the stories that have led us to our present condition,

if we want to understand our history,

one of the prerequisites is to have

a good sense of chronometry.

And chronometry, very fancy word,

but it really is just the science of the passage of time.

Chrono relating to time.

Metry, time measurement.

And we take many, many things for granted these days.

We assume that we know what happened the last 50

years, the last 100 years.

And now we're starting to assume we

know what happened 10,000 years ago,

or what happened to our planet 100 million years ago or 1

billion years ago.

But these are all very, very, very new phenomena,

this ability to kind of shine a light on the past.

And even the traditional notions of history,

the traditional stories of, what led to what?

The political nations that formed, the migrations

of people, and then when they happened,

that traditional notion of history

is even fairly new when you think

about just the scope of how long we think humans

have now been on this planet.

And that first traditional notion of history

you can kind of view as the first chronometric revolution.

And that first chronometric revolution

that gives us this kind of traditional notion

of history really just comes out of humanity's ability to write.

So writing gives us our first chronometric revolution.

Because this was the first time, even though we

think humans or human like creatures

have been around for hundreds of thousands

of years at this point, they weren't

able to keep their stories in a very exact way.

They might have had an oral tradition.

It might have gone from one generation to the other.

But with those oral traditions things would get lost.

And the most important information that would get lost

is how long ago did these stories start up?

And we weren't able, as a species,

to really have a firm understanding

of when things happened, and how long ago things happened

until writing became mainstream, and until writing was done

in a way that it became permanent.

And our best sense of when this happened the first time

was by the Sumerians with cuneiform.

And this happened right around the third millennia BC, so

around 5,000 years before the present time.

And this is what some of that earliest writing looked like.

This is actually a letter from, I believe this is from a king.

And you can see it's just highly symbolic carvings.

This is what we more traditionally associate

with cuneiform.

And it was symbolic-based, as opposed to now.

Most of our languages are based on phonetics.

So you have fewer symbols that can represent more meanings.

But this was a huge technological revolution.

I could say, for humanity, because now with the advent

of cuneiform you now had permanent writing that someone

could look at 1,000 years later, 2,000 years later.

And if they can decipher the cuneiform,

they can get a written testimony of what

was happening at that time, and they

didn't have to rely on an oral tradition,

or even guess when that oral story might have started.

But writing, since it only happened about 5,000 years

ago-- so this is 5,000 years before the present,

or you could say 3,000 years BC, give or take.

That was a start.

But this only gave us stories of about 5,000 years old.

And even then it was a very spotty historical record.

We didn't really get really deep history,

depending on where you are in the world,

until really the last few thousand years.

But it was a start.

This was the first chronometric revolution.

But what you may or may not realize is that we are,

frankly, I believe, at the very early stages

of another chronometric revolution that has really

just begun to accelerate in the last 50, 60, 70 years.

And this second chronometric revolution-- I

should write revolution up here too.

This was a revolution.

It allowed us to keep time in a permanent way,

to understand things, to not have to talk to the people

to whom something happened.

We can see their written testimony of it.

But the second revolution really comes out

of the advent of a lot of our understanding

of modern science.

So in the late 1800s you have radioactivity

gets discovered by Marie and Pierre Curie.

So this is 1900 right here.

So this is relatively recent.

Remember, we're talking about a species that has been around

for several hundreds of thousands of years,

and protohumans have been around for millions of years.

And now only 5,000 years ago, at least as far as we know,

was the first writing.

And then only a little over 100 years ago

was the discovery of radioactivity.

And then the ability to use radioactivity.

So radioactivity is interesting.

It's this idea that, essentially elements, can change

from one variation to another of an element over long periods

of time, so through radioactivity.

So they become kind of this natural clock.

No one had to go there and set up a times piece for it.

That luckily, there are these things

that decay at a very predictable rate.

So we discover radioactivity a little over 100 years ago,

and then over the course of the 20th century

we got better and better, more sophisticated

at really understanding radioactivity

to be able to use it to measure the times of things.

And if you fast forward to the second half

of the 20th century, so now say we're at 1950,

this is where the second chronometric revolution really

took hold.

This is where it really took hold,

where we started to understand carbon-14 dating,

we started to understand some of the other techniques

that we talk about as we start to date older and older things.

And I want to be clear.

The radioactivity, the understanding of radioactivity,

was just the beginning of this second chronometric revolution.

The second chronometric, which frankly, we are still

a part of, isn't just radioactivity.

It's also understanding the expansion

of the universe, the constancy, kind of the speed

limit of light that now lets us figure out,

wow, that background radiation we're getting,

that must have been traveling for 13.7 billion years ago.

So we can now look at evidence from our environment.

And our environment is not just the Earth itself.

It's radiation bombarding us from space

that gives us clues as to not just

the age of us, of humanity, the age of species,

the age of the plant, but the age of the universe itself.

So it isn't just about radioactivity.

Radioactivity is a big part of our chronometric revolution.

This is what allowed us for the first time,

if we have layers on the Earth, people have known

for a long time that if we assume

that these layers haven't been jostled,

that something at a lower layer, down here, is probably

going to be older than at an upper layer.

Because year after year you have deposits,

if it hasn't been messed up in some way.

But no one knew.

They said, OK, well, this is relative dating.

This is older.

This is a younger.

But we had no way of knowing that, hey,

is this 1,000 years old?

Or is this 1 million years old?

Or is this 1 billion years old?

But now with radioactivity we could start to say,

hey, we can date some of the rocks here

that are 150 million years old.

And some of the rocks here are about 100 million years old.

So maybe this fossil of a fish that we're finding,

or this primitive fish-like creature right over here, this

would be between 100 and 150 million years old.

And the only way we're able to do this

was with being able to date things using radioactivity.

But radioactivity is just the start.

As I mentioned, we're getting better and better understanding

of cosmology.

We're getting better measurements

of the universe itself.

We're understanding physics at a deeper level.

Now we can start to look at the genome,

and think about how the genome diverges from one species

to another, and how quickly it changes.

So all of these things are just allowing

us to get better and better refinements on the chronology.

Obviously this is a start, but you still

don't know plus or minus 50 million years how old this is

and how this relates to other things that we might find.

So I just wanted to point this out,

that what we take for granted now,

the age of the universe, the age of Earth at 4

and 1/2 billion years old, humans

being around for several hundreds of thousands of years,

this understanding is a very, very, very new phenomenon.

It's due to the second chronometric revolution

that I think we are still a part of.

And even the first chronometric revolution,

this version of history-- and I want to be clear.

History was limited by this first chronometric revolution.

It was limited by whatever was documented.

But now maybe we can expand our notion of history.

And a lot of the videos I've been working on

have been for this big history project, which says, hey,

before history was limited by the first chronometric

revolution, to what was written, by what was testified by people

and was made permanent in some way,

now chronometry has taken us, so that we can understand things

into our deep past, before even the Earth has existed.

So why not redefine history in a big way

for it to encompass everything, for it to be big history.

Anyway, I'll leave you there.

And actually I want to also emphasize

that the second chronometric revolutions is a big deal.

It allows us to transform even our understandings of history.

But even this first chronometric revolution right

over here, 5,000 years is still not

very long in the entire scope of even human civilization.