Deep Time

When we humans experience time, we tend to see things in terms of the common units we use to measure time: seconds, minutes, hours, days, weeks, months, and years.

It’s possible for us to think in decades, too, especially once we have a few of those under our belts! Anything beyond decades becomes considerably tougher, though, since nobody we know of has lived for more than 122 years.

Even still, the longer you’ve lived, the more you can personalize the passage of time. You can make sense of a centuries to a degree, considering that a century is about one potential human lifespan, give or take a few decades. There does come a limit, though, as you approach multiple centuries, and this idea of how much time has passed becomes very fuzzy.

Imagining a millennium is difficult enough, but for where we’re going, we need much, much longer time spans. We’re going to need to contemplate time not in the hundreds of years, but in the billions. A billion is ten million times longer than a century, so it’s fair to say that we’ve got some heavy lifting to do here.

This concept is called deep time. The idea is to consider vast stretches of time that are far outside of the normal human experience, so that we can think about how big changes have happened over very, very long times. It’s an incredibly useful skill, and you can get better at it with a little practice.

Let’s start here on Earth. We humans have been around for (very roughly) 300,000 years or so, but this is an absolute drop in the bucket when compared to when most of the dinosaurs were wiped out by a massive asteroid impact. This happened some 66 million years ago, or 220 times longer than we humans have existed, at least in our anatomically modern form.

It’s worth pausing on that for a minute. Everything we’ve ever done, going as far back as the first shelters we built, to figuring out how to communicate using symbols, to learning how to cook with fire, creating tools, migrating out of Africa and eventually to the rest of the world—all of this—falls short of the time when the dinosaurs dominated by more than 200 times.

Can I get a whoa?

Of course, the dinosaurs were sort of the new kids on the block here on Earth, even by the time they were wiped out 66 million years ago. A reign of 165 million years isn’t anything to sneeze at, but it’s still far short of when life first appeared on Earth, at least 3.7 billion years ago.

All that time in between when the dinosaurs disappeared and when we appeared doesn’t seem like such a long time any more. In fact, life showed up on Earth more than 50 times earlier than when the dinosaurs disappeared.

This way of comparing one thing to another is the best way to get a grasp on deep time. Saying the universe is 13.7 billion years old is meaningless without additional context, but if you can describe it as about four times farther back in time than when life began on Earth, you might be getting somewhere.

Astronomers have used standard candles—stars that burn of a precise brightness—in order to calibrate vast distances. Here, we can use our own standard candles of time.

We might not be able to visualize vast amounts of time, but we can certainly visualize their relationships to one another. 4.5 billion years ago, the planet was formed, along with the Sun. In the blink of a geological eye, life appeared on Earth after just several hundred million years.

Earth itself goes back a third of the way to the beginning of the universe. I find that to be somewhat poetic: as unimaginably ancient as our planet is, there are things that are much, much older out there.

By appreciating these immense time scales, we can better understand how long it took us to get here, and how our lives are a mere blink in the eye of deep time. If this makes life seem fleeting, maybe we can draw inspiration from our transitory nature and make the most of life.

Can you can get a sense of our own place in the deep time of the cosmos? Are you able to travel back in time with me today?