and ages to refer to segments of time in the human

or in the pre-human past.

And what I want to clarify right from the get-go--

because frankly, this is something

that's confused me in the past-- is that archaeologists will

refer to eras, periods, and ages in the human past

and they're usually referring to periods of tens of thousands

of years, or thousands of years.

But these are different eras, periods, and ages than the ones

that geologists would refer to when they're

talking about geological time.

In geological time, era means several hundred millions

of years.

Periods and ages mean millions of years.

When an archaeologist, when we're

studying the human past, this is just talking--

they're just generally talking about long segments

of human time, but not in the millions of years,

usually in the thousands or the ten thousands of years.

So what I want to do with that out of the way

is talk about what has happened in the distant human past,

or the distant pre-human past, and also

touch on some of the classifications

for these segments of time-- because they actually tell us

what were the interesting developments that happened

to humanity over the 200,000 years

that Homo sapiens have been on this planet,

or that we believe that Homo sapiens have

been on this planet.

So the longest period of time in human past,

or the category of human time-- and there

are different ways you can categorize

it-- is the Paleolithic Era right over here.

And what really makes that period of time--

so this begins even in prehistory or pre-human

history, so before Homo sapiens even

existed-- you have the beginning of the Paleolithic Era

that really began with the development of stone tools.

And as we learned in the video on human evolution,

there were pre Homo sapiens species

that were using stone tools.

And so the Paleolithic Era, it's really

kind of signified by one, the stone tools, but even more--

that either the pre-humans-- or once

you go about 200,000 years ago-- the humans show up.

It's kind of distinguished by humans

being hunter-gatherers, which essentially means to survive,

we used to walk around a lot.

If we couldn't see something obvious to hunt, maybe

a woolly mammoth or something, if we didn't see something

obvious to hunt, we would look around

for snails, or mushrooms, or whatever else.

And that's how we would survive.

That's how we would live.

And because we were constantly adapting to our environment

based on the seasons, we were maybe following animals

as they migrated, hunter-gatherers

were fundamentally nomadic, which means that they never

settled in one place for a long time.

They were always ready to pick up-- probably their tents--

and follow the herd, or follow whatever animals they were

hunting, or follow the season, so they

could go to warmer climates, maybe,

where they're more likely to find something on the ground

to eat, maybe, during the winter.

Or who knows.

So the Paleolithic Era is really distinguished by that.

It's a huge swath of time in human history.

And it doesn't come to an end until you

get to the advent of farming.

So the Paleolithic Era, I mean, we're literally

talking about over two million years ago

was when it starts-- before Homo sapiens even

existed as a species.

And it goes all the way to the advent of farming,

that we believe first came about around 11,000

to 7,000 years ago.

And this abbreviation right here, this BP,

this does not stand for British Petroleum.

It stands for Before Present, or before the present time.

So one more acronym to have in your tool

kit when you see things.

And obviously, if we're 11,000 years before the present,

that's the same thing as 9,000 years Before Christ,

or Before the Common Era.

Because Christ was, we believe, born 2,000 years ago.

Now, it may or may not be obvious to you,

but the advent of agriculture is a super big deal, arguably

the biggest deal in the development

of human civilization, or in all of human history.

And you might say, hey, you know,

what's the big deal about agriculture?

These characters over here look pretty happy.

They're able to walk around a lot.

They're able to hunt.

What's the big deal of all of a sudden people

plowing fields, and domesticating cattle,

and having chickens to lay eggs, and whatever else?

And the big deal about that-- besides the fact that it would

change people's diet-- is that for the first time,

it allowed them to not be nomadic.

It allowed them to-- and you could have probably

had some hunters who were somewhat settled, maybe living

near the ocean.

Maybe they did some fishing, and all the rest.

But for the most part, with the development of agriculture,

it forced people to stay in one place.

So you have the Paleolithic Era all the way to the advent

of agriculture, which was about 11,000 to 7,000 years ago.

And besides the fact that it changed people's diet,

it allowed them to settle.

So agriculture allowed human beings

to settle down in one area.

And it wasn't just that they were settling in one area,

but because they were able to control their environment, they

were able to increase the density of things,

of crops that humans could consume,

and animals that humans could consume-- and lower

the density of crops that humans can't consume,

and animals that they can't consume,

or that they don't want around, like pests of some type.

What it allowed them to do is also

settle in more dense environments.

You can imagine when you just have people walking around,

you need a lot of land to support

even the calorie requirements of one human being.

But all of a sudden, if you are able to develop agriculture,

you're able to domesticate animals.

All of a sudden you could have-- in the same amount of land,

you could have more calories being generated.

And because you have more calories being generated

in a smaller amount of land, people can settle.

And they can settle in a denser environment.

And so agriculture was really this necessary requirement

for people to develop civilization,

or to develop villages and cities.

And maybe also giving them the free time

to start thinking about hey, maybe we

want to think about how we can record what we know,

how we can develop even more technologies.

And so just to give us a sense of the categorization

that an archaeologist would use for these different periods

of time-- I told you we start with the Paleolithic

Era, with the advent of stone tools,

pre-humans-- most of human time on this planet.

And then about 11,000 years ago, the development of agriculture.

And it developed independently at different places

around the world, which is by itself

an interesting phenomenon.

And people think that it might just be that be the climate

might have warmed up a little bit,

so that people-- maybe naturally there

were some human edible crops that

existed in a little bit of a denser environment,

and humans learned to optimize that slowly,

and they did that independently.

But it's an interesting question of why

did it develop just then after 180,000, 190,000 years,

why did agriculture all of a sudden happen?

But just to get the terminology--

the Paleolithic Era is that period before agriculture.

And then once agriculture starts developing,

we are now in the Neolithic Era.

And some archaeologists will describe a transition period

between the Paleolithic and the Neolithic Era

called the Mesolithic.

And just so you know what these words mean-- because they

actually make sense when you know what they mean,

paleo means old and lithic means stone, or of stone.

So they're really talking about the Old Stone Age.

Neolithic, as you