A Dramatic Chapter in the History of the Earth

Why did Stevns Klint earn a place on the UNESCO World Heritage List? Because it is the best place in the world to see Fish Clay and witness traces of the asteroid impact that helped wipe out more than half of all life on Earth.

World Heritage Site is the recognition and commitment given by UNESCO to Stevns Klint in 2014. UNESCO World Heritage Site means that the place has particular universal significance for all of humanity, and for present and future generations.

The cliff is a UNESCO World Heritage Site, because between the cliff’s thick layer of chalk and limestone there is a thin layer of Fish Clay, which tells the story of how the ecosystems of the Earth were pressured by the eruption of so-called ‘super volcanoes’, and of how an asteroid struck and put an end to the history of the dinosaurs. The Fish Clay is a greyish-brown layer of clay of just 5-10 centimetres, so it can be difficult to spot. Nor is the Fish Clay always above the surface of the sea. You cannot be sure of getting close to the Fish Clay, so we advise you to look through the telescopes at Højerup Old Church or from the beach below.

There are two vantage points in Højerup where telescopes are available. Right here by the Church and a little further south, just past the steps that lead down to the beach.

More than 66 million years ago, Stevns Klint did not exist. At that time, the whole of Denmark and large parts of Northern Europe were covered by the Cretaceous Sea.
The dinosaurs lived on land, while sharks, giant mosasauri, fish, ammonites, sea urchins and tiny algae lived in the sea.

For many years, scientists were confident that the great mass extinction at the end of the Cretaceous was the result of volcanic activity in what is present-day India. The theory was that the volcanic activity gradually acidified living conditions on Earth, and polluted the atmosphere with dust and toxic gases. But the geologist, Walter Alvarez and his father, also a geologist, were sure that there had to be another reason: something, which in a single stroke darkened the sky. So they pursued their theory of a giant asteroid.

In 1978, Alvarez came to Denmark and took samples of the Fish Clay, because everyone agreed that the thin grey stripe illustrated the moment life on Earth underwent a violent change. The samples showed large amounts of the element iridium. It is an element that does not occur naturally on Earth, but is found in large quantities in space. The find underpinned Alvarez’s theory, but no one could find a crater that was large enough to explain a mass extinction on that scale.

Walter Alvarez took samples of the Fish Clay in 1978. Today, touching the Fish Clay and cutting into the cliff are forbidden.

The theory divided geologists around the world. Some believed in the volcano theory, others in the asteroid theory. But in 1992, a giant crater was discovered on the Yucatán Peninsula in Mexico near the town of Chicxulub, after which the crater was named. The crater was created at the end of the geological period known as the Cretaceous, caused by an asteroid of 10 kilometres in diameter. The impact was so violent that it corresponded to 96 teratons of TNT. It then spewed out such huge amounts of ash into the atmosphere that the entire Earth was shrouded in a dark cloud that created a global nuclear winter.

More than 50% of the flora and fauna, which was already plagued, finally yielded – in the Cretaceous Sea too. Certain species of fish, sea urchins, algae and sharks survived, but they became smaller in size because of less food. On the surface of the earth, almost all predators had disappeared. But that was our good fortune, because now the mammals that had survived did not get eaten every time they appeared. The mammals adapted to the food, they reproduced rapidly, and thus coped in the pressurised ecosystems.

Today, we know that the dinosaurs were already extinct before the asteroid impact, so it was the convergence of super volcanoes and the asteroid impact that wiped out some of our planet’s most iconic creatures. So the mammals evolved in such a way that the mass extinction became the beginning of life as we know it today. The dust from the atmosphere descended and settled across the entire planet. It scattered onto the ocean floor, forming a new layer on top of the many metres of dead algae that formed the chalk bottom. Then came other creatures, whose skeletons turned into the layer of limestone at the very top of the cliff.

Illustrations: Sune Elskær og Tor Fruergaard.