This book, subtitled “The Astounding Interconnectedness of the Universe” sets out to explicate “our current knowledge about the Universe, the Milky Way, the Solar System, as well as what makes for a habitable zone and life on Earth.”
The author, an award-winning professor of science at Harvard, explains that there were five major mass extinctions in the past 540 million years, as well as about twenty lesser ones, in which approximately 20 percent of life-forms died out. Many people are familiar with the extinction of the dinosaurs, the Mesozoic species that dominated the planet for more than 100 million years. She reviews the observations of geologists and paleontologists confirming that a big object hit the Earth 66 million years ago and as a result at least 75 percent of life on the Earth died, including the dinosaurs.
The description of how scientists solved the mystery of the dinosaur extinction is fascinating. It included detecting huge amounts of the rare metal iridium in the clay of the K-Pg geologic boundary marking the period of the dinosaur extinction. The K-Pg clay layer was meticulously studied in almost 40 locations around the globe. Other rare metals in that clay layer were also found, at levels a thousand times higher than seen elsewhere on earth. Scientists also identified shocked quartz, which indicates a high-pressure origin, and crystals called spinels that point to rapid solidification after high-temperature melting. The only known sources for the state of these materials are meteoroid impacts and nuclear explosions. Obviously, there were no nuclear explosions before 1945, leaving only one “culprit” to account for the measurements.
Scientists, further investigating evidence left by the meteor impact crater at Chicxulub (pronounced CHICK-shuh-lube) in the Yucatán Peninsula in Mexico, concluded that the meteor had to have been an incredible 10-15 kilometers in diameter. An object the size and speed of that meteor “would have released an energy equivalent of up to 100 trillion tons of TNT, more than a billion times greater than that of the atom bombs that destroyed Hiroshima and Nagasaki.”
Even just a kilometer-wide meteoroid, the author points out, would do global damage, creating extreme winds, huge tsunamis, tidal waves, massive earthquakes, and trillions of tons of material ejected into the atmosphere and then rained down upon the Earth.
The only survivors would have been living creatures that could hide – through hibernation or otherwise.
The author suggests that a disk of dark matter might have been the trigger dislodging a comet from its orbit – probably in the Oort Cloud, and send it veering toward the Earth. A meteor from the comet then caused all this devastation upon impact.
In order to establish her theory, she has to take a detour to explain the composition and history of the Universe to readers. Thus she educates us about ordinary matter and how it differs from dark matter, and how we know about the existence of dark matter and dark energy. She talks about the composition of our Solar System, and how it operates within the Milky Way. She does all of this clearly and lucidly, with plenty of popular culture references and metaphors so that any reader should have no problem understanding her.
Although most of the book concerns impacts from meteoroids, the author ends with a cautionary note about a possible sixth extinction unrelated to celestial bodies:
“Many scientists today think we are currently undergoing a sixth mass extinction – of manmade origin. . . . The mammal extinction rate of the last 500 years has been about 16 times higher than normal, and in the last century the rate has been elevated by a factor of 32. Amphibians in the last century have died off at a rate nearly 100 times higher than in the past, with 41 percent currently facing the threat of extinction, while bird extinctions in this same time frame have exceeded the average rate by a factor of about 20. . . . The changes in the environment that are occurring now . . . have a disturbing resemblance to those at the time of the P-Tr extinction. [The P-Tr extinction was an event about 250 million years ago that was the most devastating known extinction in terms of the percentage of species that disappeared from the planet. While the cause of the P-Tr extinction remains the subject of controversy, massive climate change and changes in the chemistry of the atmosphere and oceans are thought to have been determinative.]”
“Incredibly, the rate of temperature and changes in pH (which measures acidity) seems to have been comparable at that time [the P-Tr extinction] to what they are today. Human influence is almost certainly largely to blame for the recent diversity loss. . . . We are very rapidly undoing the cosmic work of millions or even billions of years.”
Evaluation: The relationship between the dinosaur extinction and the presence of dark matter unfolds like a murder mystery. It was fascinating to read about how scientists pieced together clues and evidence to solve a “cold case” – one that occurred some 66 million years in the past.
Published by Ecco, an imprint of HarperCollins, 2015