Counting Backwards from Now
60 years ago - Invention of the computer.
130 years ago - Invention of the telephone.
180 years ago - Fossil fuel revolution: coal, trains.
540 years ago - Invention of the printing press.
5,500 years ago - Invention of the wheel, writing.
7,600 years ago - Sahara desert starts forming in northern Africa.
8,800 years ago - The first cities.
10,300 years ago - End of the most recent glacial period: the Wisconsin glaciation.
12,700 - 11,500 years ago - the Younger Dryas.
18,000 years ago - Cultivation of plants, herding of animals. Homo sapiens arrives in the Americas.
21,000 years ago - Last glacial maximum: ice sheets down to the Great Lakes, the mouth of the Rhine, and covering the British Isles.
32,000 years ago - Oldest known cave paintings.
35,000 years ago - Invention of the calendar, extinction of Homo neanderthalensis. Homo sapiens arrives in Europe.
50,000 years ago - Homo sapiens arrives in central Asia.
100,000 years ago - Homo sapiens arrives in the Middle East.
110,000 years ago - Beginning of the most recent glacial period: the Wisconsin glaciation.
130,000 years ago - Beginning of the Eemian interglacial.
200,000 years ago - Beginning of the 2nd most recent glacial period: the Wolstonian glaciation.
250,000 years ago - First Homo sapiens.
350,000 years ago - First Homo neanderthalensis.
380,000 years ago - Beginning of the Hoxnian interglacial.
450,000 years ago - Beginning of the 3rd most recent glacial period: the Kansan glaciation, during which ice sheets reached their maximum extent in the Pleistocene, down to Kansas and Slovakia.
620,000 years ago - Beginning of the Cromerian interglacial.
1.4 million years ago - First firemaking by humans.
1.9 million years ago - First Homo erectus.
2.5 million years ago - First Homo habilis. Beginning of a period of repeated glaciation (loosely speaking, "ice ages").
3 million years - Cooling trend causes year-round ice to form at the North Pole.
3.9 million years ago - First known Australopithecus afarensis.
5 million years ago - Humans split off from other apes (gorillas and chimpanzees).
21 million years ago - Apes split off from other monkeys.
24 million years ago - Cooling trend causes the formation of grasslands; Antarctica becomes covered with ice.
34 million years ago - Gondwanaland finishes breaking up, with Australia and South America separating from Antarctica.
50 million years ago - India begins to collide with Asia, eventually forming the Himalayas.
67 million years ago - Asteroid hits Mexico, causing the Cretaceous-Tertiary extinction. End of dinosaurs. 50% of all species died out! Intensification of world cooling trend.
114 million years ago - First modern mammals. World begins to cool.
150 million years ago - First birds.
200 million years ago - Pangaea began to split into separate continents: Gondwana to the south and Laurasia to the north, separated by the Tethys Sea.
205 million years ago - The Triassic-Jurassic extinction. End of large amphibians and many reptiles.
235 million years ago - First dinosaurs, flowers.
250 million years ago - The Permian-Triassic extinction. 90% of all species died out! Formation of the supercontinent Pangaea, with surrounding ocean Panthalassa.
313 million years ago - First reptiles.
365 million years ago - The Late Devonian extinction. 70% of marine species died out! First amphibians, trees.
395 million years ago - First insects on land.
415 million years ago - The Old Red Sandstone Continent, also known as Laurussia, is formed by the collision of Baltica and Laurentia at the beginning of the Devonian.
440 million years ago - The Ordovician-Silurian extinction. Most marine species died out.
670 million years ago - First animals.
630-850 million years ago - The Cryogenian Period, also known as Snowball Earth - the worst ice age in the Earth's history.
800 million years ago - The supercontinent Rodinia begins to break up.
1 billion years ago - Formation of the supercontinent Rodinia
1.3 billion years ago - First plants.
1.6 billion years ago - First blue-green algae.
2.4 billion years ago - The Great Oxidation Event: the Earth's atmosphere gets oxygen.
3 billion years ago - Formation of the first known continent, Ur.
3.8 - 4 billion years ago - The Late Heavy Bombardment: a period during which the Earth, Moon, Venus and Mars were subjected to many asteroid impacts, after a relatively calm period of several million years.
4 billion years ago - First life on Earth.
4.45 billion years ago - Formation of Earth complete; storm of asteroid impacts.
4.5 billion years ago - Formation of the Moon: according to the Giant Impact Hypothesis, this happened when Theia collided with proto-Earth.
4.55 billion years ago - Formation of the Solar System.
13.3 billion years ago - Reionization: the first stars heat and ionize hydrogen gas.
13.3 - 13.7 billion years ago - The Dark Ages, after the formation of hydrogen and before the first stars.
13.7 billion years ago - The Big Bang: beginning of the universe as we know it!
Counting Down to the Big Bang
In what follows I give the temperature of outer space in Kelvin at various times. Kelvin means "degrees Celsius above absolute zero". The melting point of water is 273 Kelvin; the boiling point is 373 Kelvin.
13.7 billion years after the Big Bang - Now.
Temperature: 2.726 Kelvin
550 million years after the Big Bang - Reionization:
first stars heat and ionize hydrogen gas.
Temperature: roughly 30 Kelvin.
380 thousand years after the Big Bang - Recombination:
hydrogen gas cools down to form molecules.
Temperature: 3000 Kelvin.
10 thousand years after the Big Bang -
End of the radiation-dominated era.
Temperature: 12,000 Kelvin.
1000 seconds after the Big Bang - Decay of lone neutrons.
Temperature: roughly 500 million Kelvin.
180 seconds after the Big Bang - Beginning of
of helium and other elements from hydrogen
Temperature: roughly 1 billion Kelvin.
10 seconds after the Big Bang - Annihilation of electron-positron pairs.
Temperature: roughly 5 billion Kelvin.
1 second after the Big Bang - Decoupling of neutrinos.
Temperature: roughly 10 billion Kelvin
100 microseconds after the Big Bang - Annihilation of pions.
Temperature: roughly 1 trillion Kelvin
50 microseconds after the Big Bang -
"QCD phase transition": quarks get
bound into neutrons and protons.
Temperature: 1.7-2.1 trillion Kelvin
10 picoseconds after the Big Bang -
"Electroweak phase transition":
electromagnetic and weak force become different.
Temperature: 1-2 quadrillion Kelvin.
Note: a picosecond is a trillionth of a second. Before this the temperatures were so high that our knowledge of physics is unable to say for sure what happened, though experts have some good guesses.
Counting Forwards into the Future
50 thousand years from now - possible end of the Anthropocene Epoch, the period of warm climates caused by the rapid burning of fossil fuels.
50 million years from now - Africa collides with Europe, eliminating Mediterranean sea.
150 million years from now - Atlantic ocean begins to close.
250 million years from now - North and South America collide with Africa, forming a new supercontinent.
750 million years from now - The Sagittarius dwarf spheroidal galaxy makes its next pass through the Milky Way, and perhaps disintegrates.
1.1 billion years from now - The Sun becomes 10% brighter than today. Runaway greenhouse effect may evaporate the Earth's oceans. If so, the water in upper atmosphere will photodissociate and the hydrogen will sail off into outer space.
2 billion years from now - The Andromeda Galaxy approaches our galaxy, the Milky Way:
3.5 billion years from now - The Sun becomes 40% brighter than today. Conditions on Earth resemble those on Venus today.
3.75 billion years from now - The Andromeda Galaxy nears the Milky Way:
3.85 billion years from now - The Andromeda Galaxy makes its first pass by the Milky Way, leading to a burst of star formation:
3.9 billion years from now - Star formation reaches its peak as Andromeda Galaxy makes its first pass by the Milky Way:
4 billion years from now - the Andromeda Galaxy becomes tidally stretched and the Milky Way is warped after their first near-collision:
5.1 billion years from now - the cores of the Andromeda Galaxy and Milky Way will be visible as bright lobes in the sky during their second pass. There will be less star formation, because much of the interstellar gas and dust was used up by in previous burst of star formation.
5.4 billion years from now - The Sun's core runs out of hydrogen, and it enters its first red giant phase, becoming 1.6 times bigger and 2.2 times brighter than today.
6.5 billion years from now - The Sun becomes a full-fledged red giant, 170 times bigger and 2400 times brighter than today.
6.7 billion years from now - The Sun starts fusing helium and shrinks back down to 10 times bigger and 40 times brighter than today.
6.8 billion years from now - The Sun runs out of helium and, too small to start fusing carbon and oxygen, enters a second red phase. It is 180 times bigger and 3000 times brighter than today.
6.9 billion years from now - The Sun begins to pulsate every 100,000 years, ejecting more and more mass in each pulse, and finally throwing off all but the hot inner core, becoming a white dwarf.
7 billion years from now - the cores of the Andromeda Galaxy and Milky Way merge to form a large elliptical galaxy. The aging population of stars is no longer concentrated along a plane, but instead spread out in an ellipsoid. Star formation diminishes.
1013 years from now - The smallest and longest-lived stars capable of supporting fusion today, red dwarf stars with a mass about 0.08 times that of the Sun, run out of hydrogen.
1014 years from now - All normal star formation processes cease. The universe settles down with a population of stars consisting of about 55% white dwarfs, 45% brown dwarfs and a small number of neutron stars and black holes. Star formation continues at a very slow rate due to collisions between brown and/or white dwarfs.
1017 years from now - All currently existing white dwarf stars cool to black dwarfs with a temperature of at most 5 Kelvin.
1019 years from now - All galaxies "boil off", gradually losing their dead stars to intergalactic space.
1.9 × 1019 years from now - Half of all bismuth decays. All isotopes of bismuth are unstable and the most common, longest-lived one, bismuth-209 has a half-life of 1.9 × 1019 years.
3 × 1022 years from now - All binary brown stars spiral in and collide due to gravitational radiation.
1.8 × 1022 years from now - Half of xenon-124 decays. This is the half-life of this isotope of xenon-124.
1023 years from now - All galactic clusters boil off.
Temperature: 10-13 Kelvin.
From then on: the Universe expands exponentially and cools down to a temperature of 10-30 Kelvin. The longest-lived stable isotope known, tellurium-128, has a half-life of 2.2 × 1024 years. All black holes eventually evaporate, and all other forms of matter eventually disperse into individual elementary particles.
Note: the future sounds pretty boring here, but that's because I've had to omit all the exciting but unpredictable twists due to future discoveries by various forms of intelligent life. We can't really tell what will happen! What you do may have an effect - so be good.
Also try these:
Also try my webpages on mass extinctions and climate change.
For more on the very early history of the universe, click here.
For more on the history of the Earth, click here.
For more on the end of the universe, click here.
An earlier version of this timeline is also available in PDF format.
© 2012 John Baez