100 Fun Facts About Earth Science

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

From the surface inward the order is crust, mantle, outer core, inner core; the mantle is the thickest layer at about 2,890 km, and the liquid outer core surrounds the solid inner core.

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

Inge Lehmann, a seismologist at the Danish Geodetic Institute, showed in 1936 that P-waves reflecting off a boundary inside the core mean Earth has a solid inner core within the liquid outer core.

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

Croatian seismologist Andrija Mohorovičić identified the crust–mantle boundary in 1909 from a jump in seismic wave speeds; the 'Moho' lies only 5 to 10 km beneath the ocean floor.

What is Earth's mean radius, to the nearest kilometre?

Earth's mean radius is 6,371 km; the equatorial radius is slightly larger at 6,378 km and the polar radius smaller at 6,357 km, because rotation flattens the planet at the poles.

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.

What name is given to the supercontinent that Wegener argued once joined all the continents together?

Wegener himself called it 'Urkontinent'; the theory was only accepted after seafloor spreading was confirmed in the 1960s.

How many major tectonic plates does Earth's lithosphere have?

Most classifications count seven or eight major plates — African, Antarctic, Eurasian, North American, Pacific, South American and Indo-Australian, sometimes split into Indian and Australian — plus dozens of minor plates.

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

At a transform boundary plates slide horizontally past each other, as along California's San Andreas Fault; divergent boundaries build new crust at mid-ocean ridges and convergent ones create subduction zones.

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?

The Kármán line is set at 100 km above sea level, the altitude the FAI adopted as the edge of space because aerodynamic lift becomes negligible there; it is named for engineer Theodore von Kármán.

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

Earth is about 4.54 billion years old; Clair Patterson pinned the figure down in 1956 using lead isotopes from the Canyon Diablo meteorite, after Lord Kelvin had guessed as little as 20 million years.

Which is the largest division of geologic time?

The eon is the largest formal division: there are four — Hadean, Archean, Proterozoic and Phanerozoic — with eras, periods, epochs and ages nesting inside them.

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

The Cambrian, named by Adam Sedgwick after Cambria, the Latin name for Wales, opened the Phanerozoic and its Paleozoic era; the eon's three eras are the Paleozoic, Mesozoic and Cenozoic.

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

The Holocene began about 11,700 years ago as the last glacial period ended; it sits in the Quaternary period, and its base is formally defined in a Greenland ice core.

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

The impact-driven extinction 66 million years ago marks the Cretaceous–Paleogene boundary; the end-Permian extinction about 252 million years ago was even deadlier.

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 limits the method to samples under roughly 50,000 to 60,000 years old; uranium-lead dating handles rocks billions of years old.

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 flow from west to east because Earth's rotation deflects poleward-moving air; Japanese meteorologist Wasaburo Oishi tracked them with balloons in the 1920s, and speeds near 400 km/h have been recorded.

Which English amateur meteorologist introduced the cloud names cirrus, cumulus, stratus and nimbus in 1802?

Luke Howard, a London pharmacist, proposed the Latin names cirrus, cumulus, stratus and nimbus in his 1802 essay on cloud modifications; the International Cloud Atlas recognises ten genera in the troposphere.

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

Cumulonimbus clouds are the towering storm clouds whose anvil tops can reach the tropopause; they bring lightning, hail and heavy rain.

El Niño got its name because Peruvian sailors 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?

Earth's axial tilt is about 23.4 degrees; it varies between roughly 22.1 and 24.5 degrees over a 41,000-year cycle, while Uranus is tipped over at about 98 degrees.

Which Alexandria librarian first calculated Earth's circumference using shadows at Syene and Alexandria?

Eratosthenes, chief librarian at Alexandria around 240 BC, compared the Sun's shadow angles at Syene and Alexandria to get about 250,000 stadia, remarkably close to the true 40,075 km; he also coined 'geography'.

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

Convection of molten iron and nickel in the outer core drives the geodynamo; the field it produces is only 25 to 65 microtesla at the surface, weaker than a fridge magnet.

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

James Clark Ross first reached the pole in 1831 on Canada's Boothia Peninsula; in the 1990s its drift accelerated to roughly 50 km a year, carrying it across the Arctic Ocean toward Siberia.

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

The Brunhes–Matuyama reversal about 780,000 years ago was the last full flip; reversals come at irregular intervals, and the field deflects most of the solar wind that would otherwise erode the upper atmosphere.

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

Atomic oxygen around 120 km emits the familiar green line at 557.7 nm; oxygen higher up gives red, and nitrogen at the lower edge gives blue and purple.

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

The Carrington Event of September 1859, named for astronomer Richard Carrington who observed the flare, drove auroras as far south as the Caribbean and sent sparks through telegraph lines.

Roughly what percentage of Earth's water is salt water?

About 97.5% of Earth's water is salt water in the oceans and saline groundwater; of the 2.5 percent that is fresh, roughly 69 percent is locked in glaciers and ice sheets and 30 percent is groundwater.

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

The Challenger Deep lies at the southern end of the Mariana Trench, east of the Philippines; it bottoms out near 10,935 metres, and the bathyscaphe Trieste made the first crewed descent in 1960.

The Challenger Deep is named after what?

It takes its name from HMS Challenger, a Royal Navy survey ship whose 1872–76 expedition first sounded the deep in 1875; HMS Challenger II confirmed the record depth by echo-sounding in 1951.

The Quaternary ice age, with its warm interglacials, began about how long ago?

The Quaternary began 2.58 Ma — million years ago — when the Gelasian stage was moved into it in 2009; the Last Glacial Maximum came only 20,000 to 26,000 years ago.

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

Milutin Milankovitch, a Serbian engineer and geophysicist, calculated in the 1920s how cycles in Earth's eccentricity, axial tilt and precession change the sunlight reaching high latitudes, pacing the ice ages.

The scientist who presented the theory of ice ages in 1837, after studying Alpine glaciers, was who?

Louis Agassiz delivered his 'Discourse of Neuchâtel' on ice ages in 1837 after studying Alpine glaciers; the Swiss-born naturalist later founded Harvard's Museum of Comparative Zoology in 1859.

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.

The liquid layer that surrounds the solid inner core is roughly how thick?

This liquid iron-nickel layer is roughly 2,260 km thick, extending from about 2,890 km depth down to 5,150 km, where the solid inner core begins.

Roughly what fraction of Earth's surface is covered by ocean?

Ocean covers about 71% of Earth's surface, some 361 million square kilometres, holding most of the planet's 1.386 billion cubic kilometres of water.

In which decade did geologists accept continental drift, after seafloor spreading was confirmed?

Acceptance came in the 1960s: the 1963 Vine–Matthews explanation of magnetic stripes either side of mid-ocean ridges confirmed seafloor spreading, and plate tectonics followed by 1968.

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

Petrology is the study of rocks, their origin, composition and structure; petrography is its descriptive branch that classifies rock types, while mineralogy deals with minerals and their crystal structures.

Roughly what share of the atmosphere's mass lies in the troposphere, its lowest layer?

The troposphere, the bottom 6 to 20 km, holds about 75% of the atmosphere's mass and nearly all of its water vapour; four thinner layers stack above it out to the edge of space.

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

Uniformitarianism, championed by James Hutton and Charles Lyell and summed up as 'the present is the key to the past', lets geologists read Earth's history by studying processes operating now.

Which branch of hydrology is the study of groundwater?

Hydrogeology is the study of groundwater — how it moves through aquifers and how wells draw on it; Henry Darcy's 1856 law describing flow through sand filters is its founding equation.

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

The pedosphere is the soil layer, where rock, water, air and life meet; some models add it and the cryosphere (ice) to the classic four spheres: lithosphere, hydrosphere, atmosphere and biosphere.

On the Mohs hardness scale, which mineral ranks 9, just below diamond?

Corundum, the mineral of rubies and sapphires, is 9 on Friedrich Mohs's 1812 scale, below diamond at 10 and above topaz at 8; each mineral scratches those ranked beneath it.

Roughly what percentage of dry air is argon, the third most abundant gas?

Argon, at roughly 0.92% of dry air, is the third most abundant gas; it is inert and was mostly produced by the radioactive decay of potassium-40 in Earth's crust.

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.