A shark in the Thuringian Forest

Another piece of the puzzle has been found: Excavations in the Thuringian Forest bring new insights into the Earth’s history at the end of the Palaeozoic era.

Over the past two weeks, they have dug and dug hard, but the effort was worth it: researchers from the Freiberg Mining Academy uncovered a ten-metre-high rock wall on the outskirts of Oberhof in the Thuringian Forest. More than 100 fossils were found in it – including crabs, shells, ferns, but also traces of dinosaurs and freshwater sharks.

But what are sharks doing in the Thuringian Forest? The researchers can explain: Almost 300 million years ago, there was a large inland lake at this location. At that time, our continents were not yet separated by seas, but united in a supercontinent called Pangaea – and the Thuringian Forest was located between North America and Eastern Europe at that time.

For many millions of years, the remains of the inhabitants were deposited at the bottom of the inland lake. But about 250 million years ago the climate changed: it became drier and hotter and the lake dried up. Today, only the fossils bear witness to this time.

The largest dinosaur graveyard in the world

The heart of every palaeontologist beats faster here: the city of Zhucheng in the eastern Chinese province of Shandong is considered the “dinosaur capital” worldwide. Since the 1960s, dinosaur bones have been found in the area again and again. To date, more than 50 tons have been found, including a spectacular discovery of thousands of fossils in 2008. Now the excavations find their place in the recently opened Tyrannosaurus Museum.

Saurian sensation: baby dinosaur discovered in Bavaria

The fossil of a baby dinosaur was discovered in a lime works in Kelheim, Bavaria. The small predatory dinosaur is 98 per cent preserved. This makes it the best-preserved dinosaur fossil in all of Europe.

The baby dinosaur, which lived millions of years ago and fed on dragonflies, lizards and beetles, measures 72 centimetres. With its long tail, the little predatory dinosaur kept itself balanced. That was not easy with the weight of its large skull. This dinosaur probably did not live more than a year. On the other hand, it survived the next 135 million years in the earth quite well: Remains of skin, hair and even feathers are still clearly visible on the fossil. However, it could not fly. It lacked flight feathers and the corresponding musculature.

For science, the find is a real sensation. The small predatory dinosaur is the most important fossil from Germany since the discovery of the archaeopteryx bird.

Finding fossils on the Altmühl River

In prehistoric times, the area of today’s Altmühl was on the edge of a tropical sea. The climate was much warmer, fish dinosaurs, crabs, crocodiles and the prehistoric bird “Archaeopteryx” frolicked in and around the shallow waters. Today, the remains of these animals can be found in the form of fossils. One of them is the recently discovered baby dinosaur from Kelheim. A few kilometres upstream, in the Solnhofen plate limestone, the world-famous specimens of the prehistoric bird Archaeopteryx were discovered. Meanwhile, anyone can go hunting for fossils there: The Solnhofen Museum offers guided tours of the quarry, where visitors can split limestone slabs and search for fossils.

The Earth Ages

Since its formation, the earth has changed a lot: Mountains, oceans and continents have formed and passed away, animal and plant species have spread and become extinct. Most of these changes happened very slowly, over many millions of years. But every now and then there were drastic events: Within a few thousand years, environmental conditions changed drastically.

For the scientists who study the history of the Earth, these drastic changes are like a new chapter in a book: they divide the Earth’s history into different sections called eons.

At the beginning, 4.5 billion years ago, the Earth was completely uninhabitable. It emerged as a hot ball of glowing molten rock surrounded by hot, corrosive and toxic gases. This sounds like a description of hell – and from the Greek word “Hades” for hell also comes the name of this time: Hadaic. It ended about four billion years ago with the first major change: the earth had cooled down so much that the surface became solid – the earth got a crust.

The earth cooled further so that liquid water could collect on the crust: Oceans were formed. And in these seas, life began about 3.8 billion years ago – but initially only in the form of the simplest bacteria. The Greek word for origin or beginning is in the name of this period: Archaic. An important climatic change about 2.5 billion years ago marked the transition to the next epoch: primitive organisms began to influence the environment. They produced oxygen, which until then had been almost non-existent in the atmosphere.

The early unicellular life forms became more complex over time, forming cell nuclei. Later, some also began to work together permanently in associations – this eventually became the first multicellular organisms. However, they did not yet have solid shells or skeletons, so that hardly any fossils have survived from this period. The epoch owes its name to this period before the emergence of fossils: Proterozoic.

The Proterozoic ended 550 million years ago with an explosion of life: within a short time, an enormous variety of species developed from the primitive forms of life. These species were much more complexly built – and some also already had hard shells, which were preserved as fossils for the first time. Therefore, for scientists, the history of life only really becomes visible from this point onwards. And this epoch is also named after the Greek term for “visible”: Phanerozoic.

This age of life has lasted for 550 million years until today. However, the development of life did not proceed evenly: After the explosive spread of life, there were two devastating mass extinctions. These mark further important cuts in the Earth’s history, so that scientists divide the age of life, the Phanerozoic, into three sections called eras.

The oldest era of the Phanerozoic began 550 million years ago with the mass emergence of new species. It is called the Palaeozoic Era. At first, life took place only in the oceans. Then plants colonised the land, and later the animal world followed suit: First, amphibians developed, which were already able to venture a little on land, and finally also reptiles, which became independent of the water and conquered the land. The Palaeozoic ended about 251 million years ago with the greatest mass extinction of all time: More than 90 percent of all animal and plant species became extinct, especially in the oceans. The reason for this has not yet been conclusively explained. Scientists suspect that an ice age was to blame, possibly as a result of a meteorite impact.

When the surviving animal and plant species had to get used to their new environment, the Mesozoic era began. It is above all the age of the dinosaurs: giant lizards evolved and dominated life for almost 200 million years. But the Mesozoic also ended with a drastic event: about 65 million years ago, a large meteorite struck the Earth. It threw so much dust and ash into the air that the sky darkened and the climate changed for a long time. The dinosaurs and many other species became extinct.

Small mammals in particular, which were best able to adapt to climate change, benefited from this. They had already evolved in the Earth’s Middle Ages, but had remained in the shadow of the dinosaurs. Now they were able to spread rapidly, conquer a wide variety of habitats and continue to evolve. Humans are also descended from this group. This most recent age continues to this day and is therefore also called the Earth’s New Era or Cenozoic Era.

This rough classification of Earth history is oriented towards very drastic changes in life: explosive proliferation or mass extinction. In between, however, there were further upheavals due to various other influences – changes in the oceans and continents due to continental drift, climate change between ice ages and warm periods, composition of the air and much more. Invariably, the new conditions favoured some species and disadvantaged others. Thus, the three sections of the Phanerozoic (Age of Life) can still each be divided into several periods.

The supercontinent Pangaea

If you look at a world map a little more closely, you will notice: the shapes of Africa fit North and South America almost as well as pieces of a jigsaw puzzle. And indeed, the continents are something like puzzle pieces pushed apart. Only when put together, they do not form a picture, but a single large continent: Pangaea.

Pangaea existed about 250 million years ago. In this supercontinent, all land masses of the earth were combined and surrounded by a single sea, called Panthalassa. About 200 million years ago, Pangaea broke into two parts – Laurasia in the north and Gondwana in the south. The two continents later broke into even smaller pieces. After that, North and South America, Africa, Asia and Europe were already roughly recognisable in their present form. However, at that time these continents were much closer together than they are today. Only in the course of time did they become more and more distant from each other, because a mid-ocean ridge had broken up between America in the west and Africa and Eurasia in the east. A new ocean was formed: the Atlantic Ocean, which continues to grow today. North and South America therefore move away from Europe and Africa by a few centimetres every year.

Currents in the earth’s hot interior are the motor for the travel of the earth’s parts and the formation of oceans. These set the plates in motion very slowly. In some places, the plates move away or break apart as a result, while in other places they drift back towards each other.

But it is not only the shape of the continents that tells us how they were once connected. Mountain ranges also indicate where parts of the earth were one long ago. The Appalachian Mountains in the north-east of America, for example, are part of a mountain range that stretches across Greenland and Scotland to Norway. The mountains were separated by the North Atlantic Ocean, which has slid in between over the course of time. This mountain range, which was connected millions of years ago, can still be seen clearly on a map of the world.

From bone to stone: fossils

What we know about life in times long past is largely due to fossilised remains of living beings: fossils. Such fossils are formed when plants or animals are buried under layers of sediment after their death. The soft parts of the living beings decompose, while hard parts, such as teeth, bones or shells, remain. When mighty layers of rock weigh down on these remains, they are slowly pressed into rock under the growing pressure.

To discover a fossil, you don’t necessarily have to drill deep into the earth. When the rock layers rise over millions of years, deeper layers are also pushed upwards and exposed by erosion. In this way, fossils from the lowest layers of the seabed, as is the case in the limestone Alps, can reach high mountain peaks.

But not only in rock, also in the resin of trees plants and animals, such as mosquitoes or beetles, are caught. Over a long period of time, the sticky tree resin turns into solid amber. In this yellowish-transparent rock, insects or plants that lived millions of years ago can still be seen very clearly today.

How sweet is fresh water?

Although it does not taste sweet at all, it is called fresh water. Unlike salt water, it contains no or only very small amounts of salt and therefore has hardly any taste. For this reason, it is also well suited for obtaining drinking water.

Freshwater is rare: Of all the water on earth, only two to three percent is fresh water. Most of it is found in the high mountains and at the two poles. There it is stored as ice in glaciers. Only a very small fraction of the fresh water on earth flows in streams and rivers or splashes in lakes and groundwater. The water in clouds and precipitation is also “sweet”.

Why are there ice ages and warm periods? Natural climate changes

At the height of the last great ice age, it was bitterly cold. So cold, in fact, that a third of the land area disappeared under thick ice sheets. All that happened about 20,000 years ago. Over the millennia, temperatures rose again. Today we live in a warm period and only ten percent of the land surface is still iced over. But it was far from the first climate change on our planet. Since the earth was formed 4.6 billion years ago, it has sometimes been warmer and sometimes colder – without any human involvement. But why?

Climate researchers have been trying to find out what triggers natural climate changes for a long time. One explanation is that the earth “wobbles” a bit when it orbits the sun. This can be thought of as similar to a spinning top, but on a much larger scale. Both the tilt of the Earth’s axis and its orbit shift over thousands of years, in a regular cycle. This “egging” also changes the amount and distribution of the incoming solar energy. Over long periods of time, this causes temperatures to fluctuate, leading to ice ages and warm periods.

The distribution of the continents also plays a role in the fluctuations. Because their position has constantly shifted in the course of Earth’s history. When large land masses reached the North or South Pole, enormous amounts of ice could accumulate there. The ice reflected a large part of the sun’s rays and it became even colder. Only when the continent moved away from the pole again did the temperatures rise and an end to the ice age was in sight.

The composition of the atmosphere also affects the climate. The greater the proportion of greenhouse gases, such as carbon dioxide or water vapour, the more the atmosphere heats up. Its gas mixture can be changed by natural processes, for example by a volcanic eruption. When a volcano spews fire and ash, tiny particles are thrown high into the air, the aerosols. They reflect the sun’s rays before they reach the earth’s surface. The temperature on Earth drops – at least for a short time. Thus, the eruption of the Tambora volcano in 1815 was followed by a “year without summer”. At that time, snowstorms swept across the east coast of North America in the middle of the warmest season of the year. The result was catastrophic crop failure.

In contrast to these natural climate changes throughout history, the current climate change is caused by humans themselves. The fact that the average temperature has been rising for a good 150 years is mainly due to the fact that humans are producing more and more carbon dioxide