Orders of magnitude (time)

Have you ever thought about how long a second really is? Or how short a millisecond is? An order of magnitude of time is a way to organize time into different scales, from incredibly tiny fractions of a second to billions of years. It's like using a zoom lens to look at time, from the blink of an eye to the age of the universe.

We usually measure time in base units like seconds or years. We then add prefixes to show if we're talking about a much smaller or much larger amount of time. For example, "milli-" in "millisecond" means one-thousandth. We don't usually use prefixes for years, so we say "a million years" instead of "a megayear."

The smallest slice of time that scientists can imagine is called the Planck time. The largest amount of time we know of is the age of the universe, which is about 13.8 billion years old. That's the time that has passed since the Big Bang.

Tiny Slices of Time

Let's look at units of time that are shorter than one second. These moments are so fast that we can't experience them, but they are very important in science and technology.

The Smallest Possible Moment

Scientists believe the Planck time is the smallest possible unit of time that makes sense in physics. It is an incredibly tiny fraction of a second, so short that it's almost impossible to imagine. It is the time it takes for light to travel the smallest possible distance.

From Seconds to Centuries

Now let's look at larger amounts of time, starting from one second and going up. These are units we are more familiar with in our daily lives.

Cosmic and Geological Time

To talk about the history of our planet and the universe, scientists need even bigger units of time. These time scales are so long they are hard to comprehend.

• Mega-annum (Ma)

This means one million years. It is often used in geology and paleontology. 2.5 Ma: The approximate time since the earliest human ancestors, like Australopithecus, appeared in Africa. 66 Ma: The time since the Cretaceous-Paleogene extinction event, when the dinosaurs (except for the ancestors of birds) went extinct.

• Giga-annum (Ga)

This means one billion years. It is used for talking about the history of planets and the universe. 1 Ga: The Sun will become so hot in about 1 billion years that life on Earth will no longer be possible. 4.5 Ga: The approximate age of the Earth. 13.8 Ga: The approximate age of the Universe. This is the time since the universe began with the Big Bang.

See also