50 Fun Facts About Earth Science

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

The mantle is by far the thickest layer at about 2,890 km, and the outer core is liquid while the inner core is solid.

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

The inner core is a ball of mostly iron and nickel about 1,220 km in radius, sitting inside a liquid outer core about 2,260 km thick.

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

The 'Moho' is spotted by a jump in seismic wave speeds; oceanic crust above it is only 5 to 10 km thick.

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

Its average density of 5.515 grams per cubic centimetre makes it the densest planet in the solar system.

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

He noticed the coastlines of Africa and South America fitted like puzzle pieces; the idea was ridiculed and he died on a Greenland expedition in 1930, decades before it was vindicated.

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?

The count depends on how you define them, and there are many minor plates besides; the fastest move about 160 mm a year, roughly the rate hair grows.

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

Divergent boundaries build new ocean crust at mid-ocean ridges; convergent ones create subduction zones and mountains.

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

It follows the subduction zones where oceanic plates dive beneath their neighbours.

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

Heezen initially dismissed her finding as 'girl talk'; the Library of Congress later named her one of the four greatest cartographers of the 20th century.

Nitrogen makes up about 78 percent of dry air. Roughly what share is the second most abundant gas?

That gas is oxygen; argon is next at 0.93 percent, and 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?

It is also the coldest layer of the atmosphere; 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?

About 75 percent of the atmosphere's 5.15 quintillion kilograms sits in the troposphere, the bottom 6 to 20 km.

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

Clair Patterson pinned it down in 1956 using lead isotopes in the Canyon Diablo meteorite; Lord Kelvin had guessed as little as 20 million years.

Which is the largest division of geologic time?

There are four: Hadean, Archean, Proterozoic and Phanerozoic, and eras, periods, epochs and ages nest inside them.

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

Its three eras are the Paleozoic, Mesozoic and Cenozoic, names that mean ancient, middle and recent life.

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

It belongs to the Quaternary period; the International Commission on Stratigraphy keeps the official chart.

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

It marks the boundary between the Cretaceous and Paleogene periods; the earlier Permian extinction was even deadlier.

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

That limits it to samples under roughly 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 wrote about rotating machinery in 1835; the effect is far too weak to decide which way your bath drains.

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

South of the equator it is the reverse, which is why Australian cyclones spin clockwise.

Jet streams generally flow in which direction?

Japanese meteorologist Wasaburo Oishi tracked them with balloons in the 1920s, and speeds of 400 km/h have been measured.

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

The modern International Cloud Atlas recognises ten genera in the troposphere; fog is just stratus at ground level.

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

They are the largest free-convective clouds and bring lightning, hail and heavy rain.

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

The name means 'the boy', a reference to the Christ child; the cool phase, La Niña, is 'the girl'. Events come every two to seven years.

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

It wobbles between about 22.1 and 24.5 degrees over a 41,000-year cycle, and the Moon helps keep it stable; Uranus is tipped over at 98 degrees.

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

His answer of about 250,000 stadia works out remarkably close to the real 40,075 km, and he coined the word 'geography'.

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

The process is called the geodynamo, and the field it makes is far weaker than a fridge magnet, at 25 to 65 microtesla.

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

It sat at Cape Adelaide on the Boothia Peninsula when first reached in 1831 and was 600 km from Resolute Bay by 2001.

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

Reversals happen at irregular intervals, and the field's main job is deflecting the solar wind that would otherwise strip the ozone layer.

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

Oxygen higher up gives red, and nitrogen at the lower edge gives blue and purple; Galileo coined 'aurora borealis' in 1619.

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

It was the first documented link between auroral activity and electrical disturbances on the ground.

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

Of the 2.5 percent that is fresh, about 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?

It bottoms out at about 10,935 metres; the bathyscaphe Trieste made the first crewed descent in 1960 and James Cameron went solo in 2012.

The Challenger Deep is named after what?

HMS Challenger located it in the 1870s and HMS Challenger II confirmed the record depth by echo-sounding in the early 1950s.

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

Ma means million years ago. The Last Glacial Maximum was 20,000 to 26,000 years ago; Louis Agassiz first put the idea of ice ages to scientists in 1837.

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

Earth has been through at least five major ice ages, including the Cryogenian 'Snowball Earth' episodes.

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

The Swiss-American naturalist later founded Harvard's Museum of Comparative Zoology.

Which planet in the solar system is the densest?

Its average density is 5.515 grams per cubic centimetre, thanks to that iron-nickel core.

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

It surrounds the solid inner core, and its churning is what generates the planet's magnetic field.

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

The planet holds about 1.386 billion cubic kilometres of water in total.

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

Paleomagnetic stripes on the ocean floor either side of the ridges provided the proof Wegener never had.

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

Petrography is its 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?

Above it come the stratosphere, mesosphere, thermosphere and exosphere; the whole mix is about 78% nitrogen, 20.9% oxygen and 0.92% argon.

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

It lets earth scientists read the planet's long history by studying how its processes operate in the present.

Which branch of hydrology is the study of groundwater?

People were tapping groundwater by 3000 BC, but the science itself only developed from the 17th century.

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

Some add it and the cryosphere (ice) to the classic four: lithosphere, hydrosphere, atmosphere and biosphere.

Atmospheric chemistry expanded significantly in the 1970s in response to which environmental problem?

The field had begun in the 20th century to measure air pollution, while meteorology dates from late-19th-century weather forecasting.

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

Water vapour and CO2, present in far smaller amounts, do the heavy lifting of trapping the Sun's energy through the greenhouse effect.