The continent of Europe is a landmass bounded on the east by the Ural Mountains, on the south by the Mediterranean Sea, and on the north and west by the Arctic and Atlantic Oceans. Numerous islands around this landmass are considered a part of Europe. Europe is also the westernmost part of the Eurasian supercontinent (several continental masses joined together). Europe is a collection of different kinds of geologic regions located side by side. Europe holds a unique place among the continents; much of it is new, in geologic terms.
Plate tectonics is the main force of nature responsible for the geologic history of Europe. European geologic history, like that of all the continents, involves the formation of features as a result of plate tectonics.
When the edge of a plate of Earth's lithosphere runs over another plate, forcing the lower plate deep into the elastic interior, a long, curved chain of volcanic mountains usually erupts on the forward-moving edge of the upper plate. When this border between two plates forms in an ocean, the volcanic mountains constitute a string of islands (or archipelago). This is called an island arc. Italy's Appenine Mountains originally formed as an island arc, then later became connected into a single peninsula.
A continental arc is exactly like an island arc except that the volcanos erupt on a continent, instead of in the middle of an ocean. The chemical composition of the erupted rock is changed, because old continental rocks at the bottom of the lithosphere have melted and mixed with the magma. A clear-cut example of this kind of mountain chain no longer exists in Europe, but ancient continental arcs once played an important part in Europe's geologic past. Sicily's Mt. Aetna and Mt. Vesuvius on the Bay of Naples are good examples of the type of volcano that commonly make up a continental arc.
A suture describes the place where two parts of a surgery patient's tissue are sewed or rejoined; it also describes the belts of mountains that form when two continents are shoved into each other, over tens of millions of years, to become one. The Alps and other ranges in southern Europe stand tall because of a continental collision between Europe and Africa. The Alps, and other European ranges, are the forerunners of what may be a fully developed suture uniting Europe and Africa. This suture would be a tall mountain range that stretches continuously from Iberia to easternmost Europe.
The collision of Africa with Europe is a continuous process that stretches tens of millions of years into the past and into the future. All the generations of humanity together have seen only a tiny increment of the continental movement in this collision. However, throughout history, people have felt the collision profoundly, in earthquakes and volcanos, with all the calamities that attend them.
Sometimes a continent is torn in pieces by forces moving in opposite directions beneath it. On the surface, this tearing at first makes a deep valley, which experiences both volcanic and earthquake activity. Eventually the valley becomes wide and deep enough that its floor drops below sea level, and ocean water moves in. This process, called rifting, is the way ocean basins are born on Earth; the valley that makes a place for the ocean is called a rift valley. Pieces of lithosphere, rifted away from Africa and elsewhere, have journeyed across the Earth's surface and joined with the edge of Europe. These pieces of lithosphere lie under southern England, Germany, France, and Greece, among other places.
When a continent-sized "layer cake" of rock is pushed, the upper layers move more readily than the lower layers. The upper layers of rock are heavy but easier to move than those beneath it (much like a full filing cabinet is heavy but, when pushed, moves more easily than the floor beneath it). Between near surface rocks and the deeper, more ancient crustal rocks, a flat-lying fault forms, also called a detachment fault. This horizontal crack, called a thrust fault, contains fluid (water, mostly). The same hydraulic force that makes hydraulic machines lift huge weights functions in this crack as well. The fluid is so nearly incompressible that a sizeable piece of a continent can slide on it when pushed. The fault block floats on fluid pressure between the upper and lower sections of the lithosphere like a fully loaded tractor trailer gliding effortlessly along a rain-slicked road. The mountains that are heaved up where the thrust fault reaches the surface are one kind of fault block mountains. Both the Jura Mountains and the Carpathians are fault block mountains.
Europe was not formed in one piece, or at one time. Various parts of it were formed all over the ancient world, over a period of four billion years, and were slowly brought together and assembled into one continent by the processes of plate tectonics. What is now called Europe began to form more than 3 billion years ago, during the Archean Eon.
Most geologists feel that prior to and during the creation of the oldest parts of Europe, Earth only superficially resembled the planet we live on today. Active volcanos and rifts abounded. The planet had cooled enough to have a solid crust and oceans of liquid water. The crust may have included hundreds of small tectonic plates, moving perhaps ten times faster than plates move today. These small plates, carrying what are now the earth's most ancient crustal rocks, moved across the surface of a frantic crazy-quilt planet. Whatever it truly was like, the oldest regions in Europe were formed in this remote world. These regions are in Finland, Norway (Lofoten Islands), Scotland, Russia, and Bulgaria.
The piece of Europe that has been in its present form for the longest time is the lithospheric crust underneath Scandinavia, the Baltic states, and parts of Russia, Belarus, and Ukraine. This region moved around independently for a long time, and is referred to as Baltica. It is the continental core, or craton, to which other parts were attached to form Europe.
At the opening of the Mesozoic Era, 245 million years ago, a sizeable part of western and southern Europe was squeezed up into the Central Pangean mountain system that sutured Laurasia and Gondwana together. Pangea was the huge landmass from which all continents drifted; Laurasia and Gondwana were the two supercontinents that Pangea separated into about 200 million years ago. Europe was almost completely landlocked, its southern regions part of a mountain chain that stretched from Kazakhstan to the west coast of North America.
The birth of a new ocean basin, the Atlantic, signaled the end of Pangea. The Central Pangean Mountains, after tens of millions of years, had worn down to sea level and below. A new ocean basin, not the Mediterranean, but rather the Ligurean Ocean, began to open up between Africa and Europe. This formed a seaway between the modern North Atlantic and the Neo-Tethys Ocean (which no longer exists). Sea water began to leave deposits where high mountains had stood, and a layer cake of sedimentaid down on the shallow sea bottomegan to accumulate throughout Europe.
Beginning at the close of the Mesozoic Era (66 million years ago), and continuing through the Cenozoic Era to the present day, a complex orogeny (mountain building) has taken place in Europe. The ocean basin of Tethys was entirely destroyed, or if remnants still exist, they are indistinguishable from the ocean crust of the Mediterranean Sea. Africa has shifted from west of Europe (and up against the United States' East Coast) to directly south of Europe, and their respective tectonic plates are now colliding.
As in the collision that made the Variscan mountain belt, a couple of dozen little blocks are being pushed side-ways into southern Europe. The tectonic arrangement can be compared with a traffic jam in Rome or Paris, where numerous moving objects attempt to wedge into a space in which they cannot all fit.
When sea level fell below the level of the Straits of Gibraltar around six million years ago, the western seawater passage from the Atlantic Ocean to the Mediterranean Sea closed, and water ceased to flow through this passage. At about the same time, northward-moving Arabia closed the eastern ocean passage out of the Mediterranean Sea and the completely landlocked ocean basin began to dry up. Not once, but perhaps as many as 30 times, all the water in the ancestral Mediterranean, Black, and Caspian Seas completely evaporated, leaving a thick crust of crystallized sea minerals such as gypsum, sylvite, and halite (salt). It must have been a lifeless place, filled with dense, hot air like modern below-sea-level deserts such as Death Valley and the coast of the Dead Sea. The rivers of Europe, Asia, and Africa carved deep valleys in their respective continental slopes as they dropped down to disappear into the burning salt wasteland.
Many times, too, the entire basin flooded with water. A rise in global sea level would lift water from the Atlantic Ocean over the barrier mountains at Gibraltar. Then the waters of the Atlantic Ocean would cascade 2.4 mi (4 km) down the mountainside into the western Mediterranean basin. From Gibraltar to central Asia, the bone-dry basin filled catastrophically in a geological instant few hundred years. This "instant ocean" laid deep-sea sediment directly on top of the layers of salt. The widespread extent and repetition of this series of salt and deep-sea sediment layers is the basis for the theory of numerous catastrophic floods in the Mediterranean basin.
For reasons not yet fully understood, Earth periodically experiences episodes of planet-wide climatic cooling, the most recent of which is known as the Pleistocene Epoch. Large areas of the land and seas become covered with ice sheets thousands of feet thick that remain unmelted for thousands or hundreds of thousands of years. Since the end of the last ice age about 8,0002,000 years ago, only Greenland and Antarctica remain covered with continent-sized glaciers. But during the last two million years, Europe's northern regions and its mountain ranges were ground and polished by masses of water frozen into miles-thick continental glaciers.
Ice in glaciers is not frozen in the sense of being motionless. It is in constant motionmperceptibly slow, but irresistible. Glaciers subject the earth materials beneath them to the most intense kind of scraping and scouring. An alpine glacier has the power to tear bedrock apart and move the shattered pieces miles away. These are the forces that shaped the sharp mountain peaks and u-shaped mountain valleys of modern Europe. Many European mountain ranges bear obvious scars from alpine glaciation, and the flat areas of the continent show the features of a formerly glaciated plain.
Humans have lived in Europe for much of the Pleistocene Epoch and the entire Holocene Epoch (beginning at the end of the last ice age, about 10,000 years ago). During the past few thousand years, humans have been significantly altering the European landscape. Wetlands across Europe have been drained for agricultural use from the Bronze Age onward. The Netherlands is famous for its polders, below-sea-level lands made by holding back the sea with dikes. Entire volcanoes (cinder cones) have been excavated to produce frost-resistant road fill.
The northwest fringe of Europe is made up of the two very old islands, Great Britain and Ireland, and numerous smaller islands associated with them. Geologically, these islands are a part of the European continent, although culturally separate from it. Unlike many islands of comparable size, the British Isles do not result from a single group of related tectonic events. They are as complex as continents themselves, which in the last two centuries has provided plenty of subject matter for the new science of geology.
Scotland and Ireland are each made of three or four slices of continental crust. These slices came together around 400 million years ago like a deck of cards being put back together after shuffling.
The Iberian Peninsula, occupied today by Portugal and Spain, is one of the pieces of lithosphere that was welded to Europe during the Variscan mountain-building event. Like Britain, it is an unusual "micro-continent" with a complex geologic history.
Since the Paleozoic Era, southern Europe has continued to acquire a jumbled mass of continental fragments from Africa. Even today, the rocks of Europe from the Carpathian Mountains southwestward to the Adriatic and Italy are made up of "tectonic driftwood," and are not resting on the type of solid, crystalline basement that underlies Scandinavia and Ukraine.
Since the late Mesozoic Era, the widening Atlantic Ocean has been pushing Africa counterclockwise. All the blocks of lithosphere between Africa and Europe, including parts of the Mediterranean seafloor, will in all likelihood eventually become a part of Europe.
The Alps resulted from Europe's southern border being pushed by the northern edge of Africa. In Central Europe, freshly-made sedimentary rocks of early Mesozoic age, along with the older, metamorphosed, Variscan rocks below, were pushed into the continent until they had no other way to go but up. Following the path of least resistance, these rocks were shaped by powerful forces into complex folds called nappes, which means tablecloth in French. The highly deformed rocks in these mountains were later carved into jagged peaks by glaciers during the Pleistocene Epoch.
The Jura Mountains, the Carpathians, and the Transylvanian Alps are made of stacks of flat-lying sedimentary rock layers. These mountain ranges were thrust forward in giant sheets out in front of the rising Alps.
A complex story of tectonic movement is recorded in the sea-floor rocks of the western Mediterranean. Corsica, Sardinia, Iberia, and two pieces of Africa called the "Kabylies"ormerly parts of Europeoved in various directions at various speeds throughout the Cenozoic Era.
On the western Mediterranean floor, new oceanic lithosphere was created. Asubduction zone formed as an oceanic plate to the east sank below the western Mediterranean floor. The magma generated by this event gave rise to the Appenine Mountains, which formed as an island arc on the eastern edge of the western Mediterranean oceanic plate. The Appenines began to rotate counterclockwise into their present position. The Tyrrhenian Sea formed as the crust stretched behind this forward-moving island arc. In the Balkans, blocks of lithosphere have piled into each other over tens of millions of years.
The Dinarides and Hellenides, mountains that run down the east coast of the Adriatic Sea, form the scar left after an old ocean basin closed. The compressed and deformed rocks in these mountain ranges contain pieces of ocean floor. Just east of these seacoast mountains is a clearly-recognized plate boundary, where the European and African plates meet. The boundary runs from the Pannonian Basin (in Hungary, Romania, and Yugoslavia), cuts the territory of the former Yugoslavia in half, and winds up in Greece's Attica, near Athens.
Further inland, the Pannonian Basin results from the lithosphere being stretched as the Carpathian Mountains move eastward and northward.
The Aegean Sea seems to have formed as continental crust has been stretched in an east-west direction. It is a submerged basin-and-range province, such as in the western United States. The Pelagonian Massif, a body of igneous and metamorphic rock that lies under Attica, Euboea, and Mount Olympus, forms part of the Aegean sea floor. The Rhodopian Massif, in northern Greece, Bulgaria, and Macedonia, also extends beneath the Aegean Sea. Faults divide the ridges from the troughs that lie between them. The faults indicate that the troughs have dropped into the crust between the high ridges.
The Balkan Range in Bulgaria is thought to mark the crumpled edge of the European cratonhe Proterozoic-age rocks extending north into Russia.
Europe is also host to isolated volcanoes related to structural troughs within the continent. The Rhine River flows in a trough known as the Rhine Graben. Geologists believe the Rhine once flowed southward to join the Rhone River in France, but was diverted by upwarping of the crust around the Vogelsberg Volcano. The Rhine then changed its course, flowing out to meet England's Thames River in the low-sea-level Ice Age.
Europe continues to change today. From the Atlantic coast of Iberia to the Caucasus, Europe's southern border is geologically active, and will remain so effectively forever, from a human frame of reference. Africa, Arabia, and the Iranian Plateau all continue to move northward, which will insure continued mountain-building in southern Europe.
Geologists are concerned about volcanic hazards, particularly under the Bay of Naples and in the Caucasus. In historic times, in the Aegean Sea and at Pompeii, Herculaneum, and Lisbon, entire cities have been devastated or destroyed by volcanoes, earthquakes, and seismic sea waves. These larger-scale natural disasters can and will continue to happen in Europe on an unpredictable schedule with predictable results.
See also Continental drift theory; Earth (planet); Historical geology
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