What are some hard stones

From bone to stone: fossils

What we know about the life of long past times, we owe to a large extent to the fossilized remains of living things: the fossils. Such fossils arise when plants or animals are buried under layers of sediment after their death. The soft parts of living beings decompose, hard parts such as teeth, bones or shells are preserved. When thick layers of rock weigh down on these remnants, they are slowly pressed into rock under the increasing pressure.

The younger fossils are usually found in the upper rock layer. The deeper you go into the sedimentary layers, the older the fossils that are stored there. Very old, but still frequently found fossils are, for example, the ammonites. These are the remains of shellfish that lived hundreds of millions of years ago and became extinct about 65 million years ago. Because they only lived for a limited period of time, it is possible to roughly determine the age of the rock in which they were found.

In order to discover a fossil, it is not necessary to drill deep into the earth. When the rock layers rise over the course of millions of years, deeper layers are also pushed upwards and exposed by erosion. In this way, fossils from the lowest layers of the sea floor, as is the case in the limestone Alps, can reach high mountain peaks.

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


The fossil of a baby dinosaur was discovered in a lime works in Kelheim, Bavaria. 98 percent of the small predatory dinosaur has been 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 centimeters. The little predatory dinosaur kept itself in balance with its long tail. That wasn't easy with the weight of his large skull. This dinosaur was probably not older than a year. On the other hand, it survived the next 135 million years that it lay in the earth: Remnants of skin, hair and even feathers can still be seen on the fossil. He couldn't fly, however. For this he lacked flight feathers and the corresponding muscles.

The find is a real sensation for science. For them, the small predatory dinosaur is the most important fossil from Germany since the ancient bird Archeopteryx was discovered.

Find fossils on the Altmühl river

Ancient times, the area of ​​today's Altmühl was on the edge of a tropical sea. The climate was significantly warmer, ichthyosaurs, crabs, crocodiles and the ancient bird "Archeopteryx" cavorted in and around the shallow water. 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 kilometers upstream, in the Solnhofen limestone, the world-famous specimens of the ancient bird Archeopteryx were discovered. Everyone can now go on a hunt for fossils there: the Museum Solnhofen offers guided tours of the quarry, where visitors can split limestone slabs and look for fossils.


Another piece of the puzzle has been found: excavations in the Thuringian Forest bring new insights into the history of the earth at the end of the ancient world.

In the past two weeks they have dug and dug properly, but the effort has paid off: Researchers from the Freiberg Mining Academy uncovered a ten-meter-high rock wall on the outskirts of Oberhof in the Thuringian Forest. Over 100 fossils were found in it - including crabs, mussels and ferns, but also traces of dinosaurs and freshwater sharks.

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

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

The largest dinosaur cemetery in the world

The heart of every paleontologist beats faster here: The city of Zhucheng in the east Chinese province of Shandong is known worldwide as the "dinosaur capital". Dino bones have been found in the area again and again since the 1960s. To date there are more than 50 tons, including a spectacular find of thousands of fossils in 2008. Now the excavations find their place in the recently opened Tyrannosaurus Museum.


Drei Zinnen, Rosengarten and Geislerspitzen - the steep rock groups of the Dolomites rise mightily over the otherwise gently undulating landscape. Because of their “unique monumental beauty”, the Dolomites have now been added to the UNESCO World Heritage List.

Its peaks protrude into the sky like sharp teeth. Anyone visiting the Dolomites is walking across ancient coral reefs and scrambling across the history of the earth. Like the entire Alps, the Dolomites began to rise and unfold from the sea floor millions of years ago. Over time, wind and weather formed gentle slopes at the foot of their peaks. Today cows graze here in summer.

Thousands of tourists come every year to marvel at the fabulous landscape. Extreme climbers perform circus-ready tricks on the steep walls. The fairytale-like setting attracts not only hikers and mountaineers, but also celebrities: Hollywood stars like George Clooney and Tom Cruise have already stayed here. And Reinhold Messner, himself born in Bressanone, began his career as an extreme climber on the walls of the Dolomites.

The World Heritage Committee was also impressed by the grandiose nature: On June 26th, parts of the Dolomites were declared a World Heritage Site by UNESCO. This means that the Dolomites are now under special protection.

How the “pale mountains” became the Dolomites

The Dolomites are also called “pale mountains” because of their color. The Ladins, the oldest inhabitants of the area, tell each other many stories about their mysterious mountains: There is talk of the dwarf king Laurin and his enchanted rose garden and of a dwarf people who have woven the peaks with threads of moonlight. This mountainous landscape has always stimulated the imagination.

The French geologist Déodat de Dolomieu, on the other hand, took a more sober look at her light rock. Upon closer inspection, he found that they were not made of pure limestone, as suspected. The salt magnesium oxide also had a large share. The newly discovered rock of the mountain range was named after its discoverer, Dolomieu: the dolomite. And the “pale mountains” turned - simsalabim - into the Dolomites.

Sedimentary rocks

Some rocks look like they're striped. In the Dolomites, for example, such transverse bands can often be clearly seen. Sandstone or limestone quarries sometimes have similarly pretty patterns.

The "stripe design" is created when the rock is formed. The starting material is weathered debris that is carried away by water or the wind. Rivers, glaciers and dust storms lose their strength at some point: the courses of rivers become slower and slower towards the mouth and finally flow into the sea or a lake. Glaciers are advancing into warmer regions and melting. Dust storms also subside at some point. Then they can no longer move dust, sand and rubble. The crushed rock that is dragged along settles out. Over time, the deposited material forms an ever higher layer - the sediment. Such sediments, including the remains of dead animals or limestone shells, collect particularly on the seabed and on the bottom of lakes, where rivers wash up a lot of material.

Gradually, different sediments are layered on top of each other. A layer can, for example, consist of sandstone: During the dry season, the wind blew desert sand here. If the sea level rises again, this layer is covered by water: the limestone shells of marine animals sink to the sea floor and deposit another layer over the sand. Over millions of years the climate changed again and again and made the sea level fluctuate. This allowed different layers to deposit.

Over time, the sediment cover becomes thicker and thicker. Under the weight of one's own weight, the initially loose sediments are compressed more and more, small cavities disappear, the mass condenses. Further layers are deposited over it, the sediment becomes more and more solid and finally becomes sedimentary rock under pressure. This process is also called diagenesis in geology. For example, if the shells of tiny marine animals are pressed into stone, limestone is created. Fine grains of sand made of quartz cement together under the high pressure to form sandstone.

In addition to rubble, dead animals also settled, for example fish on the ocean floor. Their bones and scales remained hermetically sealed and petrified. Such fossils are immortalized in the stone. Even after millions of years, they reveal a lot about the time in which the sediment was formed. Therefore, geologists can read in the rock layers like a history book.

Usually only the top layer is visible to us. However, when a river digs its way through the sedimentary rock, lifts it up during mountain formation, or blasts it free in a quarry, we get a glimpse of the cross-section. The individual layers of sediment can then be easily recognized as "stripes" or bands in the rock.

Cycle of rocks

No rock on earth is made to last. It weathers on the surface, is removed and redeposited. When two plates collide, layers of sediment are compressed and unfolded to form high mountains. The rock of submerged plates melts in the earth's interior and forms the source of volcanoes. Lava that spits out from a volcanic crater cools down and solidifies again into rock.

It is an eternal cycle that ensures that even the hardest rock is constantly changing and new things are created from it. The transformation does not happen overnight, of course, but over millions of years. "Players" in this cycle are three groups of rocks, each of which is formed under different conditions:

When magma cools, the hot mass solidifies igneous rock. This can happen both on the surface of the earth and inside the earth. On the other hand, where layers of excavated rock pile up, the sediments are compressed under the weight of their own weight. This pressure causes them to solidify Sedimentary rock. In turn, high pressure and great heat in the earth's interior ensure that rock is transformed and another is created. Then geologists speak of transformation or of metamorphic rock.

These three types of rock are closely related: each type can transform into any other. This rock cycle will continue as long as the earth exists.

What is rock?

In some places it peeps out from under a thin cover of plants, in other places it rises up as a steep rock face: the bare rock. It is the building material that makes up the earth's crust and mantle. However, rock is not a uniform mass. Similar to cake batter - only much harder - it is a mixture of different ingredients: the minerals.

Rock therefore consists of different minerals. Depending on their composition, the minerals combine to form certain types of rock. Granite, for example, is a rock made up of the minerals feldspar, quartz and mica. The fact that granite is made up of different minerals can already be seen from the fact that it is speckled: it contains lighter and darker parts, which owe their different color to three different minerals. The darker parts come from the mineral mica. The quartz mineral often appears whitish to gray. The third mineral, feldspar, can take on any color, even pink. Unlike the hard granite rock, the softer sandstone consists almost entirely of quartz. Because of this, sandstone looks more uniform than the speckled granite.

Almost all minerals are arranged according to a certain lattice pattern to form uniform shapes, the crystals. The mineral rock salt, for example, grows into a cube. The regular arrangement also results in other shapes with smooth surfaces, as can be seen well in a rock crystal. This consists of particularly pure and therefore transparent quartz. If, on the other hand, liquid is enclosed in the quartz, it turns milky in color. Then geologists speak of a milk quartz.

From rock to grain of sand - weathering

Today the north of Canada is a gently undulating landscape. However, many millions of years ago there was a mountain range here. In fact, even high mountains can turn into small hills over a very long period of time.

The reason for this transformation: The rock on the earth's surface is constantly exposed to wind and weather. For example, if water penetrates into cracks in the stone and freezes, it splits the stone apart. This process is called frost blasting. The rock also becomes brittle through temperature changes between day and night and through the power of water and wind. In other words: it weathers. This process can also be observed on buildings or on stone figures. During the weathering, the rock breaks down into smaller and smaller components up to fine grains of sand and dust. Different rocks weather at different rates: Granite, for example, is much more resistant than the comparatively loose sandstone.

Some types of rock even completely dissolve when they come into contact with water, for example rock salt and lime. Rock salt is chemically the same as table salt - and that already dissolves in ordinary water. Lime is a little more stable, but limestone also dissolves in acidic water. Acid is formed, for example, when rainwater in the air reacts with the gas carbon dioxide. This “acid rain” attacks the limestone and dissolves it over time. The weathering leaves rugged limestone landscapes on the surface of the earth, and caves are formed below the surface.

But not only solution weathering, heat and pressure also wear down and crumble rock under the earth's surface. Wherever plants grow, roots dig in, break up the rock piece by piece and also ensure that it is removed millimeter by millimeter.

In this way, weathering not only works on individual rocks, it gnaws at entire mountain ranges. It will take a few million years for the Black Forest to be as flat as northern Canada.

The geological ages

The earth has changed a lot since its formation: mountains, seas and continents have arisen and passed, 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 decisive events: within a few thousand years the environmental conditions changed drastically.

For the scientists studying 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, the Eons to be named.

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, caustic and poisonous gases. That sounds like a description of hell - and the name of this time comes from the Greek word "Hades" for hell: Hadaikum. It ended about four billion years ago with the first big change: The earth had cooled down so much that the surface became solid - the earth got a crust.

The earth continued to cool, so that liquid water could collect on the crust: seas were formed. And life began in these seas around 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 time: Archean. An important climate change about 2.5 billion years ago marked the transition to the next epoch: primitive living things began to influence the environment. They produced oxygen that was previously almost completely absent from the atmosphere.

The early unicellular life forms became more complex over time, they formed cell nuclei. Later, some began to work together on a permanent basis in alliances - this ultimately resulted in the first multicellular organisms. However, they did not yet have solid shells or skeletons, so that hardly any fossils have survived from this period. This epoch owes its name to this time before the fossils were formed: Proterozoic.

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

This age of life has lasted for 550 million years until today. However, life did not develop evenly either: After the explosive spread of life, there were two devastating mass extinctions. These mark further important turning points in the history of the earth, so that scientists divide the age of life, the Phanerozoic, into three sections, Eras called, divide.

The oldest era of the Phanerozoic began 550 million years ago with the mass emergence of new species. They are called that Antiquity or Paleozoic. At first life only took place in the oceans. Then the plants colonized the land, later the animal world followed suit: first the amphibians developed, which could already feel their way a little on land, and finally also reptiles, which became independent of the water and conquered the land. The ancient world ended about 251 million years ago with the greatest mass extinction of all time: Over 90 percent of all animal and plant species died out, especially in the oceans. The reason has not yet been finally clarified. 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, it broke Earth Middle Ages or Mesozoic at. It is primarily the age of the dinosaurs: giant lizards evolved and ruled life for almost 200 million years. But the Middle Ages also ended with a decisive event: about 65 million years ago a large meteorite hit the earth. So much dust and ash was thrown 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 benefited from this, as they were best able to adapt to climate change. They had already developed in the Mesozoic, but remained in the shadow of the dinosaurs. Now they were able to spread rapidly, conquer the most varied of habitats and keep developing. Humans also descend from this group. This most recent age continues to this day and therefore becomes the Earth New Age or Cenozoic called.

This rough division of the earth's history is based on very drastic changes in life: explosive multiplication or mass extinction. In between, however, there were further upheavals due to various other influences - changes in the seas and continents due to continental drift, climate change between ice ages and warm periods, the composition of the air and much more. The new conditions always favored individual species and disadvantaged others. So the three sections of the Phanerozoic (Age of Life) can each be divided into several periods.