How Old Is The Earth?

I'm in New Zealand's beautiful Milford Sound, which is actually not a sound but a fjord. So one question you might ask is, what is a fjord? Well, the answer is it's a giant channel carved out of the rock, and it was carved by glaciers—so ice moving down through here at incredibly slow speeds.

How long do you reckon it would take a glacier to carve out a valley like Milford? Millions of years? Yeah, easily. Easily millions.

So I've been going around asking people, how old is the Earth? Wow, that's a good question. I'm not really sure we should know this. Oh, good question. Um, millions of... I'd say probably, I don't know, millions of years old. Maybe four, four, five... millions of years. A couple of million years old? Oh, millions. Millions of years. 2.3 million? No, 3 million. 3.2 million? Do I hear four? Do I hear four million? It's a million, 10 million, 20 million. Nice! I like how you doubled them down. That was good.

I thought it was 36 million, 46 million, 40 billion? Oh, I'd say like three or four months, right? Millions and millions. A billion years old? A couple billion years old? 4 billion, 4.2 billion? Billions years? Yeah, like this.

So the answer is, it's 4.2 billion years old. That's really quite a long time, but I think to most people the difference between a million years and a billion years is, uh, well, it's difficult to imagine.

So let's try to put this in perspective. If you imagine that, uh, my armspan is the history of the Earth, with the starting of the Earth at the tip of my, uh, right fingers, then, well, life would have formed somewhere around my right forearm.

But from there all the way up to, oh, about my left forearm, we only had single-celled, uh, creatures. Then just before my left wrist, we get the first fish, then amphibians, dinosaurs around my, uh, left palm, and finally mammals around the base of my fingers.

Now, dinosaurs lived up until the, uh, second knuckle on my, uh, right middle finger, and humans have only been around for, well, basically the very tip of, uh, my middle finger.

So if you think about the scale of the, uh, the Earth's evolution on that time scale, humans have been here a very short time. In fact, the Earth has been here, uh, for a huge period of time—4.5 billion years.