Dinosaurs, Death, and the Long View
Warning: global chemistry may be hazardous to your health
Dinosaurs are always the belles of the ball. And maybe for good reason. There is a certain charisma that comes with otherworldly size. It’s hard to argue, figuratively or literally, with a 152,000 pound, 121-foot-long creature such as Patagotitan mayorum. But what may be even more compelling than their size is their staying power. Dinosaurs ruled the world for 200 million years.
That kind of time scale is hard to fathom intellectually, let alone viscerally. To wit, consider a comparison of the reptilian rule of the world to that of us lowly mammals, which, in effect, began with the advent of “civilization.”
Admittedly, defining civilization can be tricky. That notwithstanding, there are some basic hallmarks of civilized life: complex societies comprising systems of government and legal structures, written language or other modes of communication for transferring knowledge, concentrations of population, and division of labor. And by this simple measure, civilization dates to the Sumerians living between the Tigris and Euphrates rivers (southern Iraq), roughly 7,000 years ago. Seven thousand years.
So, to put the reign of our Brobdingnagian forebears in perspective, consider that the major developments of our entire civilization to date—the Mesopotamian, Egyptian, Asian, and Mayan Dynasties; the rise of religions; the Greek and Roman Empires; the Medieval Era; The Renaissance; The Enlightenment; the exploration of the globe; the First Industrial Revolution (steam engine); the Second Industrial Revolution (railroads, electricity, cars, and telephones); the World Wars; the Third Industrial Revolution (information and computing); and now the Fourth (AI and biotechnology)— could come and go, come and go, come and go, more than 28,000 times during the span of time the dinosaurs ruled the world.
Perhaps yet another reason the dinosaurs have captured our imaginations resides in the way they went out, which was, to say the least, dramatic.
Sixty-six million years ago, the Chicxulub Asteroid—6 miles in diameter—hit the Earth in the Yucatan Peninsula at approximately 45,000 miles per hour. It punched a hole 20 miles deep and 60 miles wide. The impact itself released so much energy—10 billion times that of the Hiroshima atomic bomb—that the earth instantly excavated from the crater showered the globe with molten rock, creating worldwide wildfires and an atmosphere that instantly broiled land-based animals. Then there were the seismic shaking and tsunamis with mile-high waves, followed by a sky so clogged with aerosols and debris that sunlight could not penetrate the atmosphere and photosynthesis shutdown. Food webs collapsed from the bottom up.
In his 2017 book, “The Ends of the Earth,” journalist Peter Brennan goes into even greater detail about this event, formally called the End-Cretaceous Extinction, which is the most recent of the five mass extinction events over the course of Earth’s 4.5-billion-year history. He also details the other four events, which occurred 445, 374, 252, and 201 million years ago, respectively. Remarkably, the End-Cretaceous Extinction was not the worst. That honor goes to the End-Permian Extinction, 252 million years ago.
To understand mass extinctions—defined as roughly 75% of all species going extinct over a few thousand to a few million years—it is helpful to understand the almighty carbon cycle, which sounds terribly exciting, I know. However, it is not a fool’s errand; the carbon cycle, though we seem hesitant to acknowledge it, is the key to our own existence, or lack thereof.
As an as-of-yet unchallenged tenet of science in the current milieu of science denial, the law of conservation of mass still abides. It simply states that whatever we started with we still have. The Earth was created with a certain amount of carbon, oxygen, nitrogen, and a slew of other elements. The amount of carbon, for instance, may change venues and forms over time, but the amount of it never strays from what we were given in the Big Bang. The same law holds for all mass. No one has ever found an exception.
The carbon cycle simply details the way carbon obeys the law of mass conservation, moving back and forth between our atmosphere and oceans and land (all of which was, at one point in history, covered by water). It is one big chemical equilibrium at play.
Carbon exists in our atmosphere as CO2, a gas, which acts like a one-way filter in the sky: letting sunlight in but blocking heat that is radiated from Earth back toward space. When it rains, water reacts with CO2 to make slightly acidic rain. Over great amounts of time—upwards of 100,000 years—exposed rocks are worn down by the rainfall, sending carbon and rock minerals (a lot of silicates and calcium) into the oceans. Sponges, corals, plankton and other ocean creatures then incorporate these minerals and carbon into their bodies. When they die and fall to the floor of the oceans, all that carbon is sequestered there as limestone (calcium carbonate).
Luckily, that is only half of the process. Carbon also makes its way back up into the atmosphere by way of volcanic eruptions, sea floor vents, and the natural circulation of ocean currents.
Left alone, this process is self-regulating. If CO2 builds up in the atmosphere, the climate and oceans warm, generating stormier weather and greater volumes of acidic rain, which in turn increases rock weathering. With more rock weathering, carbon is drawn down out of the atmosphere and the world cools down. It’s a giant thermostat, albeit a slow moving one.
Mass extinctions occur when this process gets out of whack. Too much carbon in the atmosphere and our world becomes an Easy Bake Oven; too little and we have an ice age.
Perhaps the most out-of-whack the cycle has ever been was during the End Permian Extinction (252 million years ago), also known as “The Great Dying.” It was the closest the earth has come to losing all land and marine life (90%). And while there were many culprits for the widespread extinction of species, a massive injection of carbon into the atmosphere was the prime driver of the event. Catastrophic volcanic eruptions, known as the Siberian Traps, blanketed millions of square miles of Siberia miles deep with magma, smothering life. But more deadly, the CO2 and methane released was so great that it is estimated that land temperatures soared to approximately 140 F, and ocean temperatures were closer to those of hot tubs (104 F) than oceans as we know them. If that weren’t enough, the acidification of the water would have been a final fatal blow.
When CO2 washes into the oceans, it mixes with the water and, again, forms a weak acid. Generally, all sorts of minerals—silicates and carbonates—and elements like calcium, through rock weathering wash into the oceans, too, buffering that acidification. However, if carbon is injected into the system faster than rock weathering (which is on the timescale of thousands of years)—as would be the case with volcanic eruptions, or rampant burning of fossil fuels—then the acidity increases unchecked and corals, plankton and other key marine species die, weakening and breaking the foundational food webs of the oceans.
The good news about mass extinctions is that unless they are 100% (in which case we would have a dead planet, forevermore,) something always comes back. The fall of the dinosaurs, in fact, cleared the way for us diminutive mammals to evolve and eventually reign over the Earth. It just takes a while; 66 million years in that case.
So, what does all of this have to do with us? Does the distant past provide our prologue?
If nothing else, we should realize that if we mess with the carbon cycle too much—which we are doing—it will mess with us. And, as the dinosaurs can attest to in their fossil record, it won’t end well.
How are we messing with the carbon cycle?
In a miniscule amount of time as geochemistry goes, we are releasing massive amounts of carbon into the atmosphere faster than the world can equilibrate. By burning up rain forests, by burning up, literally, eons worth of fossil fuels so rapidly, we are throwing the giant chemical equilibrium out of balance. As Brannen points out in “The Ends of the World,” we are currently releasing 40 gigatons of CO2 into the atmosphere every year, the fastest rate in the last 300 million years, a time span that includes two mass extinctions driven by a CO2 imbalance.
The glass half empty people will say, “We’re all going to die anyway, what does it matter if we burn it all up?”
It’s true, if we precipitate the end of the world by dumping carbon into the atmosphere all of us will be long gone when the heat goes up and the waters rise. But maybe it’s time to look beyond our own glass of water.
It took 3 billion years for multi-cellular life to even take hold on a planet blessed with the Goldilocks conditions for life. That seems a rare combination of remarkable perseverance and fantastic luck. Even if it doesn’t benefit us—or anyone that follows us—that seems worthy of marvel, and even reverence.