How Dinosaurs Really went Extinct!
None of us would have wanted to be around on Earth 66 million years ago.
First of all, the disposition of the continents was very different from today:
India was still a large island drifting between Africa and Antarctica, pushed by
tectonic forces towards the Asian subcontinent where millions of years later with its thrust
would have gone to form the Himalayan chain. Europe and the entire Mediterranean area were
still completely submerged and the Atlantic Ocean appeared as a narrow arm of sea between South
America and Africa, two continents that had been receding from each other for only a few million
years. The whole region of Central America and the central part of North America was still submerged.
Moreover, the whole planet was inhabited by dangerous, gigantic and wild creatures
from which it would have been better to keep away. A totally alien planet in the eyes of us naked
apes of the 21st century... But something, fortunately for us,
was about to change things forever.
On that day 66 million years ago, something became visible in the sky that was not there before:
a celestial body as bright as a star, which became brighter and brighter as time passed.
The beasts, all intent on grazing and hunting, probably did not ask questions,
nor could they know that it was an asteroid of almost ten kilometers in diameter,
headed towards their planet. The entry into the atmosphere of
this cosmic mountain larger than Everest produced a colossal shock wave, with a bang so strong that
millions of birds and pterosaurs flew around the world, scaring even the bravest T. Rex to death.
Then the great space rock reached the ground at an estimated speed of twenty kilometers per second,
vaporizing the waters of a shallow sea at what is now the Yucatán Peninsula in the Gulf of Mexico.
According to simulations and mathematical models made in recent years, the impact led
to the formation of a crater 180 kilometers in diameter, carved into the earth's crust to
a depth of twenty kilometers. All throwing into the atmosphere about 25 trillion tons of debris,
raising them up to 30 kilometers high. At the edge of the newly formed crater, a rocky crown
higher than the Himalayan chain rose and then collapsed in the space of only three minutes,
leaving a ring of crystalline basement in a geological formation called Peak ring.
Similarly, at the center of the crater, a rocky peak sputtered upward and then broke against
the ground again, with an effect similar to throwing a sugar cube into a cup of coffee.
Ten minutes later, the rocks stabilized and stopped behaving like a fluid mass.
The impact also caused earthquakes of unspeakable power and devastating tsunamis. Waves up to
1500 meters high spread in ever-widening circles away from the epicenter of the fall,
disrupting the water masses of the entire planet and carrying sediment up to 6000 km away
with waves tens of meters high that fell on the coasts. When the seas retreated,
brought with them vegetation, animals and debris from the hinterland, pouring on the seabed where
they are still found today, fossilized and submerged by other layers of rock.
The energy produced in the impact was equal to that of a billion atomic bombs similar
to the one dropped on Hiroshima. An infinite amount of incandescent material was projected
in a few moments beyond the atmosphere, and then fall back to Earth thousands of miles away.
Debris was so hot that it ignited everything it encountered in its fall towards the ground.
A huge cone of liquefied rock rose into the air, producing a gigantic hailstorm of small
glassy fragments, the "tektites", which would cover much of the western hemisphere.
Some of the debris projected beyond the atmosphere even managed to exceed the escape velocity,
projecting into space to probably reach other planets such as Mars and perhaps the moons of
Jupiter. Some of these fragments perhaps carried with them terrestrial bacteria,
making the asteroid that wiped out much of the life on Earth
an indirect distributor of life on other worlds far from ours.
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Meanwhile, Earth quickly became an inferno. Incandescent dust enveloped
much of the atmosphere, causing fires first in the western hemisphere and later
in Indian forests thousands of miles away from the Yucatán. The fires charred about 70
percent of all forests existing at the time. For months, perhaps years, the dust in the
atmosphere, together with soot from the fires, prevented the sun's rays from filtering through.
The processes of photosynthesis stopped almost completely,
leading to the end of most of the plants and causing a net reduction of oxygen in the air.
With the fires now extinguished, the Earth entered a dark and icy period; a condition that, together
with the direct consequences of the fall of the asteroid, contributed to the extinction of 75%
of the species that populated the Earth at that time... first the plants,
and then the animals. Not only did the dinosaurs disappear, but also the ichthyosaurs in the seas,
the pterosaurs in the skies and many other lesser-known animals, including many marine
invertebrates, such as ammonites with elegant spiral-wound shells. And all this in a relatively
short period, perhaps a few months, but that, according to some, lasted for a million years.
Perhaps even the vast majority of the population of the species that survived the extermination
died, but, being in this case of small and very fertile animals, they were able to
reproduce quickly and avoid total depopulation. Although it is not the only one of the great
extinctions in the history of the Earth, and not even the largest in terms of number of species
disappeared, the extinction of the end of the Cretaceous has fascinated generations of scholars
and amateurs because among the excellent victims of this event
there were the "great reptiles", the dinosaurs; although with them, as we have seen, thousands
of other species disappeared: vertebrates and invertebrates, marine and terrestrial.
At this point the question might be: but how do we know all this?
The answer is that for a long time paleontologists had already noticed an extraordinary fact: that in
the oldest geological layers of 66 million years, there were plenty of fossils of all kinds, while
in the layer immediately above, the youngest of 66 million years, you could see the almost complete
disappearance of any type of fossil remains ... This discontinuity was called "K-T Boundary"
because it marks the dividing line between the Cretaceous period (K) and the Tertiary period
(T). In practice, digging immediately below the K-T we find traces of the Cretaceous period,
while if we dig immediately above we find those of the Tertiary period, where the remains of
dinosaurs mysteriously disappear almost suddenly. To explain this absence, they first resorted to
the strangest theories, invoking universal floods, epidemics, climate change,
the reversal of the magnetic poles and much more. Then, for decades, researchers believed that
the extinction had occurred in a much more gradual way than the K-T layer could suggest.
In fact, they blamed the great volcanic activity and climate change that made the planet less and
less suitable for life of dinosaurs and many other forms of life, leading to extinction.
At the end of the seventies, Walter and Luis Alvarez (father and son,
the first a Nobel prize physicist, the second, a geologist) came to a different conclusion:
they found that in the famous K-T Boundary there was an unusual concentration of iridium, that in
that amount could only be of extraterrestrial origin. In 1980 Alvarez published their study,
hypothesizing that iridium was deposited all over the Earth surface after the fall of a
large asteroid, able to extinguish most of life on Earth. The fact that the iridium was right in
the K-T transition zone between Cretaceous and Tertiary was, according to Alvarez,
the decisive proof of a catastrophic event responsible for such a large mass extinction.
The theory was immediately successful, however, the "smoking gun" was missing.
Where was the crater that the fall of an asteroid at least 10 km in diameter must have
dug on the surface of the earth? Certainly, it could hide in the depths of the ocean,
but the fact that it was not found contributed to feed the dissent of those who still
supported an extinction occurred on a longer time and because of volcanism.
All this until 1991, when it was announced the discovery of a submerged crater in the
Yucatán peninsula, which for age (66 million years), size
(180 km) and chemical composition, was fully compatible with the asteroid theory.
The crater was then named Chicxulub, after the nearby locality of the same name.
The discovery led to further investigation and analysis, resulting in the publication of
a research in Science in 2010 where more than forty researchers from different disciplines
came to a shared conclusion: it was the impact of an asteroid to cause the mass
extinction of 66 million years ago, the diatribe had to be considered resolved.
A minority of researchers, however, continued to believe that the extinction occurred
gradually due to climate change caused by the great volcanic activity at the time, which lasted
for hundreds of thousands of years. But without denying the impact of an asteroid, which came
to give the final blow when the extinction of the dinosaurs had already begun for some time.
But then, between asteroid and eruptions, who was the real culprit of the mass extinction
that led to the disappearance of almost all marine and continental species existing on Earth,
including dinosaurs? A recent study would seem to
partially exonerate volcanic eruptions, thanks to results obtained through computer
simulation models of complex global phenomena. Using models that relate the circulation of the
atmosphere with that of the waters of the oceans, in association with the reconstruction of the
habitats in which dinosaurs lived, scientists have brought new data to support the hypothesis
that only the impact with an asteroid could have caused a solar darkening such as to precipitate
the globe in a planetary winter with a fall in temperatures up to 60 ° C and to destroy the
ecological space of habitability of the dinosaurs. The asteroid would then be the main culprit of
the extinction of the dinosaurs, while volcanic eruptions would have played only a secondary role.
In short, at the moment we can safely say that an unspecified day of 66 million years ago,
the region we know today as Yucatan was hit by an object of about 10 km in diameter.
An asteroid, coming from the northeast at a speed of 20 km per second,
impacted the open sea at an angle of about 60 ° from the horizon.
This made the impact catastrophic. If the body fell from space had arrived more vertically,
it would have dragged with it to the depths of the crust the pulverized rocks, without
releasing debris and dust into the atmosphere; if it had been less vertical, however, would not have
broken through the Earth's crust, reducing the release of magma, gas and dust from the depths.
All this made the Earth - a planet so suitable for life and a formidable
exception in the history of the Solar System - a dark and inhospitable place for very long years,
hostile to most living things. When the first rays of sunlight
were able to filter through again, they illuminated great uninhabited plains,
forestless and ash-covered, and oceans essentially devoid of life. In that desolation, fungi and
algae shared their existence with a few other living things, such as small mammals and ferns.
Over millions of years, things improved, the climate returned to differentiation, and new
species evolved to populate the Earth once again. As long as there were dinosaurs, mammals had
no room to thrive and become dominant. Free from their presence and with an increasingly
prosperous planet at their disposal, they could finally thrive and begin the long road that
led to the birth of the first hominids and finally Homo sapiens, our species.
It is probably thanks to that asteroid, to the devastation that it brought to the planet millions
of years ago, if today you are in front of a screen listening to what is basically our story.