Early humans needed a knowledge of simple geology to enable them to select
the most suitable rock types both for axe-heads and knives and for the
ornamental stones they used in worship.
In the Neolithic and Bronze Ages, about
5000 to 2500 BC, flint was mined in the areas which are now Belgium,
Sweden, France, Portugal and Britain.
While Stone Age cultures persisted in
Britain until after 2000 BC, in the Middle East people began to mine
useful minerals such as iron ore, tin, clay, gold and copper as early as
4000 BC. Smelting techniques were developed to make the manufacture of
metal tools possible.
Copper was probably the earliest metal to
be smelted, that is, extracted from its ore by melting. Copper is obtained
easily by reducing the green copper carbonate mineral malachite, itself
regarded as a precious stone. From 4000 BC on, the use of clay for
brick-making became widespread. The smelting of iron ore for making of
tools and weapons began in Asia Minor at about 1300 BC but did not become
common in Western Europe until nearly 500 BC.
The classical period
By recognising important surface processes
at work, the Greek, Arabic and Roman civilisations contributed to the
growth of knowledge about the earth. Aristotle, for instance, recognised
erosion and deposition of surface material. Empedocles and Pliny left
descriptions of eruptions at Etna and Pompeii. The early philosophers did
not leave much in the nature of records. Some of the theories put forward
at the time to explain natural phenomena were based more on speculation
than on observations and may seem amusing today.
At about 540 BC, Xenophanes described
fossil fish and shells found in deposits on mountains. Similar fossils
were noted by Herodotus (about 490 BC) and by Aristotle (384-322 BC).
Aristotle believed volcanic eruptions and
earthquakes were caused by violent winds escaping from the interior of the
earth. Since earlier writers had ascribed these phenomena to supernatural
causes, Aristotle's belief was a marked step forward. Eratosthenes, a
librarian at Alexandria at about 200 BC, made surprisingly accurate
measurements of the circumference of the earth by plotting the angles
between the perpendicular and the sun's rays at two locations (Syene and
Alexandria) on the same meridian. This gave him a measure of the earth's
curvature between the two locations. The Arabs recognised the magnetic
properties of magnetite and used it to make crude compasses.
Medieval and renaissance times
Although in the Middle Ages there was no
marked general interest in geology, some advances were made. Authors such
as Isidore of Seville (AD 570-636) and Vincent de Beauvais and Bartholomew
the Englishman, both in the 13th Century, kept alive and developed the
ideas of earlier writers.
Leonardo da Vinci (1452-1519) scientist and
inventor, recognised that fossil shells are the remains of once-living
organisms and that changes had occurred in the relationship between sea
and land. Georg Bauer, also called 'Agricola' (1494-1556) did much to
advance the knowledge of minerals and metal carrying veins. His great work
'De Re Metallica' (1556) gives a clear description of mining and
metallurgy as they were carried out at the time. The illustrations in this
famous book are particularly instructive.
In 1565 in Switzerland, Conrad Gesner
published a fine descriptive and illustrated work with a long Latin title
which meant, in short, "all about fossils, stones and gems". In
England George Owen carried out systematic observations on strata as early
as 1570, but unfortunately his work was not published until 1796.
The seventeenth and early eighteenth
Until the time of Nicholas Steno
(1638-1686), most advances in geological knowledge were in the fields of
mineralogy and mining. Steno studied rocks in the field in a broad
geological way and used direct observation to enable him to reach a number
of useful conclusions.
Particular aspects of sedimentation had
been recognised earlier but Steno was the first to state important
principles about layers of sedimentary rock. He illustrated his theories
with diagrams showing the geological history of Tuscany. He divided the
history into six phases and believed, wrongly, that the six phases were of
In the Eighteenth Century it became popular
among men of culture to record their findings in the natural sciences. The
succession of rocks in the coalfields of England became well documented
and it was believed to apply over a much wider area. In 1719 and 1725 John
Strachey published two interesting illustrated papers showing the order of
rocks in south-west England. He pointed out that, although the coal strata
were all more or less inclined, the overlying rocks lay horizontally
Elsewhere in Europe the first real attempts
to apply systematic subdivisions to the rocks were made by Giovanni
Arduino (1714-1795) in Italy, Johann Lehmann (1719-1767) in Germany and
Peter Pallas (1741-1811) in Russia. Arduino classified the rocks of
Northern Italy into Primitive, Secondary, Tertiary and Volcanic. His
classification was based on the appearance of the rocks and on the
occurrence of fossils.
Lehmann in 1756 distinguished three orders
(a) Those he believed to have been formed when the world was made;
(b) Those formed from sediment deposited in sheets under water;
(c) Volcanic mountains.
Lehmann's work was followed by that of
George Fuchsel (1722-1773) who published in 1762 one of the first
geological maps in his book 'A History of the Earth and the Sea, Based on
a History of the Mountains of Thurinqia'.
Pallas, in Russia, recognised three broad
divisions of mountains and rock groups. He saw that there was clear
evidence of the presence of the sea in former time in some areas and
supposed that the elevation of the mountains was caused by uplift during
what he termed "commotions of the globe".
Geology becomes a science
Development of geology as a separate branch
of science took place in the years between 1775 and 1830. Geologists
commemorate 1775 as the year in which, at a small mining academy at
Freiburg in Germany, geology was first taught by Abraham Werner. Charles
Lyell published the classic textbook, 'Principles of Geology', in
1830-1833. Many basic principles of geology were recognised and described
during this period. Particularly important were those set out by James
Hutton in Scotland. Two other writers of note were William Smith in
England and Georges Curvier in France.
Abraham Werner (1749-1817) was a careful
mineralogist who drew up an excellent system of classification of minerals
based on their properties. He did not travel extensively, but based most
of his geological ideas on the small region around Freiburg with which he
was familiar. Unlike many present-day scientists, Werner published few of
his theories but the ideas presented in his popular lectures were soon
spread throughout Europe by the enthusiasm of his students.
Werner held that rocks such as granite had
formed during the earth's early history by crystallisation in a worldwide
ocean. He concluded therefore that the oldest rocks in any region were
granites and other crystalline rocks. He did not believe that volcanoes
were important in past geological eras. Because of his theory that what
are known today as igneous rocks originated in the sea, Werner and his
followers were called Neptunists.
James Hutton (1726-1797) must be regarded
as the "father of modern geology". A medical graduate of
Edinburgh University, Hutton inherited a comfortable income and took up
farming. He spent a great deal of time examining interesting rock outcrops
in Scotland and Northern England, and presented his ideas to the Royal
Society of Edinburgh in 1785 in a paper entitled "Theory of The
earth". The Royal Society of Edinburgh was at that time the most
active scientific body in the world.
Hutton recognised the importance of
unconformities and pointed out that many igneous rocks clearly intruded
surrounding rocks, and therefore were younger. Because Hutton and his
followers held that igneous rocks came from molten material within the
earth, they were called Plutonists. His friend, the mathematician John
Playfair (1748-1819) publicised Hutton's theories and added further ideas.
Argument between Plutonists and Neptunists
continued until nearly 1820, but eventually the views of the former group
were found to be valid. Several of Werner's best pupils became Plutonists
after becoming convinced by field evidence. Leopold van Buch (1744-1852),
in particular, recognised the extinct volcanoes of Auvergne and described
them correctly, thus making an important step in the recognition of
ancient volcanic activity.
Hutton's most important concept was that of
uniformity - the idea that processes active today were also active in the
past, and thus that all geological phenomena can be understood in the
light of present processes. The concept was developed from earlier ideas
of G.H. Toulmin and became known as "uniformitarianism".
William Smith (1769-1839) is regarded as
one of the greatest of the early geologists. His recognition of
stratigraphical successions based on fossils and his excellent geological
maps mark the beginning of a new era in geology. Despite his scanty
writings, Smith's ideas and maps justify his eminent place in the history
of geology. In 1815 he wrote: "I have, with immense labour and
expense, collected specimens of each stratum, and of the peculiar
extraneous fossils, organic remains and vegetable impressions, and
compared them with others from very distant parts of the island, with
reference to the exact habitation of each, and have arranged them in the
same order as they lay in the earth; which arrangement must readily
convince every scientific or discerning person that the earth is formed as
well as governed, like the other works of its great Creator, according to
regular and immutable laws which are discoverable by human industry and
observation and which form a legitimate and most important object of
By the end of the 18th Century there was
general agreement about the order of formation of the rocks in Europe. The
accepted stratigraphic succession was as follows:
Tertiary and Volcanic,
The establishment of a geological time
In 1822 the local names given by Smith to
many units of the Secondary rocks began to be used in a wider sense and
became the names in use today. W. Phillips and W.D. Conybeare suggested
the name Carboniferous for what were popularly called "coal
The name Cretaceous (creta, chalk) was
introduced by d'Halloy for the chalk rocks of England and France. The
Jurassic System was also named by d'Halloy.
The Jurassic System was the one which
William Smith studied most when he established the principles of
stratigraphy. At about the same time, Baron Cuvier, a French biologist and
geologist, established, in association with Alexander Brongniart, new
standards and methods in stratigraphy, and especially in palaeontology.
Cuvier wrote "the most important consideration ... is to ascertain
the particular strata in which each of the species was found, and to
observe the greater or less resemblance between these fossil species and
those which still exist upon the earth".
Cuvier thought that changes in the fossils
found in rock successions indicated sudden revolutions in which deposition
was halted and living forms were destroyed, being replaced later by newly
created forms. He wrongly believed that only a certain number of species
had ever existed and that those destroyed were always replaced by an equal
number at the end of each period of geological time. Cuvier's
"catastrophic theory" exerted a great influence on geology for
In 1833 Adam Sedgwick, professor of geology
at Cambridge, mapped rocks in Wales which he called Cambrian after the old
Roman name for Wales. At the same time Charles Lyell was suggesting a
subdivision of the Tertiary period based on the relative number of fossils
similar to living forms. His subdivision is still largely accepted. In
Germany von Alberti introduced the name Trias (sic), and in 1835 Roderick
Murchison published his work on the Silurian System.
Murchison's Silurian rocks included some
which Sedgwick regarded as Cambrian. The two, who had been friends, fell
out and each refused to alter his ideas. A solution was finally proposed
by Lapworth in 1879 when he named the Ordovician System. It included the
upper part of Sedgwick's Cambrian and the lower part of Murchison's
Silurian. In 1840, after visiting Russia, Murchison named the Permian
System (Perm in Russia), while the Devonian System (Devon in England) was
named in the same year. About 1855 William Logan in Canada studied rocks
older than the Cambrian and called them the Precambrian System. Thus, by
the middle of the Nineteenth Century, the general geological time scale
based on fossils and stratigraphic mapping was established.
Hutton, Lyell and others recognised that
the principle of uniformitarianism required very long periods of time, and
that the presence of unconformities indicated long time breaks when a
local area was being eroded.
There was, however, considerable opposition
to the geological method of calculating the ages of minerals and rocks,
both from religious authorities and from physicists.
Some of the former based their concept of
the age of the earth on Biblical chronology calculated by Bishop Ussher in
the 17th Century. They thus thought that Creation occurred in 4004 BC.
The physicists, led by Lord Kelvin,
maintained that the earth could not be more than 100 million years old.
They made the assumption that the earth began as a molten mass and was in
process of cooling. The discovery of radioactivity in minerals about 1896
showed that the earth was cooling down at a much slower rate than Kelvin
had estimated and thus his figure for the age of the earth was too low.
Since then techniques based on the breakdown of radioactive isotopes of
uranium, strontium, potassium, carbon and other elements have made it
possible to measure the age of the earth and the extent of each geological
Other geological advances
During the second half of the l9th Century,
while stratigraphic data on various parts of the world were being refined,
many other geological advances were being made.
The science of petrology had its origin
early in the l9th Century in the careful descriptions of rock specimens by
von Buch, Nicol and others. Petrology expanded rapidly after the
development of the petrological microscope. In 1851 in England H.C. Sorby
published the first description of thin sections of sedimentary rocks, and
in 1870 Zirkel described basalts in Germany.
Important advances in the understanding of
the chemistry of rocks followed. Bunsen (of bunsen burner fame) suggested
in 1851 that igneous rocks were derived from two separate magmas,
"acid" and "basic". V.M. Goldschmidt, who collected a
vast amount of data about the distribution of elements in the earth's
crust and interior, may be considered the founder of the science of
geochemistry. At about 1910, Bowen began laboratory studies in
experimental petrology, examining the behaviour of melts of silicates
under various conditions. Similar experimental work is now being widely
carried out with greatly improved equipment which can simulate high
pressures and high temperatures and assist in the study of the complicated
chemical reactions taking part in the deep crust of the earth.
Geomorphological studies were advanced by
the work of Agassiz, who in the 1840s recognised the effects of
Pleistocene glaciation in Europe and the USA. Later Gilbert and Powell
made classical studies on arid erosion in the western USA. The strongest
influence up to 1900 was the work of W.H. Davis, an American who worked
both in USA and Europe and who first defined the cycle of erosion.
Davis pointed out that the landscape was
the product of the underlying structure (rock type, folding, etc.) the
acting processes, and time. Davis concentrated on climatic conditions and
structure, but later geomorphologists have given more detailed attention
to a wide range of processes, including river action and sea erosion.