Computers. Smartphones. Jewellery. Skyscrapers. Automobiles. Look around you! Everywhere, you’ll see objects that couldn’t exist without metal. Can you imagine life without this strong, shiny substance?
Even the human body needs metal! It uses cobalt to make red blood cells. Zinc helps the immune system. High levels of mercury and copper can cause major problems. Even your bones need help from one type of metal—calcium!
Well ,they help keep people healthy. People also use metals to build objects that change the world. But where do all those metals come from?
Some metals are found in the Earth’s crust. Cobalt, iron, and nickel are common in nature. So are gold, zinc, tin, copper, and many others. However, it’s uncommon to find many metals in large quantities separate from other materials. More often, metals found in nature are mixed with rocks and minerals.
When metal is mixed into rocks and minerals, it’s called ore. Before using metals, people have to remove them from the ore. This process is called smelting. It involves heating the metal past its melting point. Once melted, the metal can be filtered to remove other materials.
Metals found in nature are brittle. They’re also prone to rust and corrosion. To make stronger, longer-lasting materials, people mix metals and other substances. The result is called a metal alloy.
Do you know of any metal alloys? One of the most common metal alloys is steel. It’s made by combining iron and carbon. Stainless steel is an alloy often used to make eating utensils. It’s a mixture of iron, carbon, chromium, and molybdenum.
Have you ever seen a piece of jewellery made of rose gold? That’s an alloy made of gold and copper. How about a cast-iron skillet? Cast iron is another alloy. It’s a mixture of iron and carbon. Another common alloy is bronze, made from copper and tin.
What items do you use every day that might contain metals? How about metal alloys? Do you ride to school on a bus or other vehicle? It’s likely made of steel. The chairs in your classroom may contain iron, aluminium, or stainless steel. If you use any digital technology, it likely contains gold, silver, copper, or platinum. Once you start noticing all the metal around you, it’s hard to stop!
To answer the question of where metals come from, first, we need to define the word “metal.” Pure metals are basic elements of matter. There are 118 known elements either found in nature or created in the lab. Most of these elements are metals, but there are a small number of nonmetal elements, such as carbon, and a few “in-between” elements, called metalloids.
What Are Metals?
Metals have certain physical properties that distinguish them from nonmetals and metalloids. The most obvious difference is that metals conduct heat and electricity very well. They are typically hard when solid, and have a glossy shine. Another important quality of metals is that they are ductile, which means they can be hammered, or worked, into different shapes. They also can be melted and cast into moulds, or cut with machine tools to create useful objects.
All of the metals that we find on Earth originated billions of years ago inside the ultra-hot environment of the stars, simple hydrogen and helium atoms fused to create heavier elements. After the original stars exploded, dust and gas from the explosion found its way to our local galaxy and was caught up in the making of our solar system. Particles swirling around the new sun clumped together into planets, including Earth.
You might think Earth is a big lump of rock, hard on the outside and soft in the middle—but quite a lot of it is metal. What exactly is metal? Over three-quarters of the chemical elements that occur naturally on our planet are metals, so it’s almost easier to say what metal isn’t.
When we talk about metals, we’re usually referring to chemical elements that are solid (with relatively high melting points), hard, strong, durable, shiny, silvery grey, good conductors of electricity and heat, and easy to work into various different shapes and forms (such as thin sheets and wires). The word metal is quite a broad and vague term, and not something you can define precisely.
When we talk about nonmetals, it ought to mean everything else—although things are a bit more complex than that. Sometimes you’ll hear people refer to semi-metals or metalloids, which are elements whose physical properties (whether they’re hard and soft, how they carry electricity and heat). Chemical properties (how they behave when they meet other elements in chemical reactions) are somewhere in between those of metals and nonmetals. Semi-metals include such elements as silicon and germanium—semiconductors (materials that conduct electricity only under special conditions) used to make integrated circuits in computer chips and solar cells. Other semi-metals include arsenic, boron, and antimony (all of which have been used in the preparation—”doping”— of semiconductors).
Where do metals come from?
Most pure metals, like aluminium, silver and copper, come from the Earth’s crust. They are found in ores solid materials called minerals, usually occurring in rock, from which the pure metal has to be extracted. The properties of pure metals can be improved by mixing them with other metals to make alloys.
How Do You Make Metal?
A lot of the metal on Earth, especially iron, is found in its core. Metal is scattered unevenly throughout the Earth’s crust, mixed with rock and combined with oxygen and other elements. Some types of rock, such as granite, only hold trace amounts of metal. The metal we use to make buildings, computers, cars and trucks, and many other products come from underground deposits of mineral ores containing high concentrations of metal.
The earliest humans discovered small bits of naturally abundant metals, such as copper, tin and gold, which they hammered into ornaments and other objects. They learned to mix metals to create new metals, called alloys, which improved their characteristics. For example, by mixing copper with tin, they created bronze, which is much harder and better for weapons than pure copper. An important metal alloy is a steel, which is iron mixed with small amounts of carbon.
How Metal Alloys Are Made
The first step in making metal alloys starts with mining the ore from the ground. The ore must then be processed to extract the metal from nonmetals, such as rock. The extraction process may include:
- crushing the ore into powder
- heating it to high temperatures
- rinsing it with water or a chemical bath
- filtering the sludge
- precipitating out the liquid
- applying an electric current to break strong chemical bonds
Once the metal has been extracted, it can be used for an enormous number of purposes, from aluminium cans to steel scaffolding, from galvanised roofs to electronic circuits.
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So, where did all these metals come from? Here’s a very simplified explanation:
All elements, including metals, are made of the same stuff: atomic material—electrons, neutrons, and protons. Atoms of different elements can be distinguished from one another by the number of protons they contain. (The number of neutrons and electrons can vary even among atoms of the same element.) For example, a hydrogen atom contains just one proton. A gold atom has 79. This is true of every one of the countless hydrogen and gold atoms in the universe.
If you could find a way to mash 79 hydrogen atoms together into one atom, you’d have an atom with 79 protons, and therefore you’d have a gold atom. And that’s almost exactly what happens… except it happens inside stars.
There’s Gold In Them Than Stars
Roughly 13.7 billion years ago, matter first appeared in the form of atoms of the two lightest elements: hydrogen, with one proton, and helium, with two. They remain, by far, the most abundant elements in the universe.
After many millions of years, that first hydrogen and helium atoms collected in clouds of dust and gases so huge they would have to be measured in light-years (1 light year = 6 trillion miles or 9.5 trillion kilometres). The clouds eventually gave in to their enormous gravity and collapsed, forming the first stars. And stars were atom destroyers—hot enough to break down those hydrogen and helium atoms and fuse the bits back together, remaking them into larger atoms of different, heavier elements.
For example, if you fuse two hydrogen atoms, you have an atom with two protons—or helium. Fuse three hydrogens and you get an atom with three protons—lithium, the first and lightest metal. Fuse three heliums and you get an atom with six protons—carbon. This is what’s happening in all the stars you see in the sky at night. In the massive ones, the process can result in the production of heavier and heavier elements, including metals such as titanium (22 protons), and iron (26 protons). If they’re especially massive, they can produce the heaviest metals, such as gold (79 protons), and uranium (92 protons). This is one of the things stars do, and that’s how all the elements—including all those shiny metals—are formed in nature.
What are metals like?
With so many chemical elements classified as metals, you might think it would be difficult to generalise about them. But that problem is true of pretty much any generalisation: every house is different, but we can still say that houses tend to have doors, walls, windows, and a roof and provide shelter from the weather—and we can all sketch one on paper.
Signs of metal fatigue in a fractured metal teaspoon.
The generalisations we make about metals are:
- They are mostly solid (at everyday temperatures), crystalline (their atoms are stacked up in orderly patterns like cans in a supermarket), hard, strong, and dense (most metals will sink if you drop them in water, for example).
- Metals are malleable (relatively easy to work into new shapes and forms) and ductile (with the right equipment, you can tease them out into long, thin wires). Even so, they don’t wear out quickly or break easily, though they can and do fracture (crack or snap) eventually through repeated stresses and strains because of metal fatigue (a gradually developing weakness).
- Most metals are opaque (unless extremely thin) and shiny and silvery grey (because they tend to reflect all wavelengths of light to the same extent). Some metals are coloured (because they reflect certain light wavelengths better than others); the best-known examples are probably gold (a yellowish colour) and copper (normally reddish, though it turns blue after exposure to air converts it into copper oxide).
- Most metals conduct electricity well (they have a low electrical resistance, in other words) and feel instantly cold to the touch (because they conduct heat well too, carrying heat energy quickly away from your body).
- Metallic elements such as iron, nickel, cobalt, and neodymium (and alloys based on them) power the best magnets; most other metals make such poor magnets that they’re usually thought of as non-magnetic.
What is the band theory?
Metallurgists (scientists who study metals) prefer to explain the properties of metals using a more complex idea called the band theory. You’ve probably learned in school that the electrons in a single, isolated atom are arranged in energy levels (sometimes referred to as shells, sometimes as orbitals—different ideas but they’re broadly talking about the same thing). In a solid, there are lots of atoms sitting next to one another, but they don’t behave as isolated units. Instead, their electron orbitals overlap, forming what are called bands that extend between atoms (they’re molecular orbitals, in other words), and spread across the entire solid.
According to this theory, solids have two bands called the valence band (containing electrons that are involved in bonding) and the conduction band (which allows electrons to move freely through a metal, carrying heat or electrical energy). What distinguishes metals, nonmetals, and semi-metals is the way electrons move between the bands:
- In metals (conductors), the two bands overlap, so when energy (in the form of heat or electricity) is added to the material, electrons are readily promoted from the valence band to the conduction band and carried through the material, giving rise to an electric current or heat conduction.
- In nonmetals (insulators), there is a large “bandgap” between the valence and the conduction band; in other words, it takes a great deal of energy to get an electron from one band to the other. Under normal circumstances, electrons don’t get promoted from the valence band to the conduction band, and the material doesn’t conduct electricity or heat.
- On this theory, semi-metals (such as semiconductors) are midway between metals and nonmetals: they’re effectively insulators with a much lower bandgap than normal nonmetals.
For at least a few million years, human beings and their ancestors used tools made from such materials as wood, bone, and rock, to help make their lives a little easier. It didn’t make their lives that much easier: Homo sapiens have been relatively primitive nomadic hunters and gatherers for almost all of their existence. Then, around 10,000 years ago, they began discovering ways to work with a “new” material: metal.
The first metals used by humans were the ones that early metalsmiths didn’t have to do very much with to make them usable. These are the native metals—metals that occur in nature in a pure state or are naturally mixed with other elements in a way that maintains their usable properties. They include copper, tin, lead, silver, and gold.
Someone might have just found nuggets of these metals in a streambed or the roots of an unearthed tree, and though they were attractive. They may have pounded them with stone hammers and found that they could shape them. That could have led to metals being used in jewellery or ornaments, or to the making of metal tools and weapons like axes, knives, and swords—a vast improvement over the old stone tools. All of this eventually led to people actively searching for more metals, the establishment of mines, trading in metals between different peoples, and the birth of metal industry. However, it happened—it happened in numerous locations all over the world.
Starting around 8,000 years ago, people started discovering that they could alter the metal. They may have discovered it by accident, or perhaps people just got creative, or maybe it was a combination of both. In any case, new processes were developed to alter metals, then to create entirely new ones that didn’t exist in nature at all—with huge improvements in quality. Over the next few thousand years, mining and metalworking became integral to most of the cultures on Earth, and metal became one of the most civilisation-changing substances in human history. Each of these new processes involved fire, and it’s likely that experimentation with one led directly to the next. The most important advancements:
- Annealing. This is simply the process of heating metal until it’s cherry red. This restores the old, brittle metal to its original malleable state, allowing it to be reworked and prolonging its usability. Annealing can be done at relatively low temperatures (copper can be annealed in a campfire). It was first done sometime around 6000 B.C., somewhere in the Middle East, and possibly in Europe and India around the same time.
- Smelting. In this process, metals are melted into a liquid state, offering for much more freedom to shape them into different forms. Metals were first smelted around 5000 B.C., after the development of more advanced pottery kilns, which can produce much higher heats than could be achieved in simple open fires.
- Alloy Production. This is the process of mixing different metals while they are in a molten state. It began around 3300 B.C. (the beginning of the Bronze Age), with the first production of bronze—a mixture of copper and tin that is much harder and more durable than either of its components.
- Extraction. With further improvements in kiln technology and the subsequent ability to achieve higher temperatures, techniques were developed that allowed for the extraction of metals from ore. It was first done with iron in the Middle East around 1500 B.C.—marking the beginning of the Iron Age.
- Smelting, alloy production, and extraction were practised by ancient peoples in Europe, Asia, South America, and as far north as Mexico, but not in the rest of North America, or Australia, until Europeans arrived. These simple processes remain the foundation of what is likely the largest and most successful industry in human history: the metal industry.
The development of civilisation has relied heavily on the discovery of metals. Prehistoric man used metals to build tools and weapons. As our knowledge of metallurgy has developed, metals have played an essential role in the advancement of agriculture, transport and arts and craft – forging the path to today’s modern society.