40 Fun Facts About The Rock Cycle

Seabed limestone now caps Mount Everest thanks to which rock-cycle process, driven by colliding continents?

Uplift has carried rock laid down in a shallow sea to the roof of the world: the limestone at Everest's summit still holds broken trilobites and sea lilies.

Which fine-grained volcanic rock makes up both Earth's ocean floor and the dark 'seas' on the Moon?

Basalt accounts for more than 90 percent of all volcanic rock on Earth, and the Moon's dark patches are plains of it that flooded ancient impact basins.

The giant moai statues of Easter Island were mostly carved from which soft rock made of volcanic ash?

Tuff, volcanic ash compressed into soft stone, was used for all but 53 of the 900-plus moai. Nearly 400 statues in various stages of completion still lie at the Rano Raraku quarry.

Which glassy volcanic rock, formed when lava cools too fast for crystals to grow, was chipped into razor-sharp blades?

Obsidian breaks into edges so sharp that it has been tried out as surgical scalpel blades. Neolithic craftsmen traded their bladelets across southern Europe.

Limestone that is heated and squeezed deep underground recrystallises into which rock, used to build the Taj Mahal?

Marble lets light sink a little way into the stone before scattering back out, which gives statues carved from it a lifelike, waxy glow.

Lava that erupts underwater cools into rounded lumps that geologists name after which bedroom item?

Pillows of lava pile up wherever an eruption happens underwater, and thick stacks of them form the upper layer of the crust beneath the oceans.

Which energy source powers the rain and rivers that wear rock down and carry sediment to the sea?

The Sun lifts water from the oceans by evaporation, so every raindrop and river that carves rock runs on solar energy. Heat from inside Earth powers the melting side of the rock cycle.

Which black sedimentary rock began as swamp plants that were buried, squeezed and heated over millions of years?

Coal is mostly a relic of two geological periods: about 90 percent of all coal beds were laid down in the Carboniferous and Permian, when wetland forests covered the tropics.

Heat and pressure usually destroy which prized finds, making sedimentary rock the best place to hunt?

Fossils survive in sedimentary rock because it forms at temperatures and pressures gentle enough to spare them, which is why its layers are the main record of the history of life.

Which hard, speckled rock, formed from magma that cooled slowly underground, makes up Yosemite's El Capitan?

Granite forms the sheer face of El Capitan, a pale monolith about 3,000 feet from base to summit that solidified roughly 100 million years ago.

Erratics, boulders stranded far from any matching bedrock, were carried there by which agent of erosion?

Glaciers can haul boulders for hundreds of kilometres before melting away and dropping them; Big Rock in Alberta, at 16,500 tonnes, arrived that way.

Rock in high mountains is pried apart mainly by which substance growing inside the cracks?

Ice growing in a crack forces the walls a little further apart with each freeze; geologists rank this frost action as the most important physical way rock breaks down.

Which soft white rock, built from the shells of microscopic sea plankton, forms the White Cliffs of Dover?

Chalk is a limestone made almost entirely of the tiny calcite shells of plankton that sank to the sea floor; matching cliffs face Dover at Cap Blanc-Nez in France.

Which landmark, carved by the Colorado River, exposes nearly two billion years of stacked rock layers?

The Grand Canyon's walls step down from 270-million-year-old limestone at the rim to rock about two billion years old in the Inner Gorge.

Which landform builds up where a river slows and drops sediment, as at the mouths of the Nile and Mississippi?

A delta takes its name from the Nile's mouth, whose triangular outline matches the Greek capital letter; Herodotus noted that Ionian Greeks already called it the Delta.

Which cave formations hang from limestone ceilings like stone daggers, built up by dripping mineral-rich water?

Stalactites grow as each drip leaves a trace of calcium carbonate behind, and even the fastest lengthen by only about 3 mm a year.

About two-thirds of the world's volcanoes, active or dormant, stand in a belt around the rim of which ocean?

The Pacific is ringed by places where ocean floor sinks back into the mantle, a belt that also produces about 90 percent of the world's earthquakes.

Shale squeezed by gentle metamorphism becomes which fine-grained rock, long split into roof tiles and blackboards?

Slate splits into smooth, flat sheets, which is why it has also long been used as the bed beneath the cloth of billiard tables.

Which frothy volcanic rock is light enough to float, sometimes drifting across oceans in vast rafts?

Pumice can be up to 85 percent empty space, and after Krakatoa exploded, rafts of it drifted through the Indian Ocean for up to 20 years.

Which rock-cycle process breaks rock down where it sits, unlike erosion, which carries the pieces away?

Weathering attacks rock in place through water, air and living things; erosion only begins once wind, water or gravity move the pieces.

Which term for igneous rocks formed deep underground comes from the Roman god of the underworld?

Plutonic rocks cool slowly far below the surface and grow coarse crystals, while volcanic rocks take their name from another Roman god, Vulcan.

Rainwater absorbs a gas from the air to become which kind of weak acid, the one that hollows limestone into caves?

Carbonic acid forms when rain absorbs carbon dioxide; feeble as it is, it seeps down fissures and dissolves limestone into caverns and sinkholes.

Sedimentary rock is laid down in visible layers that geologists call by which Latin name?

Strata is the plural of stratum, and reading the order of these layers is the main way geologists have pieced together the history of Earth.

Which process drags old ocean floor back down into the mantle at deep-sea trenches, recycling rock?

Subduction happens because old, cold ocean floor is slightly denser than the hot mantle layer beneath it, so the slab sinks under its own weight.

Which process, named from the Greek for rock, squeezes and glues loose sediment into solid stone?

Lithification destroys the pore space in sediment: burial packs the grains together and squeezes out trapped water, then dissolved minerals cement them.

Which Scottish farmer and physician, called the father of modern geology, argued that rock is endlessly remade?

James Hutton spent some 25 years on his Theory of the Earth, read to the Royal Society of Edinburgh in 1785, which pictured a planet recycling its rocks over immense time.

Sandstone fused by heat and pressure becomes which very hard metamorphic rock, often crushed for highway building?

Quartzite is an interlocking mosaic of crystals so tough that people have shaped it into stone tools since prehistoric times.

New seafloor crust is created as magma rises where plates pull apart, along which undersea features?

Mid-ocean ridges link up into the longest mountain range in the world, a 65,000 km chain that runs through every ocean and dwarfs the Andes.

Which flaky, mica-rich metamorphic rock takes its name from a Greek word meaning 'to split'?

Schist splits easily into flakes along its layers of glittering mica; one variety, Manhattan schist, is part of the bedrock that anchors New York's skyscrapers.

Which type of metamorphism bakes the rock immediately around a body of hot magma, forming a halo called an aureole?

Contact metamorphism is driven by heat rather than pressure, and the baked zone can reach several kilometres wide around the largest magma bodies.

Which principle, popularised by Charles Lyell, holds that processes shaping rocks today also shaped the distant past?

Uniformitarianism is often summed up as the present being the key to the past; William Whewell coined the word in a review of Lyell's Principles of Geology.

Which term for dark, dense igneous rocks blends the word magnesium with the Latin root for iron?

Mafic rocks are rich in magnesium and iron and make up most of the crust under the oceans, while their pale opposites, the felsic rocks, dominate the continents.

Which law, set out by Nicolas Steno in 1669, says the oldest sedimentary layers lie at the bottom?

Superposition lets geologists read a cliff face like a timeline, with newer material stacked on older, as long as the layers have not been badly deformed.

Which name, from the Greek for 'deep stone', describes a vast igneous mass like the core of the Sierra Nevada?

A batholith forms from magma that cooled far underground and covers more than 100 square kilometres; it only comes to light after tens of millions of years of erosion.

Which term, from the Latin for leaf, describes the thin parallel layering squeezed into many metamorphic rocks?

Foliation develops when a rock is shortened along one direction while it recrystallises, so flat minerals line up at right angles to the squeeze.

Sandstone and shale belong to which family of sedimentary rocks, made from broken fragments of older rock?

Clastic rocks are sorted by the size of their grains, from mudrocks made of the finest particles through sandstones up to pebbly rocks made of gravel.

Which igneous rock, named after a South African mining town, carries diamonds up from deep in the mantle?

Kimberlite takes its name from Kimberley, where a diamond rush that began in 1871 led miners to dig the vast open pit called the Big Hole with picks and shovels.

Which discarded theory, championed by Abraham Werner, held that all rocks crystallised out of an ancient ocean?

Neptunism took its name from the Roman god of the sea, and Werner's teaching at the Freiberg Mining Academy made it the leading view in late 18th-century geology.

Which sequence, named for a Canadian petrologist, sets out the order in which minerals crystallise from cooling magma?

Bowen's reaction series explains why certain minerals keep turning up together in igneous rocks while others are almost never found side by side.

The word igneous, used for rocks born from magma, comes from a Latin word meaning what?

Fire is the root because every igneous rock began as glowing molten material, cooled either slowly underground or quickly after an eruption.