About 66 million years ago, life on Earth was brought to a halt by a catastrophic event when a 12 kilometers (7.5 mi) wide asteroid crashed into the ocean near Mexico’s Yucatan Peninsula.
The aftermath of this impact eventually wipes out three out of four plant and animal species worldwide, ending the dominance of that most famous group of creatures, the dinosaurs.
So how exactly did the dinosaurs die? Could an asteroid affect life to the same extent in the future?
Our modern world lacks the big, toothy, scaly animals that trample and roam the countryside. According to the fossil record, dinosaurs once occupied many ecological niches around the world.
The point in time when all this changed reflects the content of a distinct layer of sedimentary rocks called the Cretaceous-Paleogene (K-Pg) boundary.
The El Kef site in Tunisia is used to adequately represent the scale of this broad layer, although in fact a layer of compacted dust extends around the planet between 2 and 3 centimeters (about an inch) thick.
And under this rock? Lots of dinosaurs. On top of that, the closest creatures we can find to dinosaurs are the small, feathered varieties we call birds.
Although they are very thin, a few centimeters of sedimentary rock can pack material for tens of thousands of years. For decades, paleontologists have assumed that the extinction of dinosaur species occurred relatively gradually.
In the 1970s, American geologist Walter Alvarez was busy studying the chaotic formation of rock layers in the Italian mountains, layers that included the K-Pg boundary. To determine the actual time it takes for the layer to form, he turned to his father, physicist and Nobel laureate Luis Alvarez, who suggested measuring the amount of decay of the beryllium-10 isotope as a timer.
And that would be a good idea if it weren’t for the fact that all the beryllium matter has long since disappeared, leaving nothing of value to measure. Therefore, another element, iridium, was proposed as an alternative.
As is the case with many of the planet’s heaviest elements, much of the Earth’s iridium has sunk to its core over its history. Anything that has been found near the surface most likely arrived in a thin haze of dust that falls on our planet daily from interplanetary space.
Alvarez and his father predicted that iridium would be one in ten billion particles. And what they found was 30 times the concentration. Even more shocking is that this element is found in concentrated amounts in the same layer all over the planet.
And this explosion of iridium means more than the usual delicate dust of cosmic balls. A supernova can be ruled out because no trace of the plutonium-244 isotope has been found, other than a burst of iridium that left a surprising dose of space rock.
The 1980s were an exciting time for geologists, chemists and paleontologists seeking to piece together a scenario around the asteroid impact hypothesis.
Shortly after Alvarez and his father published their hypothesis, an oil company discovered traces of a 180 kilometers (110 mi) wide crater under the Yucatán River.
Today, few people discuss the fact that about 66 million years ago a large asteroid fell on our planet, and the time of this collision coincided with the mass extinction event. There is still debate about how exactly a medium-sized meteorite could cause such a carnage.
How did an asteroid impact lead to the extinction of many species?
The pallor of dust and smoke in the atmosphere will cause major changes in the global climate, altering temperatures and food chains in ways that will rapidly kill many species.
And there is a lot of evidence that the Earth was rocked by the K-Pg impact. “Tsunami waves” refers to the sheer force of the explosion. Chemical signs of a global phenomenon of particles blocking sunlight confirm the possibility of a planetary winter. There are even signs of drastic changes in the chemical composition of the ocean, which explain the mass death of marine life.
But are these changes, however vast, sufficient to explain the extent of the destruction? Sure, it was a big part of rock, but life proved surprisingly resilient in the face of big changes.
There is some argument that dinosaurs, especially the large ones, were particularly vulnerable to large-scale environmental change and may already have been on their way to extinction. A collision with an asteroid pushed him to the limit. This hypothesis is still highly debated, and the evidence is difficult to interpret in one way or another.
One of the hypotheses of recent years suggests that it is not the size, but the exact location of such an impact that really shakes the planet’s atmosphere. Even medium-sized chunks of rock from space can cause long periods of dangerous cooling if they enter a geological environment containing the right minerals.
Given the fact that the meteor could have hit at a critical angle, we may have good reason to believe that the same 12 km asteroid could have been less destructive if it had hit a few seconds later, in a slightly different place and on slightly different degree point. Which would make it less dangerous for the dinosaurs, but more a matter of awful timing for a few awful seconds.
Near-Earth asteroid monitoring programs tasked with providing us with information on potentially devastating impacts show that there is nothing to worry about in the near future.
Except for the rare case of a rock hidden in bright sunlight, or an asteroid pushed by gravity in ways that are difficult to predict, we seem to have plenty of time to come up with a plan.
However, given enough time, we can expect the Earth to experience a similar effect again. And if we can’t use technology to avoid impacts, we need to prepare for some kind of environmental impact.
Source: Science Alert
