Today's Reading

We know the ecological murder weapon behind this Cretaceous case study. An asteroid or similar body of space rock some seven miles across slammed into Earth, leaving a geologic wound over fifty miles in diameter. Most species from the Cretaceous disappeared in the aftermath. It's difficult to stress the point strongly enough. The loss of the dinosaurs was just the tip of the ecological iceberg. Virtually no environment was left untouched by the extinction, an event so severe that the oceans themselves almost reverted to a soup of single-celled organisms.

We are fearfully enraptured with the idea of such terrible devastation. When the impact at the end of the Cretaceous was scientifically confirmed, news of the disaster inspired not one but two blockbuster films about planet- killing asteroids in the summer of 1998. That such a huge rock could kill more than half of Earth's known species suddenly seemed as obvious as the lethality of a gunshot. Simply knowing the terrible consequences of this disaster has been enough for us to look at the night sky with continued suspicion. If it happened before, it may happen again. NASA keeps an eye on the sky through their Sentry program, hoping to identify threatening asteroids and comets before they get too near.

But we often forget the unusual nature of the K-Pg crisis. Experts have often spoken of the calamity as part of the Big Five—a quintet of mass extinctions that have radically altered life's history. The first extinction crisis, between 455 to 430 million years ago, reshaped the oceans, erasing entire families of archaic invertebrate weirdos and allowing fish to thrive. Rapid global cooling and plummeting sea levels killed about 85 percent of known marine species, reshuffling the evolutionary deck. The second event, spanning 376 to 360 million years ago, shook life up once more. Precisely what caused the disaster is unknown—a drop in ocean oxygen levels is suspected—but the sudden change killed about half of known creatures, reducing the diversity among organisms like trilobites and corals that formed the basis of ancient reefs.

Worse still was the third, peaking about 252 million years ago. This was the Great Dying, fueled by incomprehensibly violent and sustained volcanic activity that wiped out about 70 percent of known species on both land and sea through climate and atmospheric changes. Our protomammal ancestors, who had held sway in terrestrial ecosystems, were almost entirely extinguished. Their downfall is what allowed reptiles, including dinosaurs, to stage their evolutionary coup. Following that, about 201 million years ago, another disaster killed off a great number of the crocodile relatives that ruled the land and gave dinosaurs their shot at dominance. Once again, intense eruptions were to blame. Greenhouse gases belched into the atmosphere, spurring a burst of global warming followed by intense global cooling. Atmospheric oxygen levels dropped, the seas became more acidic, and the drastic shifts between too hot and too cold were too much for many species to cope with.

But none of these catastrophes were quite like the extinction event that ended the Mesozoic. These previous apocalypses took place over hundreds of thousands or even millions of years, with phenomena like intense volcanic activity and climate change creating grinding, protracted transformations that shifted the makeup of life on Earth over long time spans. The causes of death were also highly variable—ocean acidification prevented shell-building creatures from constructing their calcium carbonate homes, for example, while decreased atmospheric oxygen might have slowly choked terrestrial organisms. What happened at the close of the Cretaceous, however, had global reach. And it happened fast.

The happenstances that triggered the Late Cretaceous extinction culminated in one terrible instant, a rare sliver of time that we can pinpoint as the very moment that life would never be the same. Before the strike, thousands of species flourished on every continent. There were so many varieties of dinosaurs and assorted other creatures that paleontologists are still clocking overtime to find them all, with new toothy, sharp-clawed wonders being named every year. Experts even expect that there were scores of species we'll never know as they lived in places where the circumstances of deposition and sedimentation did not allow them to be preserved, such as dinosaurs that lived in the mountains or other environments that were eroded rather than laid down as layers in stone. Mesozoic life was at its peak. Then, almost overnight, the dinosaurs were all but extinct and the planet's ecosystems were in disarray. This was the worst single day in the history of life on Earth, followed by tens of thousands of years of struggle for the survivors.

Our view of the K-Pg extinction has been hard-won. In fact, the task has involved overcoming our greatest weakness—human hubris. When the famously cantankerous British anatomist Richard Owen coined the name "Dinosauria" in 1842, the great reptiles weren't all that much of a mystery.

At the time, only three were known to scientists and the scaly trio seemed to mark part of life's expected progression. Geologists had identified an Age of Fishes, an Age of Reptiles, and an Age of Mammals, moving from low, squishy, squiggling forms of life through scaly monstrosities who were little more than a paleontological sideshow before mammals took up their starring roles. Whether understood as part of a creator's plan or evolution's great march, dinosaurs fit into a world of progress and refinement. No one needed to ask why they went extinct. How could shambling, malformed monsters that looked like a herpetologist's nightmare ever be the pinnacle of life's story? Great catastrophes turned over the makeup of life on Earth, but there was always a sense that the extinct species deserved their fate. That in some way or another, they were simply practice for what was to come.

...

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Today's Reading

We know the ecological murder weapon behind this Cretaceous case study. An asteroid or similar body of space rock some seven miles across slammed into Earth, leaving a geologic wound over fifty miles in diameter. Most species from the Cretaceous disappeared in the aftermath. It's difficult to stress the point strongly enough. The loss of the dinosaurs was just the tip of the ecological iceberg. Virtually no environment was left untouched by the extinction, an event so severe that the oceans themselves almost reverted to a soup of single-celled organisms.

We are fearfully enraptured with the idea of such terrible devastation. When the impact at the end of the Cretaceous was scientifically confirmed, news of the disaster inspired not one but two blockbuster films about planet- killing asteroids in the summer of 1998. That such a huge rock could kill more than half of Earth's known species suddenly seemed as obvious as the lethality of a gunshot. Simply knowing the terrible consequences of this disaster has been enough for us to look at the night sky with continued suspicion. If it happened before, it may happen again. NASA keeps an eye on the sky through their Sentry program, hoping to identify threatening asteroids and comets before they get too near.

But we often forget the unusual nature of the K-Pg crisis. Experts have often spoken of the calamity as part of the Big Five—a quintet of mass extinctions that have radically altered life's history. The first extinction crisis, between 455 to 430 million years ago, reshaped the oceans, erasing entire families of archaic invertebrate weirdos and allowing fish to thrive. Rapid global cooling and plummeting sea levels killed about 85 percent of known marine species, reshuffling the evolutionary deck. The second event, spanning 376 to 360 million years ago, shook life up once more. Precisely what caused the disaster is unknown—a drop in ocean oxygen levels is suspected—but the sudden change killed about half of known creatures, reducing the diversity among organisms like trilobites and corals that formed the basis of ancient reefs.

Worse still was the third, peaking about 252 million years ago. This was the Great Dying, fueled by incomprehensibly violent and sustained volcanic activity that wiped out about 70 percent of known species on both land and sea through climate and atmospheric changes. Our protomammal ancestors, who had held sway in terrestrial ecosystems, were almost entirely extinguished. Their downfall is what allowed reptiles, including dinosaurs, to stage their evolutionary coup. Following that, about 201 million years ago, another disaster killed off a great number of the crocodile relatives that ruled the land and gave dinosaurs their shot at dominance. Once again, intense eruptions were to blame. Greenhouse gases belched into the atmosphere, spurring a burst of global warming followed by intense global cooling. Atmospheric oxygen levels dropped, the seas became more acidic, and the drastic shifts between too hot and too cold were too much for many species to cope with.

But none of these catastrophes were quite like the extinction event that ended the Mesozoic. These previous apocalypses took place over hundreds of thousands or even millions of years, with phenomena like intense volcanic activity and climate change creating grinding, protracted transformations that shifted the makeup of life on Earth over long time spans. The causes of death were also highly variable—ocean acidification prevented shell-building creatures from constructing their calcium carbonate homes, for example, while decreased atmospheric oxygen might have slowly choked terrestrial organisms. What happened at the close of the Cretaceous, however, had global reach. And it happened fast.

The happenstances that triggered the Late Cretaceous extinction culminated in one terrible instant, a rare sliver of time that we can pinpoint as the very moment that life would never be the same. Before the strike, thousands of species flourished on every continent. There were so many varieties of dinosaurs and assorted other creatures that paleontologists are still clocking overtime to find them all, with new toothy, sharp-clawed wonders being named every year. Experts even expect that there were scores of species we'll never know as they lived in places where the circumstances of deposition and sedimentation did not allow them to be preserved, such as dinosaurs that lived in the mountains or other environments that were eroded rather than laid down as layers in stone. Mesozoic life was at its peak. Then, almost overnight, the dinosaurs were all but extinct and the planet's ecosystems were in disarray. This was the worst single day in the history of life on Earth, followed by tens of thousands of years of struggle for the survivors.

Our view of the K-Pg extinction has been hard-won. In fact, the task has involved overcoming our greatest weakness—human hubris. When the famously cantankerous British anatomist Richard Owen coined the name "Dinosauria" in 1842, the great reptiles weren't all that much of a mystery.

At the time, only three were known to scientists and the scaly trio seemed to mark part of life's expected progression. Geologists had identified an Age of Fishes, an Age of Reptiles, and an Age of Mammals, moving from low, squishy, squiggling forms of life through scaly monstrosities who were little more than a paleontological sideshow before mammals took up their starring roles. Whether understood as part of a creator's plan or evolution's great march, dinosaurs fit into a world of progress and refinement. No one needed to ask why they went extinct. How could shambling, malformed monsters that looked like a herpetologist's nightmare ever be the pinnacle of life's story? Great catastrophes turned over the makeup of life on Earth, but there was always a sense that the extinct species deserved their fate. That in some way or another, they were simply practice for what was to come.

...

Join the Library's Online Book Clubs and start receiving chapters from popular books in your daily email. Every day, Monday through Friday, we'll send you a portion of a book that takes only five minutes to read. Each Monday we begin a new book and by Friday you will have the chance to read 2 or 3 chapters, enough to know if it's a book you want to finish. You can read a wide variety of books including fiction, nonfiction, romance, business, teen and mystery books. Just give us your email address and five minutes a day, and we'll give you an exciting world of reading.

What our readers think...