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1. Denmark's History - Cretaceous

The Cretaceous period lasted from 145 million years to 65 million years before present. It was the last dinosaur period.

Timeline around Cretaceous The world in Cretaceous
Top: Timeline of Earth geological periods around the Cretaceous era, which began 140 million years before present. Earth's age is assumed to be 4.54 billion years (9 zeros), which is 4.54 billion years (6 zeros) - Cretaceous is a comparatively recent period in Earth's geological history.

Bottom: Throughout Cretaceous "Denmark" was covered by the shallow tropical Tethys Sea.

The dinosaurs have never set their feet on Danish soil, because the part of earth's crust, which later would become Denmark, was by then washed by a shallow tropical ocean called Tethys Sea.

The whole period of the dinosaurs is named the Mesozoic and is often called Earth Middle Ages. It includes the periods of Triassic, Jurassic and Cretaceous.

In Cretaceous the continents had almost reached their current positions, and the seas at the poles began shortly to freeze. At the beginning of the period there could be occurrence of snow at higher latitudes. But as the water had not yet been bound in today's large ice sheets, sea levels were still very high; it could be somewhere between 40 and 250 m. higher than today.

Deep underground Denmark is built on a foundation of chalk, which extends from the Baltic Sea east of Zealand and under the North Sea to England. but only in some places, such as on Møens Klint on Zealand and Dover in England, the white chalk comes to light.

Chalk in the underground Møens Klint
Left: A thick layer of chalk in underground is stretching from the Baltic Sea to the English Channel, but only on Møns Klint, Dover and a few other locations it comes to the surface.
Right: Møns Klint.

In the Tethys Sea lived myriads of microscopic algaes. They had a shell of chalk. When they died, the shells sank to the bottom, and through many millions of years, they deposited as a thick layer of chalk on the bottom of the ocean. Since all the shells were extremely small, the chalk is also very fine-grained - Easy to write with.

The chalk deposition first started in the mid-Cretaceous, but continued well into the following tertiary period.

Fossils from the 
cretaceous period
Fossils from the cretaceous period - left a belemnites, which was a now extict relative to squids.
Right a petrified sea urchin - Photo Henning Søder.

In this warm sea also lived a variety of octopus, sea urchins, clams, sharks, oysters, starfish and fish. The 15 m. long mosasaur killer lizard, a swimming dinosaur, lived there too.

In the mild climate of the cretaceous-era emerged flowering plants, and the first grass species sprouted. Among the animals on land dinosaurs were dominant.

Lif in the Tehtys Sea
In the Tehtys Sea lived squid, fish and sharks, and the 15 m long swimming killer dinosaur, Mosasaur.

It is assumed that the temperature of the Cretaceous were 6 to 12 degrees warmer than today (Antón Uriarte), with an annual average temperature of perhaps 15-20 degrees in the Arctic Ocean, which is much warmer than today. Maybe the average temperature in the area of northern Tehtys Sea, where Denmark was to be, was about 14-20 degrees, which is quite different from today's Danish annual average temperature of 8 degrees.

The high temperature of period was with some probability caused by a high CO2 content in the atmosphere and in particular a high content of water vapor. By counting the number of slits on the underside of fossil leaves has been concluded that the CO2 concentration in the Cretaceous atmosphere was 4-5, and sometimes up to 7 times as big as it is today.

All Earth's dinosaur species became extinct at the same time 65 million years ago. Many researchers believe that the cause of the giants extinsion was that Earth was hit by a very large comet or asteroid with a diameter of about 6-15 kilometers. A big crater on the Yucatan Peninsula in Central America can be dated to 65 million years ago, and it is believed be the place of impact.

The dinosaurs were 
wiped out by a large meteor
Many believe that the cause of the dinosaur's extinction was that Earth was hit by a huge meteor, producing a "nuclear winter".

The impact threw up huge amounts of dust that acting together with smoke from extensive fires and perhaps volcanic activity rose up in the atmosphere and troposphere. At 10 - 15 kilometers above the Earth's surface the particles were heated by the sun thus gaining the energy to float up into the stratosphere, where the they could not be washed out by rain. Here the particles remained for several years blocking the sun's rays thereby producing many years of "nuclear winter".

This dramatic and longlasting temperature drop wiped out the dinosaurs, one of the most successful species that ever existed on planet Earth. Many and varied species of dinosaurs emerged and disappeared over a period of 165 million years since the Triassic period 230 million years ago, on through the following Jurassic and Cretaceous periods, until their final exit approximately 65 million years ago..

Some scientists believe, however, that dinosaurs are not completely extinct. Birds can have evolved from dinosaurs. They support their theory by the facts that both dinosaurs and birds have three toes on the feet, they have air-filled bones, and they have the typical "wishbone" bone in common, additionally it has been demonstrated that some dinosaurs had feathers.

The Dinosaur's exit marked the end of the Cretaceous era.
Fortidens Drivhusverden: Geoviden - Geologi og Geografi Nr. 4 (pdf) Indsigt for fremtiden (Danish).
Earth's long-term sea-level history is characterized by widespread continental flooding in the Cretaceous period. However, published estimates of the Late Cretaceous sea-level high differ by half an order of magnitude, from ca. 40 to ca. 250 meters above the present level: Long-Term Sea-Level Fluctuations Driven by Ocean Basin Dynamics af R. Dietmar Müller, Maria Sdrolias, Carmen Gaina, Bernhard Steinberger og Christian Heine.
See henningsoder.com with good photos of fossils and Møns Klint.

Siberian Discovery Suggests Almost All Dinosaurs Were Feathered National Geographic.

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