Everyday Science
Published in

Everyday Science

A Long, Long Time Ago, In A Really Close Galaxy…

Life began on a small planet orbiting around a small star

Photo by Clément Falize on Unsplash

A matter of generations

My son was born in 2013. I was born in 1978. My dad was born in 1947 and my grandfather in 1912. My father’s grandma — my great grandmother — was born in 1893 (I did not know my great grandfather, he went to America when my great grand mother was pregnant with my grandmother, became a lumberjack in California, fell in love with a nurse, and never came back. OK, this is another story).

110 years and 5 generations passed between my great grandmother’s and my son’s birth. It may seem a long time: in 1893 Italy was still a kingdom and in the USA Grover Cleveland was elected president but, compared to the history of life on Earth is less than a blink of an eye.

Half a billion is a really long time

Woudloper Derivative work: Hardwigg, Public domain, via Wikimedia Commons

Most recent estimations put the formation of Earth around 4.55 billion of years ago (4.55x10⁹ or 4 500 000 000 if you like zeroes). For around half a billion years our planet was a pretty boring place if you were looking for someone because, in fact, life began around 4 billion years ago.

At first sight you might think life appeared pretty soon in history of Earth, but stop a little while: half a billion years is a time longer than that elapsed from the appearing of dinosaurs to today or, put in another way, is 2 000 times longer than the time spent on Earth by humans.

Here come the dinosaurs

I love dinosaurs. They are probably the most incredible creatures ever born; they are big, scary, they have teeth, claws, horns, bony plates…

I long to watch an allosaurus and a T-rex fight for a triceratops corpse, or Deinonychuses hunting triceratopses

But wait.

Dinosaurs reigned for three geological periods — Triassic, Jurassic and Cretaceous — between 237 and 66 million years ago (though technically they are still among us because birds are actually classified as dinosaurs). It means more time has passed from the extinction of allosaur to the appearance of T-rex than from the extinction of T-rex to today. Allosaurs belong, in fact ,to Jurassic and lived between 156 and 144 million years ago, whereas T-rex is a dinosaur from Cretaceous that lived 68–66 million years ago.

Photo by Amy Baugess on Unsplash

And humans?

An asteroid strike, 66 million years ago, wiped out the 75% of the animal and vegetal species, paving the way for the mammals’ dominion and, ultimately, to human race.

Compared to other living beings, humans are like newborns. The first representative our genus homo, homo habilis, appeared in Africa 2.5 millions years ago. Our species, homo sapiens sapiens, has existed for only 200 000 years, less than a moment if you think in geological terms.

Looking at the calendar

Photo by Mockaroon on Unsplash

Imagine having a calendar as long as the life of earth, in which each page is one year. Given the thickness of a sheet of paper is 0.1 millimeters, let’s see how thick this calendar would be.

Let’s start from the first paragraph:

  • my son is almost seven, so the calendar would have 7 sheets: 7x0.1=0.7 millimeters thick.
  • I am 42, so my calendar is 4.2 millimeters thick.
  • the five generations I wrote about spans 110 years, 11 millimeters in the calendar.

We can also look at some historical events:

  • USA declaration of independence belongs to 1776, 244 years ago, so the calendar would be 24.4 millimeters thick, a little less than one inch.
  • Rome wasn’t built in a day but traditionally the foundation date is set in 753 B.C. which is 2773 years ago. The calendar is 277.3 millimeters thick, less than a foot.

Going on with the comparison:

  • the time humans passed on earth is 200 000 years, that in calendar thickness is 20 000 millimeters, 20 meters. Homo habilis appeared 2.5 millions years ago that, in calendar thickness is 250 meters.
  • Dinosaurs ruled Earth from 237 to 66 million years ago, equivalent to a stack of calendar that is 17.1 kilometers thick. If you take the calendar sheet from dinosaur extinction to today you’ll get a pile that is 6.6 kilometers tall.
  • The total thickness of the calendar from the beginning of life to today (4.0 billions years) is 400 kilometers.

So the ratio between the time spent by our species on Earth and the entire life duration on the planet is the same of the height of a six story building compared to the International Space Station orbital altitude.

Something to listen to



Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store
Diego Tonini

Diego Tonini

Writer and science communication enthusiast, I think science can be fun and everyone can understand it!