissolution and chemical transformation of rock minerals is called chemical weathering. Non-vascular plants and lichens may considerably increase weathering rates of the rock surfaces on which they grow. This has important implications for the climate system, since chemical weathering of silicate rocks such as granite results in a drawdown of atmospheric CO2 and may therefore lead to global cooling."
https://www.eurekalert.org/pub_releases/2016-07/su-wor070716.php
According to Ward and Kirschvink, a more general mechanism for mass extinction now emerges.
"They [green and purple sulfur bacteria] can be thought of as the evil empire. And in the Devonian, Permian, Triassic, Jurassic and Middle Cretaceous, this empire stuck back…"
The Devonian Mass Extinction took three quarters of Earth’s species, in particular the marine animals. The authors speculate this is the first of what Ward has termed Greenhouse Mass Extinctions. The killing mechanism: increased volcanic activity strengthens the greenhouse effect, bringing planetary warming. As the difference in temperature between the poles and tropics diminishes, the prevailing winds and ocean currents stall. Unstirred, the oceans stratify, and at their bottoms, oxygen declines. There, the absence of free oxygen permits the sulfur bacteria to bloom, and the Evil Empire makes its toxic return.
The Permian Mass Extinction shows clear evidence of this scenario. This is the worst of the extinction events, with maybe 96% of species perishing – paleontologists refer to it as ‘the Great Dying’. Beneath a greenhouse atmosphere, ocean temperatures spiked to 40C (104F) and on land, reached 60C (140F). As the oceans turned purple with sulfur bacteria, the hydrogen sulfide erased the ozone layer and tinted the sky to a toxic shade of green. In both air and water, the hydrogen sulfide reached levels that were lethal to most animal life. In addition, oxygen levels plummeted to between ten and fifteen percent and stayed there for five million years. At sea level, that oxygen content was the equivalent to what we find on high mountain peaks, so that most land elevations above a thousand meters would not support complex organisms at all. The ‘Great Dying’ might have occurred over a mere fifty thousand years but it took ten to twenty million years for biodiversity to recover.
The next Greenhouse Mass Extinction was protracted, with two or three phases of killing spread over millions of years. This one ended the Triassic and extended into the Jurassic. The authors propose (as does a stubborn clique of paleontologists) that the dinosaurs were already dying out from this Greenhouse mechanism, when the Chicxulub asteroid struck its coup de grace and ended the Cretaceous.
In all, Ward and Kirschvink offer a list of Ten Major Extinction Events. We currently experiencing Number Ten, titled as the Late Pleistocene-Holocene Mass Extinction. They cite its duration and cause:
"From 2.5 million years ago to today – climate change and human activities."
Ten major extinctions and the inadvertent, destructive properties of Life itself appear as the principal cause of seven or eight of them. To James Lovelock’s Gaia Hypothesis of a self-regulating Biosphere that maintains an Earth fit for life, Ward counters with his ‘Medea Hypothesis’:
"…multicellular life, understood as a superorganism, is suicidal; in this view, microbial-triggered mass extinctions are attempts to return the Earth to the microbial-dominated state it has been for most of its history. It is named after the mythological Medea, who killed her own children."
https://en.wikipedia.org/wiki/Medea_hypothesis
To characterize Life on Earth as a ‘super-organism’ with intentions is a stretch, but what is evident is that the Earth System is chaotic over long periods and its Biosphere frequently crashes, via the Greenhouse mechanism, to a more microbial ground state. In the fossil record, Ward and Kirschvink find evidence for more than ten such extinction events, of varying intensity. The last one came with the Paleo-Eocene Thermal Maximum (PETM) of 50 to 55 million years ago. They surmise the causative mechanism was a ‘new assassin’—the catastrophic release of methane clathrates – which accumulate from the activity of methanogenic bacteria. Their colleague Francesca McInerney helped them to provide a description:
"…this event is highly relevant to us humans, as the amount of carbon released into the atmosphere, about 12,000 to 15,000 gigatons, is roughly equivalent to what we humans are releasing over time by our industries and energy use. The temperature change caused [by] elevated greenhouse during the PETM made the world 5 to 9 centigrade warmer than it is now. The actual event lasted on order of 10,000 years. The plants that were present in her field area [now western North America]… were mainly plants that until the PETM lived in lower latitudes and thus at higher temperatures. After the event the old plants came back, as did the insects that were present prior to 10,000 years of literal hell on Earth. But not so the mammals. This event caused a wholesale change in the North American mammalian fauna."
If our Civilization proceeds on its current path, then several millennia in Hell may be the minimum we can expect. By the way, I myself am a North American mammal, as are most of the beings that I most cherish.
As much as the first animals, we know not what we do with our newfound powers:
"Although Darroch is studying events that took place 540 million years ago, he believes there is a message relevant for today. "There is a powerful analogy between the Earth's first mass extinction and what is happening today," he said. "The end-Ediacaran extinction shows that the evolution of new behaviors can fundamentally change the entire planet, and today we humans are the most powerful 'ecosystems engineers' ever known." [From ‘First Mass Extinction Engineered by Animals”]
That brings us to the third theme of A New History of Life: Ecosystems perish wholesale and different ones arise in their place. The mammal-like reptiles predominated before the Permian Mass Extinction Event. Afterward, Dinosaurs ruled the Earth, and the book details how they were better adapted than mammals to that hot world with lower levels of oxygen. In very ancient times, species of clams were the builders of the great marine reefs; long after these mollusks went extinct in hot, toxic seas, corals filled their empty niche. What is to build the next Great Barrier Reef? What is to replace us? The final chapter, under the sub-heading ‘The End of History’ contains a hint:
"A final prediction of Ward’s Medea hypothesis is that it should pertain to every planet with life, and that there is only one way out of this suicidal box that life creates simply through existing: intelligence. The intelligence to see the future. One such future is that our species expands its habitat first to Mars, then to the asteroid belts, and finally to other stars. Another future is that the carbon dioxide we are pumping into the atmosphere causes all the ice on Earth to melt, raising sea levels, slowing the thermohaline circulation patterns, bringing stagnation followed by anoxia to the ocean bottoms, and then into ever-shallower waters, at the same time liberating toxic levels of hydrogen sulfide to percolate out of every single ocean. In that future, only animals with very good gas masks will survive.
"History is an early warning system."
It is my opinion that humans are much too fragile, dull-witted and uncooperative to ever journey to other stars or even to settle Mars. I suppose the only intelligence that can replace us will be that of our machines – aluminum and titanium resist hydrogen sulfide better than flesh, electric motors run without oxygen, and silicon bonds are stable at much higher temperatures than those of carbon. Deus ex Machina, indeed.
To all of which, you may retort to me, as have others, “So what? That’s life. The dinosaurs were not missed, and neither will we be.”
The difference is that no other being has entered extinction fully aware of that finality; nor did it suffer the guilt of being complacent and complicit in the tragedy, no, in the crime and the sin of it all. So fuck all of you ‘minimizers’ and your shallow nihilism. Kurt Vonnegut Jr. once gave such an attitude to one of his most cynical characters:
"I realized," said Trout, "that God wasn't any conservationist, so for anybody else to be one was sacrilegious and a waste of time. You ever see one of His volcanoes or tornadoes or tidal waves? Anybody ever tell you about the lce Ages he arranges for every half-million years? How about Dutch Elm disease? There's a nice conservation measure for you. That's God, not man. Just about the time we got our rivers cleaned up, he'd probably have the whole galaxy go up like a celluloid collar. That's what the Star of Bethlehem was, you know.”
"What was the Star of Bethlehem?" said the driver.
"A whole galaxy going up like a celluloid collar," said Trout.
Breakfast of Champions, pg73
This essay began with the proposition that our existence is so improbable as to meet the definition of a miracle. Humans have fought and continue to fight bloody crusades over worthless holy places. What are we willing to do to preserve this Rare Earth and the miracle of our existence? If you think it is already too late, I must confess that you may be right. My hopes now depend on whether this Civilization, this Evil Empire, will quickly meet with Collapse and that will open a narrow space, a pathway to survival. The theme of A New History of Life, taken up by this pretentious essay, is that we are the very children of Catastrophe. So here is my prayer:
O Mother Catastrophe, please hear us now, and grant your children a merciful intervention.