The story of our planet
Gold nuggets, giant crystals and uncut diamonds star in Dynamic Earth, a stunning exhibition that uses cutting-edge technology and thousands of minerals to tell the story of our ever-changing planet.
Dynamic Earth
This highly visual and immersive exhibition explores the story of the Earth's formation, structure and power through extensive displays of Museums Victoria's impressive geology collection in combination with spectacular and interactive multimedia.
How our planet and its satellite formed
Earth and the other planets formed from a cloud of gas and dust 4.5 billion years ago. It is thought that the Moon formed soon after when a massive object collided with Earth and threw a chunk of Earth into space.
After cooling and solidifying, Earth was soon awash with oceans of water produced by chemical reactions in its young crust, and from impacts of icy comets. Earth’s rotation and the gravitational pull of the Moon created tides in these oceans.
How the Moon formed
Over 4.5 billion years ago, a planet-sized body collided with Earth. Although most of the impact was absorbed into the still-molten Earth, the collision threw debris into space. A large section of this debris solidified in orbit around Earth and formed our Moon.
This rock was blasted off the Moon by the impact of a large meteorite. It was captured by the Earth’s gravitational field and fell to Earth. The composition of lunar meteorites is similar to rock samples collected on the Moon by Apollo missions. This meteorite, Da al Gani 400, is kindly loaned by Hank Ebes.
Ancient Earth
The rocks that first formed the Earth’s surface have been destroyed by erosion and plate tectonics. The oldest known crystals are tiny zircons (zirconium silicate) that formed about 4.3 billion years ago in the very early crust of the Earth. They were later eroded and then reformed into sandstones about 3 billion years ago. Today these sandstones are found in Western Australia.
Earth's structure
Planet Earth has layers made of different materials: an outer crust, a mantle and a core at its centre.
The crust is a very thin layer of rock – basalt below the oceans (10 km thick), and granite and sedimentary rocks on the continents (up to 70 km thick). Under the crust is the mantle, a semi-solid layer 2830 km thick. It is composed mainly of silicate minerals such as olivine. We get clues about its composition when molten rock from this layer comes to the surface during volcanic eruptions.
Below the mantle, the outer core is a layer of slow-moving liquid metal. It generates electrical currents as it flows and these create Earth’s magnetic field. Right in the centre of the Earth, the inner core is a solid mass of hot metal reaching over 5000°C.
Related video: Earth’s internal structure
Janet Hergt, University of Melbourne, describes the structure of the Earth from crust to core.
Tectonic plates and earthquakes
The Australian plate is moving northwards at 10 cm per year and in millions of years will crash into Asia.
The Earth’s surface is made up of large plates which are constantly moving, driven by the internal heat of the planet. At the edges of plates, mountains form, volcanoes erupt and earthquakes fracture the crust, creating ever-changing landscapes.
Related video: Earthquakes and their impact
Gary Gibson, ES&S and University of Melbourne, explains why earthquakes happen and how they cause damage.
The Earth’s tectonic plates are 100 to 200 km thick. They consist of the crust and the uppermost part of the mantle (the lithosphere). The plates slide across the more fluid part of the upper mantle (the asthenosphere). Plate boundaries are zones of intense earthquake and volcanic activity.
Related video: Volcanic eruptions and human life
Ray Cas, Monash University, describes the impact of volcanic eruptions on human existence.
The building blocks of our dynamic planet
Rocks and minerals are the building blocks of our dynamic planet. They form the landscape and provide us with valuable resources. By studying rocks and minerals we can better understand the events that shaped and continue to shape the Earth.
Minerals are naturally occurring chemical compounds that have been formed by geological processes. Minerals also provide chemicals that are essential for life on Earth.
Most rocks are mixtures of different minerals. They show remarkable variations in texture and composition, depending on how they formed.
About rocks
Granite is an igneous rock.
Rocks are classified into three main groups. Igneous rocks consist of solidified magma derived from the melting of other rocks. Sedimentary rocks form where mineral grains and rock fragments are transported from their source, then deposited in layers. Metamorphic rocks form when older rocks are changed by heat and pressure.
The Earth is constantly recycling and transforming its rocky crust. The rock cycle explains how geological processes can change a rock from one type to another through geological time. Movements of tectonic plates and erosion are the main forces driving the rock cycle.
About minerals
Almost all minerals are crystalline, which means they are made up of atoms that are arranged in a three-dimensional lattice. Each mineral has different elements present in regular proportions. For example, pyrite has one iron atom for every two sulfur atoms; its chemical formula is FeS2.
There are about 4400 known minerals. Each year about 60–80 new minerals are discovered. They are named after the place where they were discovered, a deserving person, a prominent feature or property of the mineral, its chemical composition, or its relationship to another mineral.
Mineral shapes
If a mineral has space to grow, it will usually form perfect crystals. Otherwise the mineral will consist of an aggregate of many smaller crystals. These aggregates come in a wide variety of shapes known as ‘habits’, which are determined by the conditions under which the mineral formed.
Mineral colours
The colours shown by minerals span the visible spectrum – and beyond. A mineral’s colour sometimes comes from its essential chemical composition, for example, the striking green colour of dioptase is caused by copper. Other factors that colour minerals are small chemical impurities or defects in their crystal structure.
A single mineral may show a range of colours. This usually arises from the effects of small amounts of ‘foreign’ atoms among the main ingredients of the mineral’s crystal structure. For example, fluorite (calcium fluoride) can be purple, green or yellow because of traces of different elements.
Molten rocks on the surface and below
Spectacular volcanic eruptions show that rocks can get hot enough to melt deep in the Earth. Molten rock is called magma; rocks formed from magma are called igneous rocks.
When magma erupts to the Earth's surface, it is known as lava. The rocks that form from cooled lava, such as basalt, are called volcanic. Volcanoes are named after Vulcan, the Roman god of fire.
Most magma solidifies slowly below the Earth’s surface. Rocks formed in this way, such as granite, are referred to as plutonic. As magma cools, crystals form within the rock. The size of crystals in rocks depends mainly on the rate of cooling, so slowly cooling plutonic rocks have larger crystals than volcanic rocks, which cool much faster.
Related video: Eruption of different types of volcano
Jacqueline Miles, Monash University, explains why some volcanoes erupt gently and others explosively.
Magma
The amount of silica (silicon dioxide) in magma determines how easily it moves. For example, magma that forms basalt has about 50% silica and is very fluid when it erupts. Rhyolite magma, with about 75% silica, is very sticky and does not flow easily. Andesite is about 60% silica.
Most igneous rocks contain minerals from six groups– quartz, feldspar, mica, amphibole, pyroxene and olivine. These occur in various combinations, depending on the magma composition, and are used to classify and name igneous rocks. The composition of igneus rocks provides clues to where magma forms in the Earth. Many igneous rocks contain small amounts of unusual minerals that can have useful properties.
Types of lava
Lavas with the same composition can look different. For example, basalt can be very dense or light and full of gas bubbles (as in scoria). Rhyolite can consist mainly of glassy fragments (ignimbrite), or solid glass (obsidian), or frothy glass that is light enough to float (pumice).
Basalt
Basalt is the most abundant volcanic rock in the Earth’s crust. It is made up of tiny crystals of olivine, pyroxene, amphibole and feldspar. Lava that forms basalt erupts at over 1000°C and is very fluid, so it can flow great distances from a volcano.
Granite
Granite is the most abundant igneous rock in the continental parts of the Earth’s crust. There are many different types of granite, but all have been formed by the melting of other rocks. The composition of granite tells us whether sedimentary or other igneous rocks were melted.
Granite is composed mainly of quartz and minerals from the feldspar, mica and amphibole groups. Crystals form slowly because large bodies of granite magma may take over a million years to cool completely. Uplift and erosion may eventually expose the granite at the Earth’s surface.
Gemstones
Some volcanic rocks contain crystals of minerals that are gemstones. Topaz and beryl are found in silica-rich volcanic rocks, while ruby, sapphire and peridot occur in basaltic rocks. Diamond, the most valuable gemstone, crystallises in the Earth’s mantle and is brought to the surface by explosive volcanic eruptions.
Black Smoker
In some volcanically active regions, hot metal-rich springs bubble up from the ocean floor. As the hot water mixes with cold ocean water, metal sulfides crystallise out. These sulfides form chimneys known as ‘black smokers’. Many ore bodies began as metal-rich deposits like this.
The black smoker on display in Dynamic Earth is the largest ever collected. It was dredged from the seafloor, 2000 metres deep, in the Bismarck Sea off Papua New Guinea by a CSIRO expedition. Scientists have found many new species of fish, giant clams, crabs and worms living in the warm water around black smokers.
Rocks eroded, transported and re-formed
Water, wind and ice relentlessly sculpt the Earth’s surface. Many of the planet’s most spectacular landscapes were carved out as rocks were worn down and the fragments washed away. This destruction provides the raw materials that form sedimentary rocks.When the movement slows, the fragments settle out into a layer of sediment.
Over millions of years, vast amounts of material can be removed, transported and deposited. Layers of new sediment form on the sea floor, in lakes and on flood plains, or form dunes.
Sedimentary processes
Wind, flowing water and moving ice cause erosion by picking up and carrying fragments of rocks and minerals. When the movement slows, the fragments settle out into a layer of sediment. Over time the layers compact, and the grains are cemented together to form sedimentary rocks.
Turning sediments into rock
As sedimentary layers accumulate, they become compacted by the weight of the layers above. Water is squeezed out, and the temperature increases. Grains within the sediment are cemented together by chemical reactions to form harder rock. In limestone, shell material may dissolve and re-form new types of calcium carbonate crystals.
Crystals and opals in sedimentary rock
Some soft sedimentary rocks contain the ingredients needed for minerals to crystallise. For example, pyrite and marcasite form crystals in mud that is rich in sulfur, iron and organic matter.
Sedimentary rocks can also form when minerals crystallise from water, especially when evaporation in shallow water concentrates salts. ‘Rock salt’ comes from sedimentary rocks formed in this way. Many deposits of iron and manganese were formed by crystallisation in seawater, and rare boron-bearing minerals crystallise in salt lakes in some regions.
Gem-quality opal forms mainly in sedimentary rocks where the groundwater is rich in silica. Australia produces 90% of the world’s precious opal, mainly white opal. Boulder opal, a beautiful dark variety that forms veins in iron oxide, comes from Queensland. Shells and the bones of dinosaurs and marine reptiles that have been replaced by precious opal are sometimes found.
Fossils in sedimentary rock
Fossils form when the remains of animals or plants are entombed in sediments that later become rock. Fossils allow geologists to determine the age of sedimentary rocks and learn more about the environment where they were deposited.
Heat and pressure create new rocks from old
Within the Earth, rocks can be changed by heat, pressure or both. Minerals in the rocks break down and re-form in different combinations, altering the appearance and properties of the rocks. This process of change is called metamorphism.
There are two types of metamorphism, contact and regional.
Rocks surrounding a mass of magma can become so hot they are ‘cooked’ and new minerals form. This process is called contact metamorphism.
When continents collide, great thicknesses of rocks are buried, compressed and heated. The resulting change affecting large volumes of rocks is called regional metamorphism.
Changing rocks and minerals
Any rock, whether igneous, sedimentary or metamorphic, can be changed through metamorphosis. The minerals that form will depend on the composition of the original rock, the amount of heat and pressure, the fluids available to help crystallisation, and the time for the process to happen.
A rock formed by metamorphism will usually look very different from the original. Rocks with unusual chemical compositions may produce rare and unusual minerals. The number of chemical ingredients in a rock determines the variety of minerals than can form.
Water is squeezed out of pores and cracks in rocks as they are buried and compacted. Water and gas are also released by minerals as they break down during metamorphism. These ‘juices’ may mix and carry chemical ingredients through the rocks, forming a range of interesting minerals.
Regional metamorphism
As rocks become buried deeper in the Earth’s crust, the pressure becomes so great that hot fluid may be squeezed out of them. The pressure and loss of fluid cause new minerals to form, changing the appearance of the original rock.
These changes are illustrated with the rocks in the images above.
Contact metamorphism
When magma comes into contact with a sedimentary rock, its heat makes the rock much harder. Quartz grains in sandstone recrystallise to form quartzite. Limestone made of shell fragments may form a coarse-grained marble. Mudstone changes into dark, fine-grained hornfels.
As well as heating the surrounding rocks, magma can add elements such as fluorine and boron to them. These new ingredients take part in the changes to the rocks caused by heating. If the rocks are layered, each layer will contain a different set of minerals.
Garnets
Garnets are popular gemstones. The different colours are the result of different chemical compositions. There are fourteen different types (or species) of garnets. They are among the most common minerals in metamorphic rocks, and provide clues to the conditions of metamorphism.
Gems in marble
Limestone, which is mainly calcite derived from the shells of marine animals, is changed by metamorphism into coarse-grained marble. Any impurities of sand and clay in the limestone provide extra ingredients to form attractive gem minerals, such as corundum, spinel and lazurite.
Putting rocks and minerals to work
Ores are mineral concentrations from which useful amounts of metals such as gold, copper, iron or nickel can be extracted. Geological processes that form ores usually involve combinations of heat, pressure and the movement of hot solutions.
Australia is the world’s largest exporter of raw and processed coal for steel-making, and it is one of the world’s two largest exporters of iron ore. It is the world’s second largest producer of gold and is pre-eminent in exports of titanium and zircon mineral sands.
Mineral prospecting involves looking for geological clues, often in remote and featureless country. The most obvious ore-bodies have already been found. Today geologists use remote sensing techniques and knowledge of the geology of existing ore-bodies to search for similar formations.
Related video: Australia's mineral resources
Sandra Close, Surbiton Associates, outlines the significance of mining in Australia today.
Metals
Many geological processes, such as the crystallisation of magma and the compression of rocks during metamorphism, produce hot water that dissolves metals and carries them through pores and fractures in rocks.
As conditions change — for example, when the hot water cools — metal-bearing minerals crystallise and form ores. Many metals combine with sulfur to form minerals known as sulfides. Most metals we use are obtained from sulfide ores. Although large crystals of metal sulfide minerals can form in cracks and cavities in rocks, most ores occur as fine-grained mineral mixtures. Broken Hill in New South Wales is home to a large deposit of metal sulfide ore.
Gold
Gold is highly valued because of its rarity, its attractiveness and its properties. It does not tarnish and can be easily shaped. It has been an international currency and symbol of wealth for thousands of years. Countries buy and store bars of gold, known as bullion, as part of their assets. Gold also has many ornamental and practical uses, which add to its value.
Many geological processes, such as the crystallisation of magma and the compression of rocks during metamorphism, produce hot water that dissolves metals and carries them through pores and fractures in rocks. As conditions change — for example, when the hot water cools — metal-bearing minerals crystallise and form hydrothermal ores.
Gold nuggets form deep underground, where hot fluids deposit gold and quartz in reefs. After millions of years of erosion these reefs are exposed, the quartz is broken down and the gold is washed out. Gold is inert so it remains in soil and streambeds, where it can be found – Eureka!
Minerals from the oxidised zone
Colourful and spectacular mineral crystals are rare. Crystal growth needs time, space and a steady supply of chemical ingredients. One place where all this happens is the oxidised zone, where water containing dissolved oxygen and carbon dioxide seeps down through the ground into rocks containing metal sulfide ores, and dissolves them. This creates a rich ‘chemical soup’ that reacts with the surrounding rocks to form an array of different minerals.
One third of all minerals are formed in oxidised zones. They are also indicators of what lies below. When prospectors find minerals in the oxidised zone they know there is a chance of finding a rich ore-body nearby.
Oxidised zones occur throughout the world, but many of the most spectacular ones are in arid regions. Australia has some famous oxidised zones, such as Broken Hill in New South Wales, Dundas in Tasmania and Browns Prospect in the Northern Territory.
Broken Hill minerals
The name ‘Broken Hill’ came from the ragged ridge of black rocks above the sulfide ore. Mining started on the ridge in 1883 and soon uncovered immense riches of silver, lead and zinc. The wealth generated from the mining of this ore-body has contributed significantly to Australia’s economy.
The rich Broken Hill ore-body began as layers of metal sulfide sludge deposited on the ocean floor about 1700 million years ago. Immense movements of the Earth’s crust then squeezed, folded and overturned the layers and the enclosing rocks. Recrystallisation of the ore led to many complex changes in the minerals.
During and after periods of metamorphism, hot solutions moved through fractures and faults that cut the Broken Hill ore layers redistributing elements such as manganese, iron and silver. The many beautiful and unusual minerals that crystallised in these open spaces are much prized by mineral collectors.
The ore at Broken Hill contains a great diversity of minerals. The main ore-body contains sulfide minerals rich in lead, zinc and silver, but there are about 300 more minerals formed by hydrothermal action and weathering. About 20 of these were new to science when they were discovered.
Related video: The minerals of Broken Hill
Bill Birch, Museums Victoria, describes the formation of minerals at Broken Hill and explains why they are so diverse.
Dundas minerals
The Dundas region in Tasmania, Australia is world-famous for a form of the very rare mineral crocoite (lead chromate).
Large specimens of this vivid orange mineral with splinter-like crystals are found at Dundas.
The unusual local geology brings together rocks rich in chromium and quartz veins rich in lead sulfide.
Browns Prospect minerals
Beautiful combinations of malachite (copper carbonate), cerussite (lead carbonate) and pyromorphite (lead phosphate) have been found at Browns Prospect in the Northern Territory, Australia.
Here, groundwater infiltrated a sulfide ore body providing the copper and lead, while the adjacent limestone provided the carbon and phosphorus.
Museums Victoria staff collected some of these specimens from the site.
Resources from the earth
Stones were among the first tools and weapons used by humans. Later, metals became the basis of wealth and the foundation of empires. Ancient history is recorded on tablets of clay and illustrated with mineral pigments. Likenesses of significant people have been preserved in stone and metal monuments and on coins made of precious metals.
Modern society depends on rock and mineral resources. They are essential for the construction of our cities and for power, transport and communications. They enrich us in art, and we wear them as personal adornments.
Aboriginal uses of rocks and minerals
Ochres of different colours were used by Aboriginal people for decorating implements, for body art and are still used today in ceremonies. One of the most widely used ochres was red ochre, which was extensively used on the body.
Very sharp blades, known as Kimberley points, were chipped from stone. Since European contact, glass and ceramics have also been used.
Grinding stones were used to process foods. Fine seeds were placed on a stone with a depression in it and a top stone was used to grind the seeds producing a flour.
Multipurpose tools such as the woomera were made with a combination of wood, resin and stone. The woomera was primarily used for throwing spears. In addition, a piece of quartzite glued into the handle with spinifex resin provided a blade for cutting meat and for chiselling wood.
Related video: Aboriginal use of rocks and minerals
Phillip Batty, Museum Victoria, describes Aboriginal people’s use of rocks and minerals in Central Australia.
High-tech applications of rocks and minerals
The coffee cup and toothpaste we use in the morning, our cars, our electronic gadgets and the windows we gaze through are all derived from minerals.
As well as theses everyday uses, many crystals have unusual properties that can be altered to be useful for high-tech applications. For example, superconductors, lasers, molecular sieves and high-temperature ceramics have been developed from natural crystals.
Related video: Minerals with high-tech applications
Dermot Henry, Museums Victoria, describes applications of minerals in technology today.
Gemstones
Gemstones have been prized for thousands of years for their colour, clarity, rarity, shape and durability. They are made from minerals that form in many different geological situations. Gemstones are cut and polished to enhance their natural beauty and remove imperfections. The smooth facets created in this way help to transmit and reflect light.
Some gemstones are more valuable than others. Depth and evenness of colour are important, and intensely coloured stones are especially sought after. A gemstone’s colour depends mainly on its chemical composition. In some gemstones the main element causes the colour; for example, turquoise – copper phosphate – is coloured blue by the copper. In other gemstones, very small amounts of an element cause the colour.
Related video: Gem chemistry
Dermot Henry, Museums Victoria, explains the colour and other natural qualities of gemstones.
Museums Victoria’s collection of faceted gemstones and polished ornamental rocks has been acquired since the 1860s. New discoveries mean there are many more minerals used as gemstones now than in the past. Significant contributions to the gemstone collection have been made recently by Peter Hoppen, Murray Thompson, Ron Perrin and Grant Hamid.
Related video: What to look for in a gem
Grant Hamid, Hamid Brothers, describes the diversity of gems and the features that make them special.
Diamonds
Diamond is a form of crystalline carbon and is the hardest mineral on Earth. Diamonds crystallise in the mantle and are brought rapidly to the surface by volcanic eruptions. An old volcanic ‘pipe’ at Argyle in Western Australia provides unusual champagne (pink to brownish) gem diamonds. The ‘four Cs’ – carat, colour, clarity and cut – determine the value of a stone.
The Argyle Diamond Mine, in the East Kimberley region of Western Australia, is one of the world's largest diamond producers. The deposit was discovered in 1979 and mining commenced in 1983. About 5% of diamonds produced by Argyle are high-quality gem, 70% are near gem and 25% are industrial grade.
Ancient rocks from outer space
Meteorites are rocks from space that strike the Earth’s surface. Giant meteorites can have catastrophic effects: huge craters, bomb-like destruction and mass extinctions of species. Such massive impacts occur on average once every 100 million years, but smaller ones much more frequently.
Most meteorites come from the asteroid belt between Mars and Jupiter. Some very rare meteorites are fragments of the Moon, Mars or comets.
Studying meteorites is an easy way of doing space research, because they come to us! Meteorites can help us understand how the solar system formed and may even give clues to the origins of life.
Types of meteorite
Thousands of rock fragments enter Earth’s atmosphere every year from space, but most burn up before impact. Those that strike the surface are very hard to recognise, but most are dark, dense and magnetic. Their surface may be a thin glassy crust or have a rusty and dimpled appearance.
Most meteorites are fragments of asteroids. They are grouped according to composition into stony, stony iron and iron meteorites; about 95% of all meteorites are stony. Meteorites are also classified according to their origin. Those that have not been molten are called chondrites, and those that have been molten are called achondrites.
Evidence of an impact
A very large meteorite striking the Earth blasts itself to pieces and excavates a crater. The impacted rocks may melt and splash over a wide area, or form an impact breccia (suevite) within the crater. Shock waves from the impact leave ripple marks (shatter cones) in the surrounding rocks.
Related video: Accounts of meteorite impacts
Tanya Hill, Museums Victoria, talks about meteorite impacts on Earth including some eyewitness accounts.
Tektites
About 800 000 years ago a large meteorite ploughed into South East Asia. The impact splashed molten glass over the region, including Australia. These glassy blobs, called tektites, were shaped by their rapid flight through the atmosphere. Tektites are associated with impact craters in four distinct regions of the world.
Australites formed by the South East Asia impact rained down like hailstones across Australia. Some australites from Port Campbell in Victoria have perfect button shapes. Because these survived a long journey through the atmosphere, NASA used their aerodynamic shape to design the re-entry vehicles for the Apollo missions.
Meteorite sites in Victoria
Although only 16 meteorites have been found in Victoria, several are of scientific significance. Only Murchison was witnessed falling. Because meteorites are best preserved in dry environments where weathering is slower, most of Victoria’s meteorites have been found in the central and north-western parts of the state.
Related video: The Murchison meteorite story
John Lovering describes his excitement at seeing the Murchison meteorite and its scientific significance.
