[meteorite-list] Asteroid Impact Evidence Found in Cuba

[Ron Baalke]

http://www.periodico26.cu/english_new/features/meteorite200605.htm

The Meteorite that Killed the Dinosaurs
By Ricardo Potts
Periodico 26 (Cuba)

The catastrophe that wiped out those reptiles and many other species 60
million years ago has been clarified.  The meteorite that caused their
deaths left its largest evidence in Cuba.

Today it seems to be definitely accepted, said Dr. Manuel Iturralde to
Sol y Son. Dr. Iturralde, a specialist with Cuba's National Museum of
Natural History, explained that the massive extinction 65 millions years
ago in which dinosaurs disappeared was caused by the meteorite of
Chixculub, Mexico.

The hypothesis of the "killer meteorite" emerged in 1979 when physicists
Harold Urey and Luis Alvarez found abnormal concentrations of iridium in
sediments from the late Cretaceous period Iridium is rare on Earth, but
there is plenty of it in asteroids and it is thought that the impact of
one with a diameter of over six miles induced earthquakes, volcanic
eruptions and a "nuclear winter" with a sudden drop in temperature.

Such an impact would make a crater with a 150 mile diameter.  Since none
like that was found on land, they looked for it at sea.  In 1990, Bohor
and Seitz, two US geophysicists, discovered that 650 thousand centuries
ago a giant meteorite fell in Chixculub, in the Yucatan peninsula,
Mexico, near the south-western coast of Cuba.

The evidence should be in the geological strata of the late Cretaceous
or early Tertiary periods, (K-T layer, according to experts), for its
lower part contains fossils of the disappeared animals, which were not
present in the upper part.  Also there should be quartz particles
crushed by the impact, as well as microtectites, or crystal balls formed
when the molten rock solidifies, usually found around meteor craters. 
And, of course, iridium.

Cuban Evidence

Iturralde's attention was caught by a paper published in Nature
magazine.  "I went to the Cuban areas where allegedly were fragments of
the impact", he explained, "but the rocks there were not originated by a
meteor.  Two years later I published a paper on the subject in Earth and
Planetary Science and Letters."

In 1996 Dr. Takafumi Matsui, from the University of Tokyo, visited Cuba
with a project on the Tertiary geological limit and signed a
collaboration agreement with the Museum of Natural History and the
Institute of Geology and Paleontology. During the past five years
several expeditions studied the K-T layer in the provinces of Pinar del
Røo, Havana, Matanzas and Villa Clara.

Unique cuts were found, for if the deposits in Mexico and other
countries of the area are 6 to 10 feet deep, in Cuba they go down to
almost three thousand.  "They are unique', Iturralde said, "and indicate
the most complete vestiges of the impact and its consequences."

What produced such unusual thickness?  When the meteorite fell in
Yucatan, what was then the bottom of the Caribbean and the edge of the
peninsula is now what is found in Pinar del Rio, Havana and Matanzas. 
That is, Cuba has rocks that were part of the bottom of the Caribbean
Sea and the Yucatan shores.

An Extraterrestrial Earthquake

According to Iturralde the impact generated a shock wave with an
earthquake way beyond any of terrestrial origin, so great that it
provoked an enormous crumbling of the continental edge in Yucatan, the
Bahamas platform and the then existing islands, which at present are the
foundation of Cuba. The crumbling made deposits hundreds of feet thick,
gaps with enormous blocks torn from the near emerging areas. "Gigantic
tsunamis crashed on the Caribbean coasts rolling over small islands and
low areas, with billions of tons of dust and sand. When they settled,
that material when to the bottom of the sea and created the huge layers
that we have found," said Iturralde The impact pulverized the meteorite,
rocks were fused and flew to the atmosphere, which received that
iridium-rich dust, crystals generated by the fusion and cooling of the
rock, and also laminar quartz. Due to the impact, all that is on Cuban rocks

Prehistoric Nuclear Winter

"Most probably all sea organisms in the Caribbean did not survive", said
Iturralde. "Not only dinosaurs were extinguished." At the International
Congress of Geology held in Havana, Dr. Ryuji Tada, a researcher from
the University of Tokyo, said that science links the impact with a world
environment crisis - acid rains, fragments falling from the sky and
cooling for a long period, because the particles in the atmosphere
blocked solar radiation, a kind of "prehistoric nuclear winter."

This brought massive deaths that in turn generated plagues, bacteria,
fungi and diseases for wildlife and flora, which in turn contributed to
the death of more species. The destruction of plants and forests left
them without food, the massive fallout and acid rains generated chemical
changes in the composition of the water in the seas, rivers and lakes.

Many species survived, but also many were totally extinguished, like
dinosaurs. At present there is a second project with universities from
Spain and Mexico, led by Reinaldo Rojas, the Museum's director, which
will study marine life before and after the impact, something that was
not done during the previous research.

"People sometimes wonder", concluded Iturralde, "why so much money is
spent on studying the past when there are so many problems today, but
those studies allow us to better know the whys of the present and
prepares us for the future. What happened in the past on Earth could
happen again, and all that history is in the rocks, so if we study them
we'll know what happened, what could happen and how to find ways to be
prepared for tomorrow."