The Stone, Bronze, and Iron Ages

Introduction

Overall Timeline

Early human history can be divided into three ages: stone, bronze, and iron. Note that the dating of these ages is very approximate.

Timeline of the Stone, Bronze, and Iron Ages
ca. 2,500,000 BC-present
1 2 3 4 5 6
1 2 3 4 5 6
Lower Paleolithic
ca. 2,500,000-200,000 BC
Middle Paleolithic
ca. 200,000-50,000 BC
Upper Paleolithic
ca. 50,000-10,000 BC
Mesolithic/Neolithic
ca. 10,000-3000 BC
Bronze Age
ca. 3000-1000 BC
Iron Age
ca. 1000 BC-present

Prehistoric Climate

Throughout its history, the Earth has cycled between cold glacial periods (during which large masses of ice, known as glaciers, cover much of the world's land area) and warm interglacial periods (which lack widespread glaciers). Humans have lived through many such cycles, which take place over thousands of years. While glacial periods made survival more difficult, they also lowered the sea level, easing human colonization of the world. We currently live in an interglacial period, which began ca. 10,000 BC.

Pre-human Evolution

About 14 billion years ago, the Big Bang gave birth to a universe containing pockets of dust. About 4.5 billion years ago, our solar system (the sun and its planets) formed via the accretion of dust into spheres; Earth is therefore roughly 4.5 billion years old. Life began about 3.5 billion years ago, with the appearance of single-celled marine organisms; since then, evolution has continuously given rise to new forms of life.53,54,55

Eventually, multicellular organisms developed. Increasingly large and complex types of multicellular life emerged, with one branch of evolution leading to fish. Fish are the original vertebrates (animals with a backbone) and the ancestors of all other vertebrate groups.

The Five Major Groups of Vertebrates
tetrapod blood reproduction
fish no cold aquatic eggs
amphibians yes
reptiles hard-shelled eggs
birds warm
mammals live birth

Vertebrates made the transition to land-based life when fish evolved into amphibians: cold-blooded tetrapods that lay aquatic eggs. The term cold-blooded denotes that a creature's internal temperature is determined by its environment (in contrast to warm-blooded creatures, whose bodies maintain an internal temperature independent of their environment). A tetrapod is a creature with four limbs; a limb is a jointed appendage that extends from an animal's body. An aquatic egg is laid in water, and thus lacks a hard shell.

Amphibians evolved into reptiles, which lay hard-shelled eggs. Consequently, reptiles were the first vertebrates that could live their entire lives on dry land. The final two major vertebrate groups, birds and mammals, evolved from reptiles.

Some mammals came to abandon a ground-based life, evolving to swing among the trees. This lifestyle encouraged the development of hands with dextrous fingers and opposable thumbs (for grasping branches), as well as sharp colour eyesight (for navigating the complex, multicoloured, shadowy environment of the forest).A3 Sub-Saharan Africa was one region where tree-dwelling mammals thrived.

One day, a species of Sub-Saharan tree-dwelling mammal returned to a ground-based life, leaving the forests behind for open grassland. This animal subsequently evolved to walk upright (rather than on all fours), allowing it to see much farther across the plains. (Animals that walk upright are referred to as bipedal.) When these bipedal mammals started to develop larger brains, they evolved into a remarkable new creature: human.

The Evolutionary Path to Humanity

Main Article

Paleolithic Age

The term human denotes any creature belonging to the genus Homo. The first species of human was Homo habilis, which evolved in Sub-Saharan Africa ca. 2,500,000 BC. Since Homo habilis was a maker of stone tools, the evolution of this species marks the beginning of the stone age.56

The stone age can be divided into the Paleolithic ("Old Stone Age"), during which all humans were hunter-gatherers; the Mesolithic ("Middle Stone Age"), the transitional phase to agricultural life; and the Neolithic ("New Stone Age"), when humans subsisted through agriculture. The Paleolithic, which spans over ninety percent of human existence, can be further divided into three parts.

The Lower Paleolithic was the age of human evolution. Various species of Homo emerged, with a trend toward increasing brain and body size.43 The evolution of modern humans, Homo sapiens, finally took place ca. 200,000 BC, in Sub-Saharan Africa.12

To recap: the Lower Paleolithic period began with the evolution of Homo habilis (the first human species) and concluded with the evolution of Homo sapiens. The latter species was anatomically the same as present-day humans, including (most importantly) brain size.56

Phases of the Paleolithic
Lower Paleolithic early humans behaviourally primitive
Middle Paleolithic modern humans
Upper Paleolithic behaviourally modern

The next giant leap for our species was behavioural modernity (aka "modern behaviour"), which emerged ca. 50,000 BC. Humans of the Lower and Middle Paleolithic exhibited primitive behaviour; though they could make simple stone tools and eventually came to control fire, these humans did not behave much differently than the rest of the animal kingdom. The contrast between humans and animals only became sharp with the onset of modern behaviour.4,56

Behavioural modernity can be boiled down to two major features: complex ideas and creativity. The consequences of behavioural modernity include government, religion, art, and technology.4,56

As noted above, various species of human evolved in Sub-Saharan Africa prior to the evolution of modern humans. Some of these species migrated out of Africa, settling regions of Eurasia. All would eventually go extinct, however, leaving the world to be dominated by a single human species: Homo sapiens.

Modern humans colonized most of the inhabitable world during the Middle and Upper Paleolithic periods. The Americas were colonized by a great migration across the Bering land bridge, which connected Siberia and Alaska.2,22

Neolithic Age

During the Paleolithic age, all humans were hunter-gatherers. They typically lived in small bands that followed an annual migration pattern, timing their movements according to ripening plants and travelling herds of game. Depending on food availability, these bands might be nomadic (constantly on the move) or semi-nomadic (migrating between temporary settlements).K30-31,18

Paleolithic life denotes a lifestyle based mainly on hunting/gathering, while Neolithic life denotes a lifestyle based mainly on agriculture (the production of food by raising domesticated crops and animals). A given region is considered to have progressed to the Neolithic age once agriculture has become the primary means of subsistence.

Means of Subsistence
Paleolithic life hunting/gathering-based life (before ca. 10,000 BC)
Mesolithic life hunting/gathering-based life (after ca. 10,000 BC)
Neolithic life agriculture-based life

Prior to reaching the Neolithic, humans experienced a transitional stage known as the Mesolithic. The transition to agricultural life commenced ca. 10,000 BC, when the most recent glacial period ended, giving rise to a warmer (and thus more farming-conducive) global climate. The beginning of the Mesolithic age is consequently placed at ca. 10,000 BC; the ending, however, varies by region.

As noted earlier, hunting/gathering-based life is also known as Paleolithic life. This is only true up until ca. 10,000 BC, however; the continuation of hunting/gathering-based life beyond ca. 10,000 BC (in the new, warmer climate) is known as Mesolithic life.

Phases of the Stone Age
Lower Paleolithic early humans behaviourally primitive glacial period hunter-gatherer subsistence
Middle Paleolithic modern humans
Upper Paleolithic behaviourally modern
Mesolithic interglacial period
Neolithic agricultural subsistence

Over the final ten millennia BC (ca. 10,000 BC-0), most of the world transitioned to the Neolithic age. The unfolding of this transition can be mapped with very rough approximations for individual regions. For instance, Neolithic life was achieved in Mesopotamia ca. 10,000 BC; in Greece, ca. 7000 BC; in India, ca. 5000 BC; in Britain, ca. 3000 BC.4,18

Diffusion of the Neolithic
Summary of the Spread of the Neolithic
ca. 10,000-5000 BC agricultural life radiates from Mesopotamia, both westward (to Egypt and southern Europe) and eastward (to India)
ca. 5000 BC-0 agricultural life continues to expand, covering most of the inhabited world

As the above map illustrates, Neolithic life radiated from Mesopotamia, both across Eurasia and into North Africa. (It should be noted that while most of Eurasia adopted agriculture as it diffused from Mesopotamia, some regions may have developed agriculture independently.) The diffusion of agriculture to Sub-Saharan Africa, however, was frustrated by the vast Sahara Desert; across this region, agriculture-based life only emerged over the last two millennia BC.4,38,47

In the Americas, Neolithic life was first achieved in Mesoamerica and Peru, but not until ca. 2000 BC. Thus, the rise of Neolithic life throughout the New World was (as in Sub-Saharan Africa) compressed into the final two millennia BC.4,44,46

Alternatives to Farming

Some parts of the world forwent agriculture altogether. In these regions, one of two alternative subsistence methods was pursued.

The first alternative was to continue with hunter-gatherer life indefinitely. This path was followed by Australia, much of Siberia, much of the Americas (the far north and south), and parts of Sub-Saharan Africa. Though hunter-gatherer societies have mostly disappeared in the modern age, a few small populations survive; perhaps most famous are the San people of Sub-Saharan Africa and tribes of the Amazon rainforest.K30-31,4

The second alternative was nomadic herding life. Nomadic herding is well-suited to arid regions, where rainfall is sufficient for grass but too scarce for productive farming; typical herd animals are sheep, goats, cattle, horses, camels (in the Islamic world), and reindeer (in Siberia). Nomadic herding was especially successful in the Steppe (an east-west strip of grassland that runs from Ukraine to Mongolia).48 Like hunter-gatherer life, nomadic herding has been mostly (but not entirely) displaced by the modern age.

The Eurasian Advantage

As described above, the Neolithic age was achieved far earlier in Eurasia than elsewhere. Since Neolithic life was the crucial prerequisite to urbanization, Eurasia experienced the rise of cities thousands of years before the rest of the world. Consequently, Eurasia has given rise to most of the world's civilizations, including the four current "global civilizations": Western, Islamic, South Asian, and East Asian (see Global Civilizations). The modern global political and cultural landscape has been shaped primarily by Eurasia and its colonial offshoots.

Outside Eurasia, the Neolithic age was delayed for various reasons. One is sheer geographic isolation from Southwest Asia, the leading region of early technological progress. While advances in Southwest Asia were transmitted to Europe and Asia relatively quickly, they were blocked from spreading easily to Sub-Saharan Africa (by the Sahara Desert) and the Americas (by the oceans).

Eurasia was also blessed with an exceptional supply of domesticatable plants and animals, in terms of both quantity and quality of species.51 In this context, "quality" denotes usefulness for humans. High-quality domesticated plants are energy-rich and relatively easy to produce; high-quality domesticated animals also have these characteristics, as well as provision of labour and non-food animal products.

The Eurasian advantage in domesticatable animals is particularly striking. Peoples across this region were blessed with goats, sheep, pigs, horses, and cattle (among others); notably, the latter two animals could be harnessed for heavy labour, including ploughing (which amplified farming production) and transportation. In fact, only fourteen large animal species (that is, animals in excess of 100 pounds) have ever been domesticated, and only one of these is native to a region outside Eurasia: the llama, in South America.51

Bronze and Iron Ages

The Neolithic age was succeeded in Eurasia by the bronze age. In a given region, the bronze age is considered to begin when bronze becomes a much-used material for practical objects (i.e. tools and weapons). The term "bronze age" is generally not applied if only a few bronze tools are being made, or if bronze is only being used for jewellery.

The key prerequisite to the bronze age was the development of smelting (the process of extracting metal from ore). Once a sufficient volume of metal has been smelted, it can be hammered or cast (melted and poured into a mould) into a desired shape. Smelting technology first emerged in Southwest Asia.9

The first metal to be smelted was copper. Being a rather soft metal, copper was not a dramatic improvement over stone for the crafting of tools and weapons. It was eventually discovered, however, that by blending copper with tin, one obtains a much harder metal: bronze. (Occasionally, other elements were used instead of tin.)9,50

The bronze age of Southwest Asia spanned ca. 3000-1000 BC. Like agriculture, bronze technology radiated from Southwest Asia in all directions, taking roughly a thousand years to cover the entire east-west span of mainland Eurasia (from Britain to China). Thus, by ca. 2000 BC, most of Eurasia had transitioned to the bronze age.1,26,52 While the bronze age also diffused to North Africa, it was halted by the Sahara Desert.

Spread of the Bronze Age
Bronze Age Transition
Eurasia ca. 3000-2000 BC

The iron age began in Southwest Asia ca. 1000 BC, once smelting pit designs had advanced sufficiently to produce the higher temperatures needed to smelt iron ore (see Iron Smelting).9 In about five centuries, it covered the east-west span of Eurasia. Thus, by ca. 500 BC, most of Eurasia had transitioned to the iron age.27,28

The iron age also diffused across North Africa, and then (unlike the bronze age) southward across sub-Saharan Africa. It crossed the Sahara Desert by travelling down the Nile (through Egypt into Nubia), and may also have crossed at other points farther west. Diffusion was slower than in Eurasia; it took about a thousand years for the iron age to reach southern Africa.38,47

Spread of the Iron Age
Iron Age Transition
Eurasia ca. 1000-500 BC
Africa ca. 1000 BC-0

It should be noted that the above descriptions of the spread of the bronze and iron ages are meant to convey the broad, overall picture. Most likely, these ages did not begin solely in Southwest Asia, but were arrived at independently (at later dates) in other regions as well.

The transition to the iron age was critical not because of any property of the metal itself (iron is not harder than bronze), but rather because iron is overwhelmingly more abundant than copper and tin. This enabled, for the first time in history, true mass-production of metal tools and weapons. Both agriculture and warfare (to take two prominent examples) were thereby revolutionized, since metal implements are far more effective than stone in both endeavours.

The bronze and iron ages have little relevance for the pre-colonial Americas. Prior to the arrival of Europeans, the bronze age was reached only by the Inca (the final Andean civilization), while the iron age did not occur at all.7,33 Gold, silver, and copper were widely used in pre-colonial American art, however.49

1 - "Bronze Age", Encyclopedia Britannica. Accessed April 2009.
2 - "Paleolithic Period", Columbia Encyclopedia. Accessed April 2009.
3 - "Holocene Epoch", Columbia Encyclopedia. Accessed April 2009.
4 - "Stone Age (anthropology)", Encyclopedia Britannica. Accessed April 2009.
5 - "Olduvai Gorge (archaeological site, Tanzania)", Encyclopedia Britannica. Accessed April 2009.
6 - "Metallurgy", Encyclopedia Britannica. Accessed April 2009.
7 - "Bronze Age", Columbia Encyclopedia. Accessed April 2009.
8 - "Abundance of elements in Earth's crust", Wikipedia. Accessed April 2009.
9 - "Smelting (metallurgy)", Encyclopedia Britannica. Accessed April 2009.
10 - "Australopithecus (paleontology)", Encyclopedia Britannica. Accessed April 2009.
11 - "Human Evolution", Columbia Encyclopedia. Accessed April 2009.
12 - "Human Evolution", Encarta. Accessed April 2009.
13 - "Stone Age", Encarta. Accessed April 2009.
14 - "Paleolithic Period (anthropology)", Encyclopedia Britannica. Accessed April 2009.
15 - "Origins of agriculture", Encyclopedia Britannica. Accessed April 2009.
16 - "Civilization", Columbia Encyclopedia. Accessed April 2009.
17 - "Wrought Iron (metallurgy)", Encyclopedia Britannica. Accessed April 2009.
18 - "Neolithic Period", Encyclopedia Britannica. Accessed April 2009.
19 - "Bronze (alloy)", Encyclopedia Britannica. Accessed April 2009.
20 - "Pleistocene Epoch", Columbia Encyclopedia. Accessed April 2009.
21 - "Iron Age", Columbia Encyclopedia. Accessed April 2009.
22 - "First Americans: Clovis-First Theory: Rapid Migration", Encarta. Accessed April 2009.
23 - "American Indian: Main", Encyclopedia Britannica. Accessed April 2009.
24 - "Geologic Time: Main", Encyclopedia Britannica. Accessed April 2009.
25 - "Mesolithic Period (prehistoric period): Main", Encyclopedia Britannica. Accessed April 2009.
26 - "Bronze Age", Encarta. Accessed April 2009.
27 - "Steel: History » Primary steelmaking » Early iron and steel", Encyclopedia Britannica. Accessed June 2009.
28 - "History of Europe: The Metal Ages", Encyclopedia Britannica. Accessed June 2009.
29 - "City", Encyclopedia Britannica. Accessed June 2009.
30 - "Paleolithic Art", Encarta. Accessed April 2009.
31 - "Anthropology: The major branches of anthropology » Cultural anthropology", Encyclopedia Britannica. Accessed June 2009.
32 - "Southern Africa", Encyclopedia Britannica. Accessed June 2009.
33 - "Pre-Columbian Civilization", Encyclopedia Britannica. Accessed June 2009.
34 - "Africa", Encarta 2004.
35 - "Central Africa", Encyclopedia Britannica. Accessed November 2009.
36 - "Homo habilis", Encyclopedia Britannica. Accessed November 2009.
37 - "Human evolution", Encyclopedia Britannica. Accessed November 2009.
38 - "Southern Africa", Encyclopedia Britannica. Accessed January 209.
39 - "Copper Processing", Encyclopedia Britannica. Accessed January 209.
40 - "Europe", Encyclopedia Britannica. Accessed January 209.
41 - "Cranial capacity", Wikipedia. Accessed February 209.
42 - "Human evolution", Wikipedia. Accessed February 209.
43 - "Homo erectus", Encarta 2004.
44 - "Archaic culture", Encyclopedia Britannica. Accessed June 209.
45 - "Neolithic period", Encyclopedia Britannica. Accessed June 209.
46 - "Native American", Encyclopedia Britannica. Accessed June 209.
47 - "South Africa", Encyclopedia Britannica. Accessed June 209.
48 - "Primitive culture", Encyclopedia Britannica. Accessed June 209.
49 - "Native Americans of Middle and South America", Encarta 2004.
50 - "History of technology", Encyclopedia Britannica. Accessed June 209.
51 - "Guns, Germs, and Steel: The Fates of Human Societies", Jared Diamond. W. W. Norton & Company, 2005.
52 - "Hand tool: smelting", Encyclopedia Britannica. Accessed June 209.
53 - "Big Bang Model", Encyclopedia Britannica. Accessed June 209.
54 - "Solar System", Encyclopedia Britannica. Accessed June 209.
55 - "Life", Encyclopedia Britannica. Accessed June 209.
56 - "Homo sapiens", Encyclopedia Britannica. Accessed June 209.
A - "A Short History of the World", John M. Roberts.
K - "History: The Definitive Visual Guide", Adam Hart-Davis.