98 Fun Facts About Earth Science

Which is the correct order of Earth's layers from the surface inward?

Crust, mantle, outer core, inner core: nobody has drilled beyond the crust, so the deeper layers are mapped from the way earthquake waves speed up, slow down and bend on their way through the planet.

Which Danish seismologist discovered in 1936 that Earth has a solid inner core?

Inge Lehmann noticed faint earthquake waves turning up in the 'shadow zone' behind the core, where none were expected, and reasoned that a solid inner core must be deflecting them.

The boundary between Earth's crust and mantle is named after which scientist?

Mohorovičić, a Croatian seismologist, spotted the boundary as a sudden jump in the speed of earthquake waves; the 'Moho' lies only about 7 km beneath the ocean floor but some 35 km under the continents.

Earth's rotation squashes the planet slightly out of round, flattening it where?

The poles: the spin flings the equator outward by about 21 km, so the summit of Ecuador's Chimborazo, not Everest, is the point on the surface farthest from Earth's centre.

Which German meteorologist proposed the theory of continental drift in 1912?

Alfred Wegener presented continental drift in 1912, noting how the coastlines of Africa and South America fit together; he died on a Greenland expedition in 1930, decades before the theory was accepted.

Which supercontinent held nearly all of Earth's land before it began to break apart in the age of the dinosaurs?

Pangaea began to split in the Jurassic, and the widening gaps between its pieces filled with water to become the Atlantic and Indian oceans.

Which US island chain formed as the Pacific Plate slid over a mantle hotspot?

The Hawaiian Islands lie in a line because the plate keeps creeping northwest over the hotspot: each island was carried off in turn, so Kauai is millions of years older than the Big Island.

At which type of plate boundary do plates slide horizontally past each other?

Transform boundaries neither create nor destroy crust: the plates just grind sideways, and along California's San Andreas Fault that slip is slowly carrying Los Angeles toward San Francisco.

What is the volcanic and earthquake belt around the edge of the Pacific nicknamed?

The Ring of Fire is a roughly 40,000 km horseshoe of subduction zones around the Pacific, where oceanic plates dive beneath their neighbours, hosting most of the world's active volcanoes.

Which American cartographer discovered the rift valley running down the Mid-Atlantic Ridge?

Marie Tharp, plotting sonar soundings with Bruce Heezen in 1952, found a continuous rift valley along the Mid-Atlantic Ridge; Heezen first dismissed it as 'girl talk' before the evidence won him over.

Roughly what share of dry air is made up of the second most abundant gas?

The second most abundant gas makes up about 21% of dry air, behind nitrogen's 78 percent; carbon dioxide is only about 0.04 percent.

The ozone layer that absorbs ultraviolet light sits in which layer of the atmosphere?

Because ozone absorbs UV, temperature actually rises with height in the stratosphere, the opposite of the troposphere below it.

In which atmospheric layer do most meteors burn up?

Most meteors burn up in the mesosphere, 50 to 85 km up, where the air is just dense enough to vaporise them; it is also the coldest layer, and the International Space Station orbits above it in the thermosphere.

The Kármán line, the conventional boundary between the atmosphere and space, is at what altitude?

100 km is the round figure the world air-sports federation uses for where the air becomes too thin for wings to work; the United States is more generous, awarding astronaut wings from 80 km.

What is the age of the Earth, according to scientific consensus?

4.54 billion years comes from a meteorite: Earth's own first rocks were recycled long ago, so in 1956 Clair Patterson dated lead from the Canyon Diablo meteorite, which formed along with the planets.

Which is the largest division of geologic time?

The eon is the biggest unit, and Earth has had only four; the first, the Hadean, is named after Hades, the Greek underworld, for the intense heat of the newborn planet.

The Phanerozoic began about 539 million years ago with which geological period?

The Cambrian opened with an 'explosion' of life: in a geologically brief burst, most of the major animal groups alive today made their appearance in the fossil record.

Which geologic epoch began about 11,700 years ago, after the last ice age?

The Holocene is the warm spell since the last glacial period ended, and it has seen all of humanity's recorded history and the rise and fall of every civilisation.

The extinction that wiped out the non-avian dinosaurs happened roughly how many million years ago?

66 million years ago an asteroid at least 10 km wide struck what is now Mexico's Yucatán coast; the debris it threw up darkened the sky, photosynthesis stopped and food chains collapsed.

Carbon-14, used to date organic remains, has a half-life of about how many years?

Carbon-14's half-life of about 5,730 years means too little is left to measure after roughly 50,000 years, so older rocks need slower clocks such as uranium decaying into lead.

The Coriolis effect, which shapes weather systems, is named after a scientist of which nationality?

Gaspard-Gustave de Coriolis was a French mathematician and engineer who described the deflecting force in an 1835 paper on rotating machinery; the effect is far too weak to decide which way a bath drains.

In the Northern Hemisphere, low-pressure systems such as hurricanes rotate in which direction?

Northern Hemisphere lows such as hurricanes spin counterclockwise because the Coriolis effect deflects inflowing air to the right; south of the equator the reverse applies, so Australian cyclones spin clockwise.

Jet streams generally flow in which direction?

Jet streams blow from west to east because Earth's spin deflects air heading for the poles; airlines ride them eastbound to save time and fuel, which is why flying east is usually quicker.

The cloud names cirrus and stratus, coined by the London chemist Luke Howard, come from which language?

Latin cirrus means 'a lock of hair' and stratus 'a spreading', so Howard's names simply describe what each cloud looks like: wispy curls and flat sheets.

Which cloud type produces thunderstorms and can tower all the way to the tropopause?

Cumulonimbus tops flatten into an anvil because the rising air eventually meets air as warm as itself, loses its lift and can only spread out sideways.

El Niño got its name because Peruvian fishermen noticed the warming around which time of year?

Peruvian fishermen noticed the warm current arriving around Christmas, so they called it El Niño, 'the boy', for the Christ child; its cool counterpart La Niña is 'the girl'.

Earth's axis is tilted by about how many degrees, the tilt that gives us seasons?

At 23.4 degrees, the tilt also sets the tropics: the Sun can stand directly overhead only between 23.4 degrees north and south, the Tropics of Cancer and Capricorn.

Which chief librarian of Alexandria worked out Earth's circumference by comparing noon shadows in two Egyptian cities?

Eratosthenes heard that the midsummer noon Sun shone straight down a well at Syene, measured a shadow of one-fiftieth of a circle at Alexandria, and multiplied the distance between them by fifty.

Earth's magnetic field is generated by convection of molten iron and nickel in which layer?

The outer core's churning liquid metal works like a dynamo, and the magnetic field it generates fends off the solar wind, which would otherwise strip away the upper atmosphere.

The magnetic north pole has been drifting from northern Canada toward which region?

Siberia is where it is heading: by 2019 the drift had quickened to about 55 km a year, fast enough that the magnetic model behind navigation systems had to be updated ahead of schedule.

Roughly how long ago was the Brunhes-Matuyama reversal, Earth's most recent magnetic field flip?

Before the flip about 780,000 years ago a compass needle would have pointed south; Motonori Matuyama uncovered such reversals in 1920s Japan by finding old volcanic rocks magnetised backwards.

The green colour of most auroras comes from solar particles exciting which gas?

Oxygen high in the atmosphere gives the green; the same gas glows red in the far thinner air higher still, where its atoms are left undisturbed long enough to release that slower light.

What is the 1859 solar storm that lit auroras worldwide and set telegraphs sparking called?

The Carrington Event is named for Richard Carrington, the astronomer who saw the flare; the air was so charged that some telegraph operators unplugged their batteries and kept sending on the storm's current alone.

Where is most of Earth's fresh water held?

Glaciers and ice caps lock up roughly 69% of all fresh water, with about 30% underground, so every lake and river on Earth shares well under one percent.

The Challenger Deep, the deepest known point in the oceans, lies in which Pacific feature?

The Mariana Trench marks where the Pacific Plate dives beneath a neighbouring plate; its Challenger Deep plunges nearly 11 km, deeper below the waves than Everest rises above them.

The Challenger Deep is named after what?

It takes its name from HMS Challenger, a Royal Navy survey ship whose crew first sounded the deep in 1875, during a voyage around the world that lasted from 1872 to 1876.

Lower sea levels in the last ice age exposed which land bridge, now drowned, between Asia and North America?

Beringia emerged because ice sheets locked up so much water that the sea fell far below today's level, leaving a grassy plain where the Bering Strait is now; people are thought to have walked across.

The periodic variations in Earth's orbit and tilt that drive ice age cycles are named after which Serbian scientist?

Milankovitch calculated how slow wobbles in orbit and tilt change the sunlight reaching the far north; in 1976 seabed sediment cores showed that the ice ages had kept time with his cycles.

Which Swiss-born naturalist, after studying Alpine glaciers, championed the idea that ice sheets once covered much of Europe?

Louis Agassiz read the landscape for clues: scratched, polished bedrock and huge boulders stranded far from where they began convinced him ice had once buried the land; he later became a Harvard professor.

Which planet in the solar system is the densest?

Earth is the densest planet at 5.51 grams per cubic centimetre, just ahead of Mercury at 5.43, thanks to its large iron-nickel core.

Earth's inner core is about as hot as the Sun's surface, so what keeps its iron solid?

Immense pressure, more than three million times that of the air at sea level, packs the iron atoms too tightly for them to melt, however hot they get.

About what share of Earth's surface is dry land rather than ocean?

29% is land and the rest is sea; the Pacific Ocean on its own covers about a third of the planet, enough room to hold every continent with space to spare.

What is the study of rocks, including their formation and composition, called?

Petrology often starts with a sliver of rock ground so thin that light shines through it, so the minerals inside can be told apart under a polarising microscope.

Which foundational principle holds that ancient geological features formed by processes still observable today?

Uniformitarianism, argued by James Hutton and popularised by Charles Lyell, meant that slow everyday processes needed enormous spans of time, pointing to an Earth with, in Hutton's words, 'no vestige of a beginning'.

Which branch of Earth science is the study of groundwater?

Hydrogeology rests on a law the engineer Henry Darcy published in 1856 after measuring water as it seeped through beds of sand: the steeper the pressure drop, the faster the flow.

In the 'spheres' model of Earth science, the pedosphere corresponds to what?

Soil forms only where rock, air, water and living things act on one another, which is why the pedosphere sits at the meeting point of the other four spheres.

Which mineral, the basis of rubies and sapphires, ranks 9 on the Mohs hardness scale, just below diamond?

Corundum sits one step below diamond, but the Mohs scale only ranks which mineral scratches which: in absolute terms diamond is about four times harder than corundum.

Which noble gas is the third most abundant gas in dry air?

Argon is about 0.93% of the air, over twenty times more than carbon dioxide; nearly all of it seeped out of rocks, where radioactive potassium slowly decays into it.

Which continent counts as Earth's largest desert because so little rain or snow falls there?

Antarctica is a polar desert, getting far less precipitation inland than along its coast. Deserts are defined by dryness, not heat, so it outranks the Sahara.

Which pale, lightweight rock is so full of gas bubbles that it can float on water for years?

Pumice forms when frothy lava cools quickly, leaving a rock that can be up to 85% empty space. Rafts of it from undersea eruptions can be a hazard for ships.

Which weather phenomenon briefly heats the air to about five times hotter than the Sun's surface?

Lightning can heat the air it passes through to about 30,000 °C. That sudden heating makes the air expand explosively, which is the shock wave heard as thunder.

Crude oil formed mostly from which ocean organisms, not from dinosaurs as the popular myth claims?

Plankton and algae settled on ancient seabeds, were buried without air, and slowly cooked into oil over millions of years. Heat and pressure deep underground did the cooking.

Which Indonesian volcano erupted in 1883 with the loudest sound ever recorded, heard 4,800 km away?

Krakatoa's blast was mistaken for cannon fire on Rodrigues, an island near Mauritius. Its pressure wave circled the globe more than three times.

Earth's slightly oval orbit brings the planet closest to the Sun during which month of the year?

January brings Earth's closest approach, called perihelion, about two weeks after the December solstice. Seasons come from the planet's tilt, not its distance from the Sun.

Which gas makes up about 78% of the air in Earth's atmosphere, far more than any other?

Nitrogen dominates the air, yet plants cannot take it straight from the sky. Bacteria living with crops such as legumes first 'fix' it into compounds that life can use.

Which soft grey mineral, the so-called lead in pencils, is pure carbon just like diamond?

Graphite was once called black lead because it resembled lead ore, and the name stuck. Pencil cores have never contained any actual lead.

Which coral system, visible from space, is the largest structure on Earth built by living organisms?

Great Barrier Reef corals have built more than 2,900 separate reefs along some 2,300 km of the Queensland coast. The builders are tiny animals called polyps.

Which giant waves, often wrongly called tidal waves, are usually set off by undersea earthquakes?

Tsunamis take their name from the Japanese for 'harbour wave'. Scientists avoid the label 'tidal wave' because tides play no part in causing them.

Which black volcanic glass forms when lava cools too quickly for crystals to grow?

Obsidian breaks with edges so sharp that it was once made into cutting tools. It has even been tried experimentally for surgical scalpel blades.

Which brass-yellow mineral made of iron and sulfur is widely known by the nickname fool's gold?

Pyrite takes its name from the Greek for 'fire', as a stone that strikes sparks. Small quantities of real gold are sometimes found alongside it.

The White Cliffs of Dover are made of which soft rock, built from the skeletons of tiny algae?

Chalk built up on an ancient seabed at perhaps half a millimetre a year. The black streaks running through the white cliff face are bands of flint.

Which dark, fine-grained rock makes up more than 90% of all the volcanic rock on Earth?

Basalt also forms the dark patches visible on the Moon, the lunar maria, which are plains of ancient lava flows.

Purple amethyst, worn by ancient Greeks to ward off drunkenness, is a variety of which mineral?

Quartz turns violet when traces of iron and natural irradiation alter its crystals. The Greek name amethystos refers to the belief that the stone kept its owner sober.

Which mineral, the softest on the Mohs hardness scale, is ground up to make baby powder?

Talc defines hardness 1 on the scale. Ground fine, it also serves as a lubricant and as a filler in paper manufacture.

In a limestone cave, which icicle-shaped formation hangs down from the ceiling as water drips?

Stalactites take their name from the Greek for 'dripping'. The quickest growers gain about 3 mm a year as water leaves calcium carbonate behind.

Which Caltech seismologist gave his name to the earthquake magnitude scale first used in 1935?

Charles Richter developed the scale with his colleague Beno Gutenberg. It was the standard measure of earthquake size until the moment magnitude scale arrived in 1979.

Which 1,200 km California fault divides the Pacific plate from the North American plate?

San Andreas Fault slippage caused the 1906 San Francisco earthquake. The geologist sent to investigate found that the break ran all the way into Southern California.

Which US national park, sitting on a volcanic hotspot, holds well over half of the world's geysers?

Yellowstone explorers named one geyser Old Faithful because it erupted so regularly. The region went on to become the first national park in the United States.

Which island nation straddles the Mid-Atlantic Ridge, one of the few places it rises above the sea?

Iceland is split by the ridge, which runs through Þingvellir National Park, a popular stop for tourists. Nearly all the rest of the ridge lies hidden beneath the Atlantic.

Which process, ongoing beneath the Andes, sends one tectonic plate diving under another?

Subduction recycles old ocean floor back into the planet's interior. The heavier plate is the one that dives, and its slab sinks largely under its own weight.

Which South American country was struck in 1960 by the strongest earthquake ever recorded?

Chile's 1960 quake, centred near Valdivia, is put at magnitude 9.4 to 9.6. Its sea waves crossed the Pacific and devastated Hilo, Hawaii, over 10,000 km away.

Oregon's Crater Lake fills which kind of basin, left when a volcano collapses into its magma chamber?

Caldera comes from the Spanish for 'cooking pot'. Crater Lake's formed about 7,700 years ago when Mount Mazama collapsed, and it holds the deepest lake in the United States.

What are hurricanes called when they form in the northwestern Pacific Ocean, near Japan?

Typhoons, hurricanes and cyclones are the same kind of storm under regional names. The most intense on record, Tip, formed in the northwestern Pacific in 1979.

Which river cut the Grand Canyon, exposing nearly two billion years of Earth's geological history?

Colorado River water is thought to have settled into its course there 5 to 6 million years ago. It kept cutting down as the surrounding plateau was pushed up.

What name is given to the extra-large rise and fall of the sea around every new and full moon?

Spring tides come about twice a month, whatever the season. When the Sun and Moon pull at right angles instead, the weaker neap tides follow.

Which warm Atlantic current flows past Florida and up the US coast before heading toward Europe?

Gulf Stream waters carried Spanish ships home from the Caribbean after Ponce de León's expedition came upon the current. It also helps keep northwest Europe mild.

Which steady easterlies of the tropics have carried sailing ships across the oceans for centuries?

Trade winds blow from the northeast in the Northern Hemisphere and from the southeast in the Southern. Between the two belts lies a zone of calm known as the doldrums.

Which Canadian bay between New Brunswick and Nova Scotia has the highest tidal range in the world?

Bay of Fundy tides can rise and fall by about 16 metres, against a typical ocean range of only one. The funnel-shaped basin makes the water resonate, piling it higher.

Which gas, ahead of carbon dioxide, is the most abundant greenhouse gas in Earth's atmosphere?

Water vapour causes about half of the greenhouse effect, yet it stays in the air for only about nine days. Human activity barely alters its global level directly.

Which 1987 ozone treaty became the first in UN history to be ratified by every country?

Montreal Protocol rules phased out the chemicals that were destroying ozone high in the atmosphere. With 198 parties signed up, the ozone hole is slowly recovering.

Which Hawaiian volcano, the largest active one on Earth, hosts the Keeling Curve's observatory?

Mauna Loa was chosen for tracking carbon dioxide because it is remote, far from any continent and bare of vegetation. The measurements began in 1958.

Which period of the dinosaur age is named after a mountain range just north of the Western Alps?

Jurassic rocks were first identified in the limestone of the Jura Mountains, which gave the period its name. It sits in the middle of the three dinosaur-age periods.

Which rare metal in a thin worldwide clay layer led the Alvarez team to a dinosaur-killing asteroid?

Iridium turned up at hundreds of times its normal level in rocks laid down worldwide just as the dinosaurs vanished. The 1980 finding was led by a father and son.

Which fossil hunter from Lyme Regis unearthed the first two nearly complete plesiosaur skeletons?

Mary Anning was barred, as a woman, from joining the Geological Society of London. Her finds also included the first pterosaur skeleton located outside Germany.

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

Superposition lets geologists rank fossils by age without knowing a single date: in an undeformed stack, whatever lies lowest was buried first.

Which Irish-born naval officer devised a famous scale of wind force in 1805 aboard HMS Woolwich?

Francis Beaufort saw his scale first used on Darwin's voyage aboard HMS Beagle. The captain, Robert FitzRoy, later set up Britain's first Meteorological Office.

Which term for the share of sunlight a surface reflects is high for fresh snow and low for ocean?

Albedo comes from the Latin for 'whiteness'. Fresh snow reflects 90% or more of visible light, while Earth as a whole averages about 30%, helped by its clouds.

Long Island and Cape Cod are built on which ridges of debris dumped at the edge of an ice sheet?

Moraines pile up where the front of a glacier stops advancing and drops the unsorted rubble it has pushed along. Martha's Vineyard and Nantucket formed the same way.

Which American geochemist dated Earth using meteorite lead, then campaigned against leaded petrol?

Clair Patterson found stray lead contaminating everything in his laboratory, even his own hair, as he worked out the dating method. He went on to take on the Ethyl Corporation over leaded fuel.

Which Princeton geologist proposed seafloor spreading after charting the seabed as a navy captain?

Harry Hess kept his transport ship's echo sounder running across the Pacific and found flat-topped undersea volcanoes, which he named guyots.

Which English canal surveyor made the first detailed nationwide geological map of any country?

William Smith, nicknamed 'Strata', worked out his rock sequences in coal mines and canal cuttings. Later ruined financially, he spent time in debtors' prison.

Which durable mineral from Australia's Jack Hills has yielded the oldest dated fragments of Earth?

Zircon crystals carry trace amounts of uranium, whose slow decay into lead gives geologists a built-in clock. That makes it one of the key minerals for dating rocks.

What name is given to the volcanic mudflows that buried the Colombian town of Armero in 1985?

Lahars can set almost as hard as concrete once they stop moving. The word is Javanese, and the 1985 flows from Nevado del Ruiz killed an estimated 23,000 people.

Which University of Chicago meteorologist created the scale rating tornadoes by their damage?

Ted Fujita also discovered downbursts and microbursts. Studying the damage left by the atomic bombs in Japan had shown him how a blast of wind spreads out when it hits the ground.

Which Scottish farmer, often called the father of modern geology, studied the rocks at Siccar Point?

James Hutton concluded from Scottish coasts and crags that landscapes are remade continually over indefinitely long periods of time. He ran two family farms before that.

Which Iowa physicist gave his name to the belts of radiation around Earth confirmed by Explorer 1?

James Van Allen described the belts in a 1958 article after early satellites confirmed them. Similar belts of trapped radiation have since been found around other planets.

Green emerald and blue aquamarine, whose name means sea water, are both varieties of which mineral?

Beryl is colourless when pure, and impurities supply its many colours. Emerald gets its green from about 2% chromium.

Which North Atlantic sea is the only named one without a coast, bounded instead by four currents?

Sargasso waters are named after the brown Sargassum seaweed that floats there. In 1492 Columbus feared that the weed would trap his ship.