50 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.