From here on, we enter the realm of suppositions.
The proposed scenario is therefore only a possibility and does not
correspond to immutable scientific truth about the impact of the asteroid hitting the earth.
It is based on the previous conclusions and in particular on the
probable preponderant role of the impact of a celestial object in the
extinctions.
However, you will see that this scenario is able to explain almost all
the extinctions already highlighted.
As well as the selective
character of extinctions.
Scientists working on the reconstruction of the events have found it impossible
to proceed by analogy.
Since no other examples of impact events of comparable magnitude are
known.
Impact models of small objects
give some indication of environmental effects, but extrapolations to objects of
several kilometers in diameter are uncertain.
Asteroid impact according to its diameter
The devastating effects of an impact obviously increase with the
diameter of the asteroid and estimates are as follows…:
- From 1 to 9 meters in diameter (collision frequency = on average 1 per year): local damage.
- From 10 to 100 meters (1 every 100 to 10,000 years): damage on a regional scale, with a large crater.
- From 100 meters to 1 kilometer (1 every 10.000 to 100.000 years) …: damage on the scale of a continent, thus theoretically traceable over geological time.
A scenario of the catastrophe on earth
The celestial object that hit the Earth 65 million years ago was even
bigger, since it probably measured 10 kilometers in diameter.
Collision frequency: 1 every 100 million years?...
The catastrophe must have unfolded according to the following events.
According to a proposed scenario for the collision of an asteroid of 10
kilometers in diameter:
- The energy released during the impact (5 billion times that of the Hiroshima bomb) raises the temperature by 10,000 or 20,000°C.
- The shock causes an earthquake of magnitude 12, with important sedimentary displacements (turbidites) as well as a resumption of volcanic and hydrothermal activities.
- By comparison, the most violent earthquake ever recorded by man had a magnitude of only about 9.
- An earthquake of magnitude 12 is millions of times more powerful and cannot be caused by the tectonic activity of the Earth alone.
- The rocks from the asteroid and the excavation in the earth's crust vaporize, forming a gigantic "fireball".
- Knowing that the crater is generally twenty times the size of the bolide, we understand the importance of the volumes mobilized.
- The vaporized mass of the asteroid represents less than 1% of the total mass ejected.
- Part of the dust formed, including microspherules, spreads out in a carpet around the impact site.
- The rest (including iridium-rich particles) rises into the hole in the atmosphere created by the fall itself, whose speed reaches about 20 km/s.
- At an altitude of about 20 km, i.e. in the stratosphere, the cloud spreads and surrounds the Earth for several months.
- Before slowly falling back to the surface of the planet, where it forms the iridium-enriched layer.
- During this time, with the particles resulting from the combustions (in particular aerosols).
- This cloud stops the solar rays in a significant way, plunging the globe in the darkness and installing an impact winter.
- At the same time, the temperature is decreasing, more rapidly at the surface of the continents, with a difference of 40°C.
- The organisms of the high latitudes and those of the deep sea are logically less affected than those whose needs require light and heat.
The first event causing rock melting, vaporization, and forest fires over
huge areas.
The heat released into the atmosphere causes oxygen and nitrogen in the
air to combine.
The resulting NO2 falls as nitric acid rain, which is harmful to plants
and marine invertebrates.
This mobilization of O2 also results in a drop in ozone levels, allowing
increased passage of ultraviolet radiation.
But the impact of the K-T crisis took place at the edge of a continent,
on the continental shelf.
The asteroid arrived apparently in a shallow sea, thus provoking in
addition the formation of a huge tsunami propagating.
With a wave as high as the depth of the marine environment encountered,
about a hundred meters, and at a speed of 0.5 km/s.
This colossal tidal wave swept the coasts of southern North America and
Central America, hence the deposition of tsunamites in these regions.
In a radius of several thousand kilometers, the immediate devastation
must have been total.
It is therefore impossible to find fossils of animals contemporary with
the crisis.
In addition to the previous dust, enormous volume of water vapor is
propelled into the atmosphere causing a strong increase in the greenhouse
effect.
Because it absorbs many wavelengths of infrared rays emitted by the
Earth.
As this water vapor remains in suspension longer than the dust, a
significant warming follows the impact winter, creating a kind of
"Scottish shower".
A greenhouse effect also reinforced by the release of large quantities
of CO2 and SO2, projected in a few minutes.
The biological consequences
Although the direct effects of the Yucatan impact may have been
spectacular.
It is the consequences on a global scale that must have been responsible
for the extinctions.
The main role in the catastrophe is undoubtedly due to the enormous
quantity of dust and aerosols injected into the atmosphere by the collision.
The biological consequences of the impact night probably began with the rupture
of numerous food chains.
That had as their starting point the living photosynthetic plants, a
scenario popularized by the French paleontologist Eric Buffetaut.
Essential to plant life, photosynthesis cannot take place without light.
In the dark conditions that followed the impact, there must have been a
general decline of the plant world.
This in turn caused a chain reaction that severely affected the animal
species that drew their food from it.:
In the seas, the plant plankton "phytoplankton" was the first
to be affected by the lack of light.
And its near disappearance led to the breakup of a food chain that included
then the animal plankton.
Then invertebrates such as ammonites and belemnites, various types of
fish and finally.
At the end of the chain, the large marine reptiles such as plesiosaurs
and mosasaurs.
Beings that lived on the bottom and fed on organic matter buried in the
mud.
Such as certain burrowing mollusks, therefore resisted the disaster
better, because they did not depend directly on phytoplankton.
They were also animals that lived in fresh water and were part of a food
chain.
That started with particles of organic matter suspended in the water,
consumed by small invertebrates such as worms and crustaceans.
Which in turn were eaten by fish, which in turn served as prey to
aquatic turtles and crocodiles.
All these animals survived the Cretaceous-Tertiary crisis without much
damage;
On the continents, the vegetation was devastated and the large
herbivores, which needed large quantities of fresh plants to survive.
Especially the herbivorous dinosaurs,
disappeared for lack of food.
The break in this food chain led to the disappearance of the carnivorous
dinosaurs, deprived of their prey.
In this hypothesis, the extinction of the dinosaurs is thus reduced to a
temporary disappearance of food resources due to the darkness.
Those that were able to survive belonged to other food chains, not directly
involving living plants.
Which allowed them to survive during the period of darkness. They were
only small animals: small vertebrates such as lizards and small mammals.
Which fed on insects and worms and consumed the organic matter contained
in the humus and soil.
Thus, after several months, when the atmospheric dust was dispersed, and
sunlight was able to return to the surface of the Earth.
Most of the plants were able to develop thanks to the seeds, spores,
rhizomes, bulbs...
Which had been able to survive during the period of darkness, but for
the numerous animal species that had disappeared for lack of food.
That is to say nearly 70% of living species, it was too late.
Alert: the asteroid will hit the Earth!
Over the months, the probability that the asteroid will hit the Earth
has increased to 10%... then to 100%.!
That's when Nasa decided to send a probe in 2021 to observe it closely.
And in December 2021, astronomers are formal.:
The asteroid is heading straight for the region of Denver, Colorado
(United States), which it should wipe off the map.
To respond to the threat, the major space powers decided to build six
"impactor" ships to hit the asteroid and deflect it from its path.
The major space powers are: United States, Europe, Russia, China and
Japan.
But the manufacture takes time, it is necessary to coordinate the orbits
and the impacts are planned only in August 2024.
Finally, three impactors manage to reach the target and break it. Is this
good news..? Yes, because the threat of a regional disaster is averted.
But unfortunately, an 80-meter fragment continues to hurtle toward Earth.
Early estimates suggest that it could end up on the east coast of the
United States or in the Atlantic Ocean.
Manhattan will be a field of ruins
The Americans then prepared for a final mission with a nuclear charge
that would allow it to deflect.
Which had saved Tokyo during the previous "planetary defense"
exercise -- but political disagreements stopped the project...
Six months before the impact, specialists reveal that it is headed for
the New York area.
And two months before, it is certain: the bolide will destroy the city.
The asteroid will enter the atmosphere at 69,000 kilometers per hour and
explode about 15 kilometers above Central Park, scientists say.
The energy released will be 1,000 times that of Hiroshima. The blast
will destroy everything within a 10-mile radius -- the "no-survival"
zone.
Manhattan will be a field of ruins. Glass will explode up to 45
kilometers away. The damage will extend up to 68 kilometers.
