50 Fun Facts About History of Earth

Which group of living animals descends from theropod dinosaurs, making its members the only dinosaurs alive today?

Birds evolved from small theropods, the two-legged group that also produced Tyrannosaurus rex. Their closest living relatives are the crocodilians.

About how old is Earth, an age roughly one-third that of the universe itself?

4.5 billion years ago the planet was largely built within 10 to 20 million years, a quick start to a very long story.

Which crater, found by geophysicists prospecting for oil, marks the asteroid strike that doomed the dinosaurs?

Chicxulub lies under about a kilometre of younger rock on Mexico's Yucatán Peninsula, which is why it stayed hidden. The asteroid that blasted it out was roughly ten kilometres wide.

Which supercontinent held nearly all of Earth's land before it began to break apart during the Mesozoic Era?

Pangaea was surrounded by a single superocean, Panthalassa. Its name comes from Greek words for 'all' and 'Mother Earth'.

Which gas, toxic to much early life, did cyanobacteria release into Earth's air as a by-product of photosynthesis?

Oxygen began building up in the air about 2,400 million years ago, a turning point known as the Great Oxidation Event. The gas may have killed off many microbes that had evolved without it.

Which landmass split from Madagascar, drifted north at about 20 cm a year and collided with Asia?

India is still pushing north-east at about 5 cm a year. Its slow-motion crash crumpled the crust into the Himalayas and the Tibetan Plateau.

Which fish, thought to have died out with the dinosaurs 66 million years ago, was caught alive in 1938?

Coelacanth fossils go back more than 410 million years, which made the live catch a celebrated 'living fossil'. A museum curator, Marjorie Courtenay-Latimer, spotted it in a fisherman's haul.

Which rock, laid down on a seabed in the Ordovician Period, forms the very summit of Mount Everest?

Limestone near the summit still holds fragments of sea creatures such as crinoids. The rock formed under water long before the Himalayas began to rise.

Which Ice Age animal survived in the Arctic until about 4,000 years ago, long after Egypt's Great Pyramid was built?

The woolly mammoth had vanished from most of its range by about 10,000 years ago but hung on at Wrangel Island, off Russia's Arctic coast. The island herd died out around 2000 BCE.

Which sea mammals, whose early forms kept hind legs and toes, give Egypt's fossil valley Wadi Al-Hitan its name?

Whales lie fossilised by the hundred at Wadi Al-Hitan, a UNESCO World Heritage Site since 2005. The skeletons record the animals' shift from life on land to life in the ocean.

Which Mars-sized body, named after a Titan of Greek myth, is thought to have struck the young Earth and formed the Moon?

Theia takes its name from the mother of Selene, the Greek goddess of the Moon. Debris thrown out by the collision is thought to have gathered in orbit to build the Moon.

By what nickname is the Permian–Triassic extinction, the most severe in Earth's history, colloquially known?

The Great Dying wiped out most marine species and about 70% of land vertebrate species. Animal life on land took some 30 million years to recover fully.

Which nickname describes the Cryogenian deep freezes, when ice sheets may have spread all the way to the equator?

Snowball Earth was coined by Joseph Kirschvink in 1992. Some researchers prefer a 'slushball', with a band of open water left around the equator.

Which sea dried out almost completely about 5.6 million years ago, leaving a dry basin up to 5 km below sea level?

The Mediterranean refilled about 5.33 million years ago, when the Strait of Gibraltar reopened and the ocean poured back in. Geologists call that deluge the Zanclean flood.

Which eon, when the newborn Earth's surface is thought to have been molten lava, opens the geologic time scale?

The Hadean is named after Hades, the Greek god of the underworld, for its hellish conditions. American geologist Preston Cloud coined the term.

Which era, covering the 66 million years since the dinosaurs died out, is nicknamed the Age of Mammals?

Cenozoic means 'new life', and it is the era still under way. Mammals spread from a few small, simple forms into land, sea and flying animals of every size.

Which epoch, which began about 11,700 years ago, takes in all of written human history?

The Holocene is often called the Age of Humans. It began as the last glacial period ended, and farming, cities and writing all followed.

Which period began about 539 million years ago with an 'explosion' of new animal groups in the fossil record?

The Cambrian explosion lasted between 13 and 25 million years. Charles Darwin counted the sudden appearance of animal fossils among the main difficulties for his theory.

Which period, known as the Age of Fishes, also saw the first forests spread across the land?

The Devonian is named after Devon in south-west England, where its rocks were first studied. Jawed fish became so varied during it that the nickname stuck.

Which period, when giant sauropods were the dominant plant-eaters, is named after mountains on the French–Swiss border?

The Jurassic takes its name from the Jura Mountains, where its rock layers were first identified. Some of its sauropods were the largest animals ever to live on land.

Which layered mounds, built up by mats of microbes in shallow water, still grow at Shark Bay in Australia?

Stromatolites peaked about 1,250 million years ago and then declined, which makes the living mounds of Hamelin Pool a window on a far older world.

Which mineral, found as tiny crystals in Western Australia's Jack Hills, is the oldest known material formed on Earth?

Zircon crystals from the Jack Hills formed about 4,404 million years ago. Their chemistry suggests the young planet already had continental-type crust and liquid water.

Which structures in animal cells carry their own bacteria-like DNA, a relic of microbes that merged with larger cells?

Mitochondria are the 'powerhouses of the cell', and the ancient merger that created them led to every animal, plant and fungus alive.

Which 375-million-year-old fish, found on Ellesmere Island in 2004, had a neck and fins it could prop itself up on?

Tiktaalik is an Inuktitut word meaning 'large freshwater fish', suggested by Inuit elders of Nunavut. It is the earliest known fish with a neck, a step towards four-legged life on land.

Which extinct sea creatures, with over 22,000 described species, lived in the oceans for almost 270 million years?

Trilobites were among the earliest arthropods and among the most successful of all early animals. Only a handful of species remained when the end-Permian extinction finished them off.

Which fuel formed from the vast swamp forests that covered the land during the Carboniferous Period?

Coal gave the Carboniferous its name, which means 'coal-bearing' in Latin. The seams mined today are the buried remains of forests and swamps from about 300 million years ago.

Which volcanic province erupted for roughly two million years and is blamed for the worst mass extinction on record?

The Siberian Traps rank among the largest volcanic events of the last 500 million years. Their eruptions straddled the Permian–Triassic boundary about 252 million years ago.

Which rare metal, found worldwide in clay 66 million years old, led the Alvarez team to propose an asteroid strike?

Iridium is one of the rarest elements in Earth's crust but far more plentiful in rocks from space. The 1980 find showed levels hundreds of times higher than normal.

On which continent have the earliest known Homo sapiens fossils, dated to about 315,000 years ago, been found?

Africa yielded the fossils at Jebel Irhoud in Morocco, a find that pushed the known age of our species back by more than 100,000 years.

Which 3.2-million-year-old skeleton, found in Ethiopia in 1974, showed that upright walking came before bigger brains?

Lucy was named after a Beatles song that played over and over in the expedition camp. The skeleton pairs a small, ape-like skull with signs of an upright, two-legged walk.

Which extinct humans, named after a German valley, vanished about 40,000 years ago but left DNA in people alive today?

Neanderthals interbred with modern humans, as their genome revealed when it was first read from ancient DNA in 2010. The work helped win Svante Pääbo a Nobel Prize in 2022.

Which land bridge, exposed when ice-age sea levels were low, let people walk from Asia into the Americas?

Beringia's land bridge now lies under the Bering Strait and the shallow seas on either side. A small founding population is thought to have lived there during the Last Glacial Maximum before moving on into the Americas.

Which polar researcher proposed in 1912 that the continents slowly drift, an idea geologists rejected until the 1960s?

Alfred Wegener was known in his lifetime mainly as a meteorologist. He died in 1930 on an expedition to Greenland, decades before continental drift won acceptance.

Which process, proposed by Harry Hess and Robert Dietz, forms new ocean crust at mid-ocean ridges and moves it outwards?

Seafloor spreading means the ocean floor itself is on the move, carrying the continents along with it as it spreads from a central rift.

Which lost land joined Britain to mainland Europe until rising seas drowned it between 10,000 and 7,000 years ago?

Doggerland is named after the Dogger Bank, its last high ground to go under. Interest in the lost land took off in 1931, when a fishing trawler dragged up a barbed antler point.

Which objects, formed alongside the planets, did Clair Patterson date in 1956 to work out the true age of Earth?

Meteorites gave Patterson a figure that has stood largely unchallenged ever since. His lead measurements also turned him into a campaigner against leaded petrol.

Which principle, first proposed by Nicolas Steno in 1669, says the oldest rock layers lie at the bottom of the pile?

Superposition lets geologists rank rocks and the remains inside them by age without knowing a single date: lower means older, as long as the layers are undisturbed.

What name do geologists give the remains of short-lived, widespread species used to match rock layers of the same age?

Index fossils show that rocks found far apart formed at the same time, because each species lived only briefly. The best ones were also widespread and quick to evolve.

Which Scottish geologist, a gentleman farmer, concluded from Siccar Point's rocks that Earth must be immensely old?

James Hutton is often called the 'Father of Modern Geology'. He argued that landscapes are never static but are transformed continually over indefinitely long periods of time.

Which radioactive isotope is used to date bone and wood, but only as far back as about 50,000 years?

Carbon-14 starts to dwindle the moment a plant or animal dies, which is what sets the clock. Willard Libby won a Nobel Prize in 1960 for developing the method.

Which metal sank towards the centre of the molten young Earth, where it now makes up most of the core?

Iron is dense enough to sink through lighter material, so it gathered at the centre while silicate rock formed the mantle and crust. Metals that alloy with it readily went down too.

Which rotating cloud of dust and gas flattened into the disc from which the Sun, Earth and the other planets formed?

The solar nebula is the starting point of the standard model of how the Solar System formed. Earth grew inside its disc by accretion, as dust and rock clumped together.

Which fossil bed, discovered by Charles Walcott in 1909, is famous for preserving the soft parts of very early animals?

The Burgess Shale crops out high in the Rockies in Yoho National Park and is about 505 million years old. Walcott went back to its quarry almost every year until 1924.

Which river cut the Grand Canyon, having settled into its course through the area only 5 to 6 million years ago?

The Colorado has sliced down through layer after layer as the land rose, exposing rocks that record nearly 2,000 million years of the past.

Which period, named after hills in South Australia, was ratified in 2004 as the first new one in 120 years?

The Ediacaran holds the oldest definite multicellular organisms with specialised tissues, many shaped like fronds, discs or segmented worms. Geologist Reg Sprigg found such fossils in the Ediacara Hills in 1946.

Which Swiss naturalist, expected to lecture on fossil fish in 1837, instead unveiled his theory of a great ice age?

Louis Agassiz went on to found the science of glaciology. Swiss glaciers were still advancing when he argued that ice had once been far more extensive.

Which fossil hunter from Lyme Regis found the first correctly identified ichthyosaur skeleton at the age of twelve?

Mary Anning also found the first two nearly complete plesiosaur skeletons. As a woman she was not eligible to join the Geological Society of London.

Which Victorian physicist calculated in 1862 that Earth was between 20 million and 400 million years old?

Lord Kelvin worked from how long a hot young planet would take to cool. In 1895 John Perry challenged the figure, questioning its assumptions about how heat is conducted.

Which lost ocean, named after a Greek water goddess, split the northern and southern continents in the dinosaur age?

Tethys was the sister and consort of Oceanus in Greek myth. Fragments of the southern continent drifted north across such seas over 400 million years to build Asia.

Which feature of most modern plants is missing from the fossil record until about 130 million years ago?

Flowers arrived late but took over fast: the plants that bear them diversified explosively and now number about 300,000 known species.