Thursday, April 11, 2019

The extinction of the dinosaurs

Since their discovery, at the beginning of the 19th century, dinosaurs have always awakened human imagination. The past existence of such large animals, which seemed to have left no trace in the current fauna, is quite suggestive. In the multitudinous field of science, dinosaurs have always occupied an extremely attractive place. Dinosaurs have appeal.
On the other hand, the mystery of the disappearance of dinosaurs was soon posited. What could have caused their extinction? In the next century and a half, various possible causes were proposed, such as the following:
  • It was said, for example, that primitive mammals could have caused the extinction of dinosaurs by eating their eggs. The trouble is, both groups of animals lived together for a hundred million years without any problem. In fact, mammals were cornered by their giant neighbors and could not develop and spread until they disappeared.
  • It was also said that the apparition of flowering plants (Angiosperms) during the Cretaceous period, the last when dinosaurs lived, could have caused their extinction by a change in their diet. The trouble is, the Cretaceous period was very long, and flowering plants appeared thirty million years before the extinction of the dinosaurs. If they could put up with that diet for so long, why should it suddenly be fatal for them?
  • Another reason adduced was a change of climate. During the Mesozoic Era (the age of the dinosaurs) the Earth's climate was quite warm. Then, in the Tertiary period, it was colder. The bad news is that climate changes are usually gradual, while the disappearance of dinosaurs does seem to have been quite fast. Therefore it was proposed that the cause of the extinction could have been a sudden catastrophe that would have caused a sudden climate change.
Chicxulub crater
In 1980, a team led by Luis Álvarez, Nobel Prize in Physics, and his son Walter Álvarez, discovered that the sediments of the Mesozoic Era are separated from those of the Tertiary period by a narrow layer, where the iridium element abounds. That led the two scientists to propose that, 65 million years ago, an asteroid or a comet about 10 km in diameter would have crashed with the Earth, making the atmosphere saturated with dust, which would impede for a long time the arrival of the solar rays to the surface, causing the death of plants, of herbivorous animals, and consequently of carnivores. But while plants would resist in the form of seeds, and small animals (such as primitive mammals) would find enough food to survive, large animals, such as dinosaurs, would have become extinct. The discovery in 1990 of the Chicxulub crater in the Yucatan Peninsula, produced by an enormous extraterrestrial impact 65 million years ago, seemed to give final backing to this theory.
As often happens in science, alternative hypotheses did not disappear altogether. The catastrophe that caused the extinction could have another origin. Around the same time (about 65 million years ago) a huge volcanic activity took place in the Deccan, in India, which could have produced the same effects as the impact of a meteorite (saturation of the atmosphere by ejected dust). Since the two phenomena were almost simultaneous, the following dilemma was posed:
What came first, the impact of the asteroid (or comet) or the volcanic activity?
If the impact of the asteroid was earlier, volcanism could have been caused by it, along with the extinction of dinosaurs and many other living beings. But if the eruptions took place before the impact, perhaps this had no effect, because the dinosaurs would have become extinct before the extraterrestrial projectile arrived.
Two recent studies conducted in India by two independent scientific teams have tried to decide the issue using different dating methods using radioactive decay. The bad news is that the results they have obtained are contradictory. For one of the teams, the eruptions took place just before the impact; for the other, right after. The problem, therefore, remains unsolved.
Let us see how a serious popular science magazine (Science News) headlines this piece of news:
As usual, some mass media have not been able to resist the temptation to give the news a much more appealing headline, even at the cost of saying exactly the opposite. But we know that the media are more concerned about sales, and attracting their advertisers, than for the truth. Let us look at the headline for this news in the major Spanish newspaper El País:
By the way, I also addressed this issue in one of my science fiction novels, The Last Dinosaur, where I offered a third possible explanation for the extinction of dinosaurs, alternative to the two explanations currently considered most likely.

The same post in Spanish
Thematic thread on Primitive Life: Preceding Next
Manuel Alfonseca

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