40 Fun Facts About Carbon Cycle

Where was carbon, the fourth most abundant element in the Universe, first forged before any of it reached Earth?

Inside stars, helium nuclei fuse into carbon through the triple-alpha process, which runs only in giant and supergiant stars. NASA calls carbon the backbone of life on Earth.

Which British Isles landmark is built from the skeletons of tiny algae that locked carbon away in an ancient sea?

The White Cliffs of Dover are chalk, laid down as white mud on a Late Cretaceous sea floor at about half a millimetre a year. They now stand up to 110 metres tall.

Which planet's carbon dioxide atmosphere traps so much heat that the surface is hot enough to melt lead?

Venus has an atmosphere that is 96.5% carbon dioxide, which holds its surface near 467 °C, hotter even than Mercury. On Earth the carbon cycle keeps most carbon out of the air.

Which fuel, cut from bogs and dried in rural Ireland, holds more carbon worldwide than all forests combined?

Peat stores up to 550 billion tonnes of carbon while covering just 3% of the land surface. It builds up where waterlogged ground stops dead plants from decaying fully.

Which thawing Arctic layer holds about twice as much carbon as the entire atmosphere, locked in plant remains?

Permafrost in the far north holds an estimated 1,400 to 1,650 billion tonnes of carbon, built up over thousands of years. As it thaws, microbes turn part of that store into greenhouse gases.

Which gemstone is pure carbon, crystallised under enormous pressure 150 to 250 km down in Earth's mantle?

Diamond finds at Juina in Brazil showed that the carbon cycle reaches the lower mantle, because the stones held traces of melted ocean crust. A few come from 800 km down.

Which fossil fuel formed from swamp forests that covered the tropics about 300 million years ago?

Coal gave the Carboniferous period its name, which means 'coal-bearing'. About 90% of all coal beds were laid down in that period and the Permian that followed.

Which gas, given off by cattle, rice paddies and swamps, traps far more heat per molecule than carbon dioxide?

Methane has around 80 times the warming power of carbon dioxide over 20 years, yet it lasts less than 12 years in the atmosphere. It is also the main ingredient of natural gas.

Unlike plants, which take in carbon dioxide, animals get nearly all the carbon in their bodies from what source?

The food they eat carries carbon that a plant or alga first captured from the air. Organisms that must get their carbon by consuming others are called heterotrophs.

Which ocean drifters capture about as much carbon dioxide as all land plants, despite being 1% of plant biomass?

Phytoplankton account for about half of all the carbon captured by living things each year. Warmer seas could cut their numbers, because they grow best in cool, nutrient-rich water.

Which process, powered by sunlight, removes more carbon dioxide from Earth's atmosphere than any other?

Photosynthesis drives the fast carbon cycle: plants and algae use the Sun's energy to combine carbon dioxide with water into sugars. That cycle shifts between 1,000 and 100,000 million tonnes of carbon every year.

Which process in the cells of animals and plants breaks down sugar for energy and returns CO2 to the air?

Respiration runs in plants as well as animals, so a forest gives back part of the carbon it takes in. Chemically it is the sugar-building reaction of green leaves in reverse.

Which group of organisms, including fungi and bacteria, returns the carbon in dead leaves and animals to the air?

Decomposers such as fungi feed by releasing enzymes onto dead matter and absorbing what dissolves, a habit called external digestion. Fungi lead the work on leaf litter in many ecosystems.

Which chemical reaction do a campfire, a car engine and a forest fire share, turning stored carbon into CO2?

Combustion of fossil fuels is the main reason carbon dioxide in the atmosphere is rising. It releases in moments carbon that took millions of years to accumulate underground.

Which gas do plants release as a waste product when they build carbon dioxide and water into sugar?

Oxygen given off by plants comes from the water they split, not from the carbon dioxide they absorb. Robert Hill's experiments on isolated chloroplasts in 1937 and 1939 pointed to water as the source.

Which simple sugar, with six carbon atoms in every molecule, do green plants build from carbon dioxide and water?

Glucose is the most abundant simple sugar, and plants chain it into cellulose for their cell walls. That makes cellulose the most abundant carbohydrate in the world.

Through which tiny pores, found mostly on the undersides of leaves, does carbon dioxide enter a plant?

Stomata sit only on the lower leaf surface in most tree species. Each pore is bordered by a pair of guard cells that control how wide it opens.

What name do ecologists give plants and algae, the organisms that first capture carbon at the base of an ecosystem?

Producers are also called autotrophs, because they need no living source of carbon or energy. They form the lowest trophic level of an ecosystem.

Which of Earth's spheres holds most of its carbon, some of it locked away for hundreds of millions of years?

The lithosphere, Earth's rocky outer shell, holds more carbon than the oceans, air and living things put together. Some of that store is the buried remains of ancient life.

Which land store holds about 1,500 gigatons of carbon, roughly three times as much as all plants above ground?

Soil can hold its carbon for thousands of years before erosion washes it away or microbes breathe it back into the air. Warmer ground speeds up that release.

What do scientists call a forest, ocean or other store that takes in more carbon than it gives back?

A sink on land and another in the ocean each take up about a quarter of the carbon that human activity emits every year. A store that gives out more than it takes in is a source.

Which sedimentary rock, built largely from sea creatures' shells, holds about 80% of the carbon in Earth's rocks?

Limestone can keep its carbon locked away for hundreds of millions of years. Heat and pressure deep underground turn it into marble, which NASA calls its metamorphic cousin.

Which landforms, the slow carbon cycle's main route back to the air, emit over 100 times less CO2 than fossil fuels?

Volcanoes emit between 130 and 380 million tonnes of carbon dioxide a year. Their fresh lava then gives the slow carbon cycle new rock to work on.

Which change to seawater, nicknamed the evil twin of global warming, is caused by the ocean absorbing CO2?

Acidification has lowered the pH of the ocean surface by 0.1 since 1750, a 30 percent change. Corals, crabs and snails then struggle to build their shells and skeletons.

Carbon dioxide warms the planet by absorbing which kind of radiation given off by Earth's land and oceans?

Infrared energy soaked up by greenhouse gases is sent back out in all directions, and some of it returns to heat the surface. Without that effect Earth would be a frozen -18 °C.

Extra CO2 speeds plant growth only until plants run short of water or which nutrient, a staple of fertiliser?

Nitrogen sets a ceiling on carbon fertilisation, the extra growth plants manage in air richer in carbon dioxide. The nitrogen cycle is another of Earth's major biogeochemical cycles.

From which natural archive do scientists read 800,000 years of past CO2 levels, sealed in tiny air bubbles?

Ice cores from Antarctica show that carbon dioxide and temperature rose and fell together over the past 800,000 years. The deepest drill holes reach more than two miles down.

Since which era, when people first burned fossil fuels on a large scale, has CO2 in the atmosphere kept climbing?

The Industrial Revolution began moving carbon out of the slow cycle and into the fast one. Left alone, NASA notes, that carbon would have leaked out over millions of years.

Which floating fern may have cooled Earth 49 million years ago by blooming across the Arctic Ocean and burying carbon?

Azolla settled on the stagnant sea floor for about 800,000 years, and the carbon it buried may have helped end a hothouse era when palm trees grew at the poles.

On which Hawaiian mountain has an observatory tracked the rise of carbon dioxide in the air since 1958?

Mauna Loa was chosen for its remote location far from continents and its lack of vegetation. Its record is the foundational study of greenhouse gases in the atmosphere.

Which compound, the active ingredient in many antacids, do corals and clams build into shells that lock carbon away?

Calcium carbonate is also the chalky crust that hard water leaves on a tap, and eggshells and pearls are made of it too. On the sea floor it slowly hardens into rock.

Which slow process sees rain that carries dissolved CO2 break down rock and wash carbon towards the sea?

Weathering needs a few hundred thousand years to rebalance the slow carbon cycle after a surge of carbon dioxide. Warmth brings more rain and faster rock decay, so it works like a thermostat.

Which radioactive isotope, made by cosmic rays in the upper atmosphere, lets scientists date ancient wood and bone?

Carbon-14 stops being topped up when an organism dies, so the amount left shows how long ago that was. Willard Libby and his colleagues pioneered the dating method in 1949.

What do oceanographers call the constant shower of dead organisms and waste carrying carbon to the deep sea floor?

Marine snow flakes can grow to several centimetres across and fall for weeks before they reach the ocean floor. They feed animals living far below the reach of sunlight.

Which animal did Antoine Lavoisier seal in an ice-lined chamber to show that breathing is a slow kind of burning?

A guinea pig melted the ice as it breathed, and Lavoisier matched that heat to the carbon dioxide it gave off. Burning carbon in the same chamber produced the same ratio.

Which mountain range, rising for the past 50 million years, cooled Earth by exposing fresh rock that absorbed carbon?

The Himalayas offered so much fresh rock for rain to attack that carbon dioxide levels fell and ice sheets formed. NASA describes the uplift as resetting Earth's thermostat.

What is the name for one tectonic plate sliding beneath another, dragging carbon-rich sediment into the mantle?

Subduction can carry carbon all the way to the lower mantle, more than 660 km down. Carbon buried this way may stay out of circulation for millions of years.

Which American scientist's namesake curve, begun in 1958, gave the first clear evidence that CO2 in the air is rising?

Charles Keeling built the first instrument able to measure carbon dioxide in air samples with reliable accuracy. His curve zigzags upward, dipping each year as plants grow.

Which protein, thought to be the most abundant on Earth, grabs carbon dioxide from the air inside every green leaf?

RuBisCO is slow, fixing only 3 to 10 carbon dioxide molecules a second, so leaves make it in bulk. It accounts for about half the soluble protein in the leaves of most plants.

In which unit do scientists report carbon dioxide in air, a level of about 280 before fossil fuels were burned?

Parts per million counts molecules: a reading of 387 means that 387 of every million molecules of air are carbon dioxide. Scarcer greenhouse gases are counted per billion.