Extinction’s Tipping Points

Week in Review / by Lee Billings /

How the extinction of the dinosaurs, Arctic methane leaks, and nuclear weaponry reveal the precarious thresholds of life on Earth.

Illustration: Mike Pick

Tipping points, as popularized by Malcolm Gladwell’s eponymous bestseller from 2000, are critical thresholds within a system where a small change or shift can snowball into a much larger one, rippling nonlinearly through the entire system and transforming it from one stable state into another. Examples include the boiling point of water, the spread of an idea (or a virus) within a population, and the slight shift in balance that can send someone from standing to sprawling across the floor. This week, several potential tipping points have made headlines. But unlike the relative triviality of brewing tea, catching a cold, or falling on one’s face, these critical thresholds concern the past and future of every living thing on Earth.

In the latest edition of Science, 41 researchers have attached their names to a paper summarizing and supporting the hypothesis that a massive asteroid slammed into our planet 65.5 million years ago and drove dinosaurs into extinction. This event brought an end to the Cretaceous period and ushered in the modern era of mammalian dominance; without it we would not be here.

There are several reasons to believe this is what happened, but two pieces of evidence are more crucial than the others. The first is a thin layer of rock found around the globe that is laden with iridium, an element rare on Earth but common in asteroids. This iridium-rich layer was announced in 1980. The second is the monstrous 180-kilometer-wide Chicxulub crater in the Yucatan Peninsula, which was linked in 1991 to the end-Cretaceous impact. The researchers reviewed data that has accrued in the intervening decades, and strengthened the correlation between Chicxulub, the iridium layer, and the extinctive aftermath.

The real revelation for most readers might be that the “impact” hypothesis for the dinosaurs’ extinction was even in question, since the theory has become embedded in public consciousness through years of news stories, textbooks, and cartoons. And while the evidence is overwhelming that an asteroid hit the Earth around 65.5 million years ago in what is now the Yucatan Peninsula, some notable critics believe the dinosaurs were already sliding toward extinction millions of years before this event from other pressures like massive volcanic eruptions or rampant virulent diseases, or that they persisted for hundreds of thousands of years after the impact. It seems extinction events could require a synergy of multiple as-yet-mysterious factors. Was the Chicxulub impact a tipping point for the dinosaurs?

The fact is, all five of the Earth’s known major mass extinctions lie so far in the geologic past that we may never know with utmost certainty their circumstances. The review paper in Science is, more than anything else, an attempt to push the impact theory past the tipping point of consensus, where questioning it will no longer be socially acceptable in scientific circles. After all, acknowledging that a rock from space had wiped out much of life on Earth in the past could prove helpful for future planning. It could happen again.

Another study from the same issue of Science shows that not all world-threatening tipping points are as obvious as a huge rock falling from the sky. An international team of scientists has conducted a five-year survey of the East Siberian Arctic Shelf, a stretch of seafloor more than two million square kilometers in size, finding that the Shelf is venting vast amounts of methane into the atmosphere. One potential cause is warming ocean waters, which are melting and destabilizing the seafloor permafrost that sequesters the methane.

Methane is a potent greenhouse gas, at least 30 times more effective at warming the Earth than the much-maligned carbon dioxide. At best, this is an old, ongoing phenomenon, requiring only a revision of global climate models to account for this newly discovered source of methane. At worst, the Siberian methane release is a recent development, and portends a looming climate tipping point of catastrophic proportions. More methane entering the atmosphere results in a warmer planet, and certainly a warmer Arctic, which melts more permafrost and releases even more methane. This positive feedback loop could turn the Siberian methane trickle into a torrent, abruptly raising average global temperatures and amplifying ongoing climate change. Some researchers believe such runaway methane outgassing was a tipping point for the world’s most severe mass extinction, the Permian-Triassic event of 251 million years ago, which wiped out an estimated 96 percent of marine species and 70 percent of land-based vertebrates. This event was so devastating even insects were driven to the brink of oblivion.

According to the futurist Jamais Cascio, another tipping point may lurk within the recent methane discovery: the acceptability of using “geoengineering” techniques in attempt to counteract rapid climate change. Cascio speculates that the worst-case scenario of runaway methane release from Siberia could effectively force the hands of nation-states (or even non-state actors) to deploy risky technologies like ocean fertilization, artificial volcanoes, or bioengineered bacteria capable of absorbing and sequestering excess atmospheric methane. The complexity of the Earth as a system ensures that the consequences of such actions would be difficult to predict and could result in disaster, but against the certainty of a rapidly warming world even desperate gambles would likely be pursued. On the other hand, some very reputable climate experts believe the latest Siberian methane findings aren’t that frightening.

While we’re speculating about grim man-made scenarios that seem, for now, in the realm of science fiction, it’s worth considering another nightmarish situation that we know is all too real: the continued threat of a nuclear holocaust. Despite the end of the Cold War decades ago, both the United States and Russia still maintain stockpiles of nuclear weaponry sufficient to destroy modern civilization many times over. And as more countries gain the necessary technological prowess to build such weapons, the “nuclear club” seems set to grow, increasing the risk of nuclear warfare and the proliferation of nuclear weapons to terrorist organizations. This dangerous situation was exacerbated by the last Bush administration, which balked at arms-control treaties, planned new nuclear armaments (including low-yield “tactical” weapons), and threatened nuclear preemption or reprisal to chemical or biological attacks on the US.

Perhaps this can change. In speeches last year in Prague and at the United Nations, President Obama pledged to pursue a world free of nuclear weapons, which probably helped secure him a Nobel Peace Prize. Now may be the tipping point for whether anyone can take that pledge seriously. This week, the President was slated to meet with senior officials to hash out the nation’s Nuclear Posture Review, a crucial activity for each incoming administration that guides the funding, deployment, regulation, and retirement of nuclear weapons. And though Obama said last week that the Review would reduce the role of nuclear weapons in US national security, it appears several revolutionary proposals have already been dismissed. According to reports from the Washington Post and the New York Times, Obama is unlikely to abandon the possibility of using nuclear weapons preemptively, and is under pressure to avoid unambiguously stating that deterrence is the sole role of US nuclear weapons. So much for a nuclear-free world.

Of course, realistically speaking, global nuclear disarmament will be a slow and methodical process at best. Nuclear weapons are unquestionably potent tools for international “negotiation.” This is probably why Iran announced last month that it was enriching its uranium beyond that required for nuclear reactors and approaching levels primarily suited for military purposes. This, too, may be a tipping point of sorts. As laid out in a thoughtful article this week by the New York Times’ William J. Broad, uranium refining is a nonlinear process where the rich get richer: Extracting a small percentage of volatile uranium-235 from the far more common and inert uranium-238 is a Herculean task, but once that is achieved, further enrichment is much easier. Weapons-grade uranium is now within Iran’s reach. How that will tip the world’s scales remains to be seen.

Lee Billings is a staff editor for Seed. He likes space.

Originally published March 12, 2010

Tags public perception resilience space systems

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