Researchers from the University of Edinburgh say the dinosaurs might have survived the asteroid strike that wiped them out had it happened slightly later or earlier in history.
Though many theories have been presented over the years to explain how and why the dinosaurs became extinct, a consensus is growing around the idea that it was a confluence of factors, with the massive asteroid strike serving as the final coup de grâce. This new study further affirms this notion, showing that by the time the six mile-wide (10-km) asteroid landed in what is now Mexico, the Earth's climate and environment were already in upheaval. It was the proverbial straw that broke the camel's back — the apex to a perfect storm of factors that ultimately led to the demise of a reptilian clade that dominated the planet for 135 million years.
An international team of paleontologists led by the University of Edinburgh reached this conclusion after reviewing updated fossil records (mostly from North America) and through the use of new analytical tools. Their new timeline paints a grim picture of what the dinosaurs were already dealing with in the few million years prior to the fatal impact.
The Edinburgh scientists say the Earth was experiencing extensive volcanic activity, changing sea levels, and significant fluctuations in temperature. This severely disrupted the ecosystem, resulting in a weakened food chain characterized by a lack of diversity among the large plant-eating dinosaurs on which others preyed.
According to study co-author Steve Brusatte, this decline made those ecosystems at the latter part of the Cretaceous Period considerably more vulnerable to collapse than those ecosystems that existed even a few million years before. He says there's good reason to believe that if the asteroid had hit a few million years earlier dinosaurs would have been better able to cope.
"The dinosaurs were victims of colossal bad luck," noted Brusatte in a statement. "Not only did a giant asteroid strike, but it happened at the worst possible time, when their ecosystems were vulnerable."
Needless to say, the asteroid strike was more than just the 'last straw' — it was more like the last anvil. The impact caused tsunamis, earthquakes, wildfires, sudden temperature swings, and other environmental changes. Material thrown into the air would have fallen as acid rain, while also blocking the sun's warmth. The planet would have cooled appreciably, perhaps by tens of degrees Celsius. Plants and other photosynthesizing organisms would have suffered terribly owing to an atmosphere suffused with dust.
By the time the cataclysmic dust had settled, some 80% of the Earth's species were gone. The food chains collapsed, wiping out the dinosaur kingdom one species after another. Today, the only extant remnants are birds, creatures who likely survived owing to flight and their compact shape.
"The great dinosaur mass extinction has been one of the world's biggest mysteries and has captured the imaginations of many people," noted study co-author Paul Barrett in The Guardian. "Although some types of dinosaurs were already declining in numbers before the famous asteroid impact, in most cases this impact was the smoking gun for the cause of the extinction. This new work provides the best evidence for sudden dinosaur extinction and for tying this event to the asteroid impact rather than other possible causes such as the longer-term effects of the extensive volcanic activity that occurred at the end of the cretaceous."
Fascinatingly, the researches surmise that if the asteroid had landed a few million years earlier, when the range of dinosaur species was more diverse and food chains more robust, or even later when new species had time to adapt to the changing conditions, then they very likely would have survived. As a result, however, humans would have most assuredly not emerged. The mass extinction paved the way for other animals to gain ground and occupy vacant environmental niches.
This study is set to appear in an upcoming edition of Biological Reviews.
Top image: Kerem Beyit.