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Europe - Forces That Made Europe, The Mediterranean Desert - Miscellaneous regions and events

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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 holds a unique place among the continents; much of it is "new," in geologic terms. Unlike other continents whose structures seem simple in comparison, Europe is a collection of all different kinds of geologic regions located side by side, many of which have little or nothing to do with each other. This should be kept in mind when reading about the regions in this article, which are not areas of similar origins, but rather areas of dissimilar origin that happen to be part of the same continent.


Large-scale geologic elements of Europe

European geologic history, like that of all the continents, involves the formation of the following features as a result of plate tectonics:

Island arcs: 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 became connected into a single peninsula later.

Continental arcs: 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.

Sutures: 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.

Rifts: 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.

Fault-block mountains: 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 (like a full filing cabinet is heavy-but when it's pushed, it 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 (decollement in French). 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.

Another kind of fault block mountain comes from stretching of the earth's lithosphere. The lithosphere, like any other brittle material, develops cracks perpendicular to the direction of movement of the forces that are pulling it apart. In this case the force is lateral, so steep, nearly vertical faults form.

However they form, physical and chemical forces start wearing down mountain ranges while they are still rising. Europe has been criss-crossed by one immense range of mountains after another throughout its almost four-billion year history. Where did these mountains go?

If mountains are not continuously uplifted, they are worn down by erosion in a few million years. In Europe's geologic past, eroded particles from its mountains were carried by streams and dumped into the surrounding ocean or the continent's inland seas. Those particular rivers and seas are now gone from Earth, but the sediments that filled them remain, like dirt in a bathtub when the water is drained. The roots of all the mountain ranges that ever stood in Europe still exist, and much of the sand and clay into which the mountains were transformed still exists also, as rock or soil formations.


European geologic history

Unfortunately, the farther back in a continent's history we attempt to explore, the less we can know about it. Only a very incomplete record of ancient geologic events is preserved for study because most ancient rocks are subsequently destroyed. For the most distant geologic time interval in Europe's history, from 4.6 billion years ago (b.y.a.) to 3.8 b.y.a., the Hadean eon, almost nothing is known and so it is not discussed here. Enough is known however about the Archean eon (3.8-2.5 b.y.a.), the Proterozoic eon (2.5 b.y.a.-570 million y.a.), and the Phanerozoic eon (570 m.y.a.-present) to provide a fairly detailed picture. In fact, the events of the Phanerozoic eon are known well enough to discuss them with even smaller geologic time intervals. These from largest to smallest are era, period, and epoch. The older the events, the less detail is known, so only very recent geologic epochs are discussed.


Archean rocks in Europe

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.


Proterozoic Europe

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 on its own 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.

In the two billion years of the Proterozoic eon (2.5 b.y.a to 570 m.y.a.), the geologic setting became more like the world as we know it. The cores of the modern continents were assembled, and the first collections of continents, or supercontinents, appeared. Life, however, was limited to bacteria and algae, and unbreatheable gases filled the atmosphere. Erosion clogged the rivers with mud and sand, because no land plants protected the earth's barren surface from the action of rain, wind, heat, and cold.

During the late Proterozoic an existing supercontinent began to break up. One of the better known episodes in this supercontinent's dismemberment was the Pan-African event. This was a period when new oceans opened up and mountains rose all around Africa. Over a period of a quarter-billion years, relatively small pieces of Africa tore away and were rafted along on the asthenosphere, colliding with Baltica. These blocks include: the London Platform (southern Britain); a strip of Ireland from between counties Wicklow and Kerry; the Iberian Peninsula (Spain and Portugal); Aquitaine, Armorica, and the Massif Central (France); the Inter-alpine region (Switzerland and Austria); the Austrian Alps (Carnic Alps); Bohemia; Moesia (Bulgaria and Romania); and the Rhodope region (Northern Greece, Bulgaria, and European Turkey, including Istanbul).

The result is that much of northern and central Europe, on a continental scale of reference, is made of blocks of Africa stuck together in a "paste" of sedimentary rock.

Most of the mountain belts created in the Proterozoic eon have long since worn away. The roots of these mountain belts are found in northern Europe and include:

The Karelian mountain belt, forming the middle third of Norway, Sweden, and Finland, including some of Karelia, is underlain by the worn-flat roots of the Karelian mountain range. This orogenic event (from oros, Greek for mountain, and genesis, Greek for origin) happened between 2 billion and 1.7 billion years ago.

The Svecofennian mountain belt, forming most of the southern third of Norway, Sweden, and Finland, are the roots of a Proterozoic mountain belt. They lie hidden beneath recent glacier-deposited sediments, and beneath dense coniferous forests. Because these factors make examination difficult, the Svecofennian mountain-building event is not yet well understood. It is presumed that the Svecofennian mountain belt marks where Baltica's edge was between 1.9 and 1.4 billion years ago. This mountain Europe. Illustration by Hans & Cassidy. Courtesy of Gale Group. belt rose in a time of worldwide mountain-building, and it may have been related to the assembly of North America's Canadian Shield.

The southernmost tips of Norway and Sweden were made in the SvecoNorwegian/Grenville orogenic event, between 1.2 and 0.9 billion years ago. This is the mountain chain that united Baltica with North America, before most of the western and southern parts of the European landmass existed.

The Ukrainian shield: At present, geologists do not agree on when or how the Ukrainian shield was put together. Parts of it were definitely in existence before the Proterozoic eon. During the Proterozoic it was assembled, and joined Baltica.

Paleozoic Europe

The sea washed over the oldest parts of Earth's surface many times during the three billion-plus years of Archean and Proterozoic history. Life flourished in the shallow tidewater for these 3,000 million years. Algae, one of the most ancient organisms, were joined later by worms and other soft-bodied animals. Little is known of early soft-bodied organisms, because they left no skeletons to become fossils. Only a handful of good fossilspreserved under very rare conditions-remain from the entire world's immense Precambrian, or combined Hadean, Archean and Proterozoic, rock records.

Then, about 570 million years ago, several unrelated lineages of shell-bearing sea animals appeared. This was the beginning of the Phanerozoic eon of earth history (from the Greek phaneros, meaning visible, and zoe, meaning life), which includes the time interval from 570 million years ago to the present day. The seas teemed with creatures whose bones and shells we have come to know in the fossil record. These include trilobites, brachiopods, the first fishes, and vast coral reefs. The first half of the Phanerozoic eon is called the Paleozoic era (from the Greek palaios, meaning ancient). For Europe, the Paleozoic era was largely a continuation of events that started in the late Proterozoic eon.

Remember, the map of the ancient Earth didn't look anything like a modern world map. As this new day of Earth's history began, Baltica sat near the south pole. Three oceans surrounded it, and each of these oceans shrank and closed during the Paleozoic. As plate tectonics shifted island arcs and already-formed blocks of crust around on Earth's surface, new rock came to be a part of the forming continent of Europe; underground masses of igneous rock accumulated near active margins of Baltica; and volcanos frequently erupted even as they do today in the Mediterranean region. Concurrent with this volcanic mountain-building, was the wearing-down of the volcanos, and the wearing-down of mountain cores, exposed by erosion. The sediment from the erosion of these igneous rocks accumulated at the borders of the continental blocks, and often became compressed into tightly folded rock masses only a few million years after they accumulated.

Baltica faced Greenland across the Iapetus Ocean. Early in the Paleozoic Era, Europe combined again with North America to form a giant continent called Laurussia (from Laurentia, meaning the core of North America, and Russia), or The North Continent. The line along which the continents were welded together runs along the length of Norway, through central Scotland, south-central Ireland, and southern Wales. In North America this line runs down the eastern coast of Greenland. As always happens when continents collide, there an associated mountain-building event. The resulting mountains are called the Caledonides, and they stood athwart the seam that welded Baltica and Laurentia together at that time. A continental arc developed, running from Denmark southeast down the ancient coast of Baltica, which is also considered to be a part of the Caledonian orogeny. Mountains in Norway, Scotland, Wales, and Ireland bear the shapes of folds made in the Caledonian orogeny. They shed sediment as they eroded, and a great volume of sand came to rest in the British Isles (then scattered to areas throughout the region). These sandstone masses attracted the attention of early British geologists, who named them the Old Red Sandstone. They proposed that there had been a continent to the west that had entirely worn away, which they called the Old Red Sandstone continent. This continent is now known to have been the Greenland coast of Laurentia.

The Uralian Ocean lapped at Baltica's northeastern coastline. Just before the end of the Paleozoic era, the Ural ocean that had washed the eastern shore of Baltica narrowed and closed forever. Two landmasses—Siberia and Kazakhstan—compressed and lifted the sediments of the Ural ocean basin into the Ural mountains. The Urals still stand today, and mark the eastern boundary of Europe within the Eurasian supercontinent.

Africa faced Baltica across the Tornquist Sea. (Two oceans that later lay between Africa and Europe, at different times, are called Tethys. Earlier versions of Tethys are called Paleo-Tethys, and later versions of it are called Neo-Tethys. No Tethys ocean exists today.) Near the close of the Paleozoic Era (245 m.y.a.), Laurussia united with the single southern supercontinent made up of much of the rest of the world's continents, named Gondwana. This created the Pangea (from the Greek pan, meaning all, and Ge, meaning Earth). The Central Pangean mountains arose from this mighty collision, and deformed the rocks laid down during the Paleozoic in central Europe. These mountains joined to the west with the Mauretanides of West Africa, and the Appalachians and Ouachitas of the eastern and southern United States to form a tremendous mountain range stretching along the equator for more than 4,200 mi (7000 km). The whole mountain range is called the Hercynian Mega-suture.

Piece by piece, continental fragments tore away from Africa's northern and western shores and were crushed into the jagged southern edge of Baltica. The same processes that transported these blocks of Europe also deformed them, often changing the crystalline fabric of the rock so much that the original igneous or sedimentary rock type can only be guessed. Between Africa and Europe, tectonic forces seem to have pushed miniature continental blocks in several directions at once-the reconstructions of this time are still unclear. The violently twisted line followed by the Variscan mountain belt anticipated the Alps and other ranges of modern Europe.

Many important rock bodies, called massifs, formed as parts of the Variscan mountains. Giant, bulbous masses of granite and other igneous rocks solidified to form England's Cornwall; Spain and Portugal's Cantabrian The Matterhorn, 14,690 ft (4,480 m), in Switzerland was carved by alpine glaciers. JLM Visuals. Reproduced by permission. Massif; France's Armorican Massif, Massif Central, and the Vosges; Germany's Black Forest; and the Erzgebirge Mountains on the German-Czech border. The Balkans also contain Variscan-age massifs.


Mesozoic and Cenozoic 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 Laurussia and Gondwana together. 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 Pangaea. 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 sediment-laid down on the shallow-sea bottom-began to accumulate throughout Europe.

Beginning at the close of the Mesozoic era (66 m.y.a.), and continuing through the Cenozoic era to the present day, a complex orogeny 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 sideways 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 can't all fit.


Pleistocene Europe

For reasons not yet fully understood, the 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 eight to twelve thousand years ago, only Greenland and Antarctica remain covered with continent-sized glaciers. But during the last two million or so years, Europe's northern regions and its mountain ranges were ground and polished by masses of water frozen into miles-thick continental glaciers.

This ice age began in Europe when heavy snowfalls accumulated in Scandinavia and northern Russia. As the planet's climate cooled, summer's snowmelt did not remove all of winter's snowfall, and an increasingly thick layer of ice accumulated. Ice built up higher and higher in some areas, and eventually began flowing out from these ice centers. As the ice sheet spread over more of the continent, its brilliant surface reflected the sun's heat back out into space—cooling the climate even more. During several intervals, each lasting hundreds of thousands of years, the European ice sheet covered Scandinavia, northern Russia, all the lands around the Baltic Sea, and the British Isles. Ice caps covered the mountain ranges of Europe. Between these planetary deep-freezes were warm, or interglacial, intervals, some of them hundreds of thousands of years long.

Ice in glaciers is not frozen in the sense of being motionless. It is in constant motion, imperceptibly 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 mountainvalleys 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.

Each time the cooling climate froze the equivalent of an ocean of water into glaciers, the global sea level fell drastically (100 ft [30 m] or more). Southern England became a western promontory of the main European landmass, and the North Sea's seabed lay exposed to the sky. The Adriatic Sea almost disappeared, and its seabed became an extension of the Po River Valley. Sardinia and Corsica were at that time one island, and Sicily became a peninsula of mainland Europe.

Unusual geographic conditions also followed the retreat of the ice sheets. Bare rock was exposed in many areas. Elsewhere unvegetated sediment, deposited by the melting glaciers, lay exposed to the elements. Windstorms removed tremendous amounts of the smaller sized grains in this sediment, and carried it far from where the glacier left it. The wind-blown sediment eventually settled out of the sky and formed layers of silt, called loess ("lurse"). Today, loess deposits form a broad belt in various regions from northern France to Russia, and beyond. These deposits originally must have covered almost all of central and eastern Europe.

Continental glaciation occurred several times during the last 2.2 million years. Geologists do not agree whether the ice will return again or not. However, even if the present climate is merely a warm period between glaciations, tens or hundreds of thousands of years may elapse before the next advance of the ice sheets.


Holocene Europe

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 volcanos (cinder cones) have been excavated to produce frost-resistant road fill.

Europe's heavily industrialized regions developed in their present locations as a result of geologic factors. The industrial districts are centered around places where transportation routes carved by rivers occurred in conjunction with ore deposits and fossil fuels.

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. Smaller earthquakes, floods, and other natural disasters happen every year or so. In historic times, in the Aegean Sea and at Pompeii, Herculaneum, and Lisbon, entire cities have been devastated or destroyed by volcanos, 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.


Britain and Ireland

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.


Iberia

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.


Alpine and related orogenies

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"—formerly parts of Europe—moved in various directions at various speeds throughout the Cenozoic era.

On the western Mediterranean floor, new oceanic lithosphere was created. A subduction 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 craton—the Proterozoicage rocks extending north into Russia.

Europe is also host to isolated volcanos 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.


Resources

Books

Hancock P. L., and B. J. Skinner, eds. The Oxford Companion to the Earth. Oxford: Oxford University Press, 2000.

Winchester, Simon, and Soun Vannithone. The Map That

Changed the World: William Smith and the Birth of Modern Geology. New York: Perennial, 2002.

Periodicals

Hoffman, P., ed. "Stonehenge Blues." Discover 11 (October 1990): 10.

Other

Carius, Alexander, and Kurt M. Lietzmann, eds. Environmental Change and Security: A European Perspective (Contributions to the International and European Environmental Policy). Berlin: Springer Verlag, 2002.

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Archean eon

—The interval of geologic time from 3.8 billion years ago to 2.5 billion years ago.

Baltica

—The oldest part of Europe, made of rocks formed between 3.8 and 2.5 billion years ago, that underlies Scandinavia, the Baltic states, Poland, Belarus, and much of western Russia and Ukraine.

Collisional mountain belt

—A mountain range, like the Alps, caused by one continent running into another continent.

Continental arc

—A volcanic mountain range, such as existed in Europe's geologic past, that forms on the tectonically active edge of a continent, over a subduction zone.

Craton

—The part of a continent that has remained intact since Earth's earliest history, and which functions as a foundation, or basement, for more recent pieces of a continent. Baltica is considered to be a craton to which the rest of Europe is attached.

Fault block mountains

—A mountain range formed by horizontal forces that squeeze a continent, fracturing its crust and pushing some crustal blocks upward to form mountains while others drop down to form valleys.

Hadean eon

—The interval of geologic time from the beginning of Earth (4.65 billion years ago) to 3.8 billion years ago.

Island arc

—An curved row of islands of volcanic origin that develops where two lithospheric plates converge, usually near the edge of a continent, and associated with the formation of a deep trench parallel to the arc as oceanic crust is subducted.

Phanerozoic eon

—The interval of geologic time beginning 570 million years ago, the rocks of which contain an abundant record of fossilized life.

Precambrian

—The combined Hadean, Archean and Proterozoic eons, the first four billion years of Earth's history, and for which there is only a poor fossil record.

Proterozoic eon

—The interval of geologic time beginning 2.5 billion years ago and ending 570 million years ago.

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