In Douglas Adam’s second book of the Hitchhiker’s Guide to the Galaxy series, “The Restaurant at the End of the Universe,” one of the characters, Zaphod Beeblebrox, is to have his mind annihilated by the Total Perspective Vortex — an implement of torture that works by showing you how insignificant you are compared to the vastness of the universe. Zaphod escapes annihilation by being, in fact, the most important person in the universe and eating a bit of fairy cake (cupcake in American English) — you’ll have to read the book.
Indeed, we find it impossible to comprehend the vastness of scale upon which the universe is built. When it comes to size, we are really only comfortable with scales one or two magnitudes on either side of the meter. Anything outside that range is either really, really big or really, really small.
The same is true for time. In Psalms we are told that a good long life is about three score and ten years, but time scales outside our experience are difficult to comprehend.
For instance, grasping the immensity of the 4.55 billion years the Earth has been around is simply beyond our imagination.
The only way to even approach it is to come up with a metaphor that helps us relate time’s vastness to some human scale. I like to think of the Earth as someone who will herself live about 70 years and then estimate how long terrestrial events have taken in Earth’s life. Astrophysics estimate that our sun has a lifetime of about 10 billion years, so if the Earth lasts that long, it has already gone through about half of its life — 31.8 years to be exact. So let’s think of the Earth as a young woman about 32 years of age, no longer a child, but certainly someone with a long life ahead of her.
Now, let’s look at the major events in Earth’s life and when they may have taken place in her metaphorical human years. (We underestimate time periods in our past, so try imagining Earth’s years as your own. What were you doing 8 hours ago, or 2 weeks, or 28 years ago? It will help you see Earth’s time in the perspective of your own life.)
After her fiery birth 4.55 billion years BP (before present), life on Earth may have begun when Earth was only 4 years old (4.0 billion BP), but it took almost 24 more years, when she was 28, (530 million BP) before it became very complex, during the Cambrian explosion. For most of that intervening time, life on Earth was by and large single-celled organisms like algae.
Fishes arose (510 million BP) about 3 ½ years ago.
And it took them almost a year (360 million BP), before they stepped out onto land.
The first dinosaurs appeared around when the Earth turned 30 (230 million BP), but only just died out (65 million BP) about 6 months ago.
Our last common ancestor with apes (6.5 million BP) appeared 16 days and 15 hours ago.
Lucy (3.2 million BP) first stood upright 8 days, 4 hours ago.
Mitochondrial Eve, mankind’s common ancestor (140,000 BP), walked on Earth only 8 hours and 35 minutes ago.
The last ice age ended (10,000 BP) only a little less than an hour ago, but began (110,000 BP) almost 7 hours ago — a snow storm from the Earth’s perspective.
The Great Pyramid (4,560 BP) has only been around for about 16 ½ minutes.
AD or the Common Era has only lasted about 7 ½ minutes.
How long has the U.S. been around in Earth time? About 49 seconds.
But here is the hardest question: In that almost 32 years of age, how long is our own life in Earth time?
You can estimate it this way: Each second of Earth’s time represents about 4.5 human years. So someone living to be 70 would live 15.5 seconds of Earth’s time. If you are 55 years old, then in Earth’s time you have been around as long as it will take to read this paragraph.
Mind-blowing isn’t it? Now enjoy that cupcake.
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