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c. 50,000 BCE -

The ancestors of Australia's Aboriginal peoples (known as ancestor beings) are believed to have lived in a timeless era, known as the Dreamtime.

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c. 8,000 BCE -

A row of 12 pits, unearthed in Warren Field, Scotland, is believed to have worked as a lunar calendar.

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1250 BCE -

A flat sandstone with engraved markings was discovered in Egypt’s Valley of the Kings in 2013. It's believed to have been used as a sundial.

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600 BCE -

Chronos was the god, and the personification, of time in ancient civilizations such as Greece and Rome.

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500 BCE -

Hinduism and Buddhism did not view time as linear. Instead, they viewed it as cycles, where nothing is permanent.

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350 BCE -

Greek philosopher Aristotle defined time as “the calculable measure of motion with respect to before and afterness.”

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100 BCE -

The Maya peoples developed a calendar that tracked the seasons, the phases of the moon, and the times when the planet Venus would be visible in the sky.

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1090 -

A man in China named Su Sung built one of the first mechanical clocks, which is also known as the 'Heavenly Clockwork.' This was approximately two centuries before mechanical clocks began appearing in Europe.

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1582 -

In 1582, Pope Gregory XIII implemented what is now the most used calendar in the greater part of the world: the Gregorian calendar.

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1650s -

It's thought that Galileo Galilei might have been the first person to suggest a pendulum for a clock, though the designs by astronomer Christiaan Huygens were the ones used by Dutch craftsmen to build the first pendulum clocks.

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1687 -

Isaac Newton argued that "absolute, true, and mathematical time, in and of itself and of its own nature, flows uniformly,” so clocks might not be that accurate!

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1729 -

In this year, astronomer Jean-Jacques d’Ortous de Mairan made an important discovery with regards to the circadian cycles. He placed mimosa plants in a darkened room for a number of days and observed that their behavior continued “as if the plants could feel the sun.”

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1824 -

French scientist Sadi Carnot came up with the second rule of thermodynamics, where the concept of entropy somewhat proves the linearity of time. Roughly, the flow of energy can only happen in one direction.

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1884 -

The International Meridian Conference in Washington established that the world would be divided into time zones.

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1895 -

British writer H.G. Wells published 'The Time Machine' in 1895. The time-traveling story makes reference to time as a fourth dimension, independent from other dimensions in space. This was before Einstein’s theory of relativity.

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1905 -

Speaking of which, his theory posits that measure of time is relative to the observer. The exception being what he defined as the speed limit of the universe: the speed of light.

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1907 -

Two years later, German mathematician Hermann Minkowski claimed that intervals in space-time are absolute, despite space and time being relative.

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1915 -

Einstein’s theory of relativity was so crucial for us to understand time that it actually predicted the existence of black holes and gravitational waves.

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1916 -

Not long after, German physicist Karl Schwarzschild did come up with the equations for general relativity and solved a very important one that identified what we now know as black holes.

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1928 -

Time seems to flow in one direction. British physicist Arthur Eddington came up with what he called "the arrow of time." He said, “If as we follow the arrow we find more and more of the random element in the state of the world, then the arrow is pointing towards the future; if the random element decreases the arrow points towards the past. That is the only distinction known to physics.”

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1929 -

Milton Humason and Edwin Hubble discovered that the farther a galaxy is from our planet, the faster it is speeding away from it. This was the beginning of what we know as the Big Bang model of cosmology.

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1954 -

German zoologist Gustav Kramer argued that birds and bees use the sun for navigation. Klaus Hoffmann showed that these 24-hour rhythms do actually assist birds in their navigating.

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1964 -

Arno Penzias and Robert Wilson discovered a glow in the sky using a radio antenna that became known as the “cosmic microwave background,” also described as the echo of the Big Bang.

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1967 -

Before atomic clocks, a second was defined as 1/86,400 of a day. But Earth is not regular as previously thought. It turns out atoms are better at keeping time than tracking Earth’s rotation.

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1972 -

In 1972, scientists discovered the brain region responsible for the circadian rhythms. The suprachiasmatic nucleus, or SCN, processes information from the retina (light and darkness).

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1988 -

In 1988, British physicist Stephen Hawking published 'A Brief History of Time,' where he identified three “arrows of time:” a psychological one, a thermodynamic one, and a cosmological one.

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1989 -

As part of an experiment, a woman named Stefania Follini spent 130 days in a cave in New Mexico. Her sleep-wake cycle increased from 24 to 36 hours. In the end, she estimated that she was in the cave for about 60 days.

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2015 -

The strontium lattice clock is so accurate that it is estimated that if it was around during the Big Bang it wouldn't have gained or lost more than one second.

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2018 -

Norwegian scientists discovered a number of cells in the brain that appear to play a role in awareness of time’s passage linked to memory formation.

Sources: (Quanta Magazine)

See also: The best science podcasts for curious minds

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