Which of the following most accurately states the main point of the passage?
The worst day in the history of life on Earth, so far, happened almost exactly 66 million years ago, when an asteroid roughly the size of Manhattan slammed into the Yucatán Peninsula.
You may know the story. The asteroid—which arrived, probably, in June or July—immediately drilled a 20-mile hole into the planet’s surface, vaporizing bedrock and spewing it halfway to the moon. The planet shuddered with magnitude-12 earthquakes, loosing tsunamis across the Gulf of Mexico. Some of the ejected debris condensed in orbit and plunged back to Earth as searing spheres of molten glass, which torched the land and turned forests into firestorms. Other debris remained high in space, where it blocked the sun’s rays and began to chill the surface of the planet.
The impact changed the chemical content of the ocean, rendering seawater more acidic and inhospitable to the tiny plankton that form the base of the marine food chain. Combined with the other effects of the asteroid—darkened skies and a snap of global cooling—this ecologic disruption doomed much of life on Earth.
How does an asteroid prompt an extinction? It chooses the right location. The Yucatán Peninsula was an excellent one, says Pincelli Hull, an author of the paper and a geology professor at Yale. The peninsula is essentially an “old buried reef,” she told me, an accumulation of dead coral and other sea life that is now more than a mile thick. When the asteroid hit, untold megatons of that old organic material—rich in nitrogen and sulfur—instantly became dust and shot up into the atmosphere.
Soon it began to fall back down, now as nitric oxide and sulfuric acid. “It was raining brimstone and acid from the sky,” Hull said. The air would have reeked of acrid smog and burnt matches. The acid accumulated in the oceans, wearing away the shells of the small, delicate plankton that serve as the basis of the marine food chain. Within a few centuries of the impact, ocean acidity had jumped by at least 0.3 pH units.
This spike in ocean acidification may have lasted for less than 1,000 years. But even that pulse “was long enough to kill off entire ecosystems for sure,” Hull said. This pulse—called the K-T pulse—of ocean acidification also likely worsened other sweeping environmental changes wrought by the impact, such as the years-long darkness caused by orbiting debris and ash from the global wildfires.
With this new finding, it now appears that all three of the worst mass extinctions in Earth’s history featured huge spasms of ocean acidification. And that pattern is worrying, because the oceans are acidifying again today. Carbon dioxide—the same air pollutant that causes global warming—also dissolves in the oceans and increases the acidity of seawater. Since the late 1980s, the planet’s oceans have become about 0.02 pH units more acidic every decade, according to a report last month from the Intergovernmental Panel on Climate Change. More than a fifth of all modern carbon pollution has already dissolved into the oceans, the report also found.
Modern acidification is not yet at the same magnitude as the K-T pulse. It’s “moving toward that scale, but it’s not quite there yet,” Hull said. What unites our world and the K-T period, she said, is that a number of environmental catastrophes can overlap with ocean acidification to produce a major upheaval.
Source The asteroid that struck the Yucatan peninsula caused the oceans to become acidic and led to he worst mass extinction of life on Earth. Ocean acidification is occurring again today because of carbon dioxide emissions and this acidification is a cause for concern. The asteroid that hit the Yucatan peninsula nearly 60 million years ago would not have had such a terrible impact if it had landed elsewhere on earth. Our understanding of the mass extinction is changing thanks to new technology that tells us gives us greater insight into our planet's vast oceans. Researchers debate whether ocean acidification or other phenomenon were the main cause of the mass extinction that occurred 66 millions of years ago.