about how humans, over time, have gotten better and better

at getting more calories out of a given unit of land. And one thing I do

want to emphasize, in the last video, these

numbers that I came up with– I picked these numbers

to make the math fairly simple– and to give you

the general idea. I don’t want you to

think that the most that a square kilometer

can support today is exactly 1,000 people. It depends, hugely, on

what the land is like. How much of the land you’re

actually using for agriculture. What crops you’re

planting, et cetera. How the people are living. How many calories they need. The whole point

of the last video was just to give you a

framework that, wow, there is this upper bound based on how

much productivity you actually get from the land. Now, what we want to think

about in this video– that was– the last video was

this axis right here, getting more and

more out of the land. What I want to think about in

this video is, how did humans, through different

technologies, how did we get by doing less

and less of the labor for getting those

calories out of the land? Obviously, you just don’t have

land and thing spontaneously grow– well, I guess that

would happen in the wild. But if you’re doing

agriculture, you need to put some

energy into the land. You’ve got to work the land. And so what we have

over here in this chart, and this chart is

derived from information from this book right over here. This is Energy and Society. And what we want

to think about here is the different

ways that humans have gone about to till soil. So we’re not even going to

think about the total process or the total energy required

to grow a certain crop. What we’re just going

to focus is one step of the agricultural process. And that is tilling the soil. And in case you’re like

me and you have never worked on a farm– which,

that’s one thing I would like to change one day is actually

go through that process– but tilling the soil is

kind of churning it up. So you get the nutrients

from the bottom layers to the surface. You bury all of the remains

from the last harvest. You bury all of the

weeds so that they die. And you also get

air in the soil. What it does is it

essentially prepares the soil for the next

agricultural cycle. So it’s a process

that humans have been doing since antiquity. And what I want to

do, in this video, is think about the

different ways to do it. And how much energy

is required to do it. And we’re going to think

about the energy in two ways. How much of that energy

comes from humans? And how much of

that energy comes from things other than humans? So just as an example, when

we talk about human power, we’re talking about

someone literally hand-plowing this field. So this woman right

over here is literally– she has this little cart that’s

digging up the soil behind her. When we talk about

oxen power, we’re talking about the oxen

doing most of the work. They’re the ones dragging

this plough which is digging up all of the soil. And this gentleman has

to be there to supervise. But this still is

fairly intense labor that this gentleman is

doing right over here. And then, when we

talk about tractors, we’re talking about

a scenario like this. Where the tractor is doing most

of the work of actually digging up, dragging this

plow behind it, and digging up all of the soil. And from this book

right over here, that’s where we

got these numbers. I’ll tell you which

numbers I got from them and which numbers I reasoned

through, because I wasn’t fully comfortable with the

numbers that they had. But these are their numbers. That, if you are human power,

to till one hectare of soil, it’ll take 400 hours. Oxen power– and this

should be a pair not a pari. That should be a pair

of oxen, 65 hours. A 6-horsepower

tractor, 25 hours. A 50-horsepower

tractor, four hours. And in case you

all are wondering, what is a hectare of soil, it

is literally a plot of land. A hectare of soil. Let me write it. A hectare of land

is a plot of land that is 100 meters

by 100 meters. And it’s roughly equal to 2 1/2

acres, not exactly 2 1/2 acres. It’s like 2.4. I think 2.47 something,

but roughly 2 1/2 acres. So we’re just thinking about

how many hours to essentially dig up all the soil for plot

of land 100 by 100 meters. So what we have over

here, so clearly, human takes a lot longer. Oxen, they can do a

little bit faster. 6-horsepower

tractor, even faster. A 50-horsepower tractor,

very powerful tractor, even faster than that. Now, this column right

over here is the amount of energy required to

actually produce and maintain the machinery used. So this is a very

unintuitive thing. Whenever you think about–

for example, whenever you think about the

amount of energy to plow this land over

here, you tend to think, OK. Well, this individual

is going to have to expend a lot of her energy. You don’t think about the

amount of energy required to actually maintain the tool. To one, build the tool that

she’s using, in this case, a hand plow. And then, to maintain

that as she does it. And so this estimate– and I

got these two from these fellows right over here, or, actually,

one of them might be a gal. But it’s about

6,000 kilocalories. And this is k. This is kilocalories

for lowercase c. And one thing I want

to emphasize here, one kcal is equal to, is the

same thing as one calorie with a capital C, which

is the same thing as 1,000 calories with a lowercase c. And we talked about

this in the last video. But when people talk

about food calories, they’re really talking about

a calorie with a capital C. Or you could say they’re

talking about kilocalories. So your candy bar,

200 calories, they’re talking about this

right over here. In chemistry class, when you

talk about the amount of energy to raise a gram of water

one degree Celsius, you’re talking about

these calories here. So in all of these numbers in

this chart right over here, they are in either–

you can either view as this unit, kcals,

kilocalories, or calories with a capital C.

They’re essentially the same units that we

used in the last video. And these are the

same numbers that you are used to from a dietary

calorie point of view. So for example, 6,000

calories, that’s about how much of a typical

male would expend in three days. So this is to maintain it over

the course of these 400 hours, in the case of the hand plow. And the total amount

of calories that were needed to make

the plow divided by the total number of hours. So whatever fraction of the

plow’s life is being used here, you use that fraction

right over here to put this 6,000 calories. But needless to say,

for at least the plow, for either the human

or the oxen scenario, this isn’t a significant

amount of the total calories. So obviously, if

you’re doing it either with human or oxen power,

you’re not using any gasoline. You’re not using any petroleum. In all of these

scenarios, we’re going to assume that someone has

10 working hours in the day. And that right over

here, this is a measure of how hard that

person’s work is. And I estimated

these numbers here. They’re slightly different than

what the original numbers were in this book right over here. But we’re saying, look. If you are actually walking

along using this hand plow, that is actually very,

very vigorous activity. So it is going to require

about 400 calories per hour to do this type of activity. You do it over 10 hours. It’s going to require

4,000 calories just to do that over 10 hours. And then, we’re assuming

that there’s some rest. That the rest of the day,

you’re going to walk around. And maybe you’re going to

cook dinner, eat breakfast. You’re going to

sleep some of it. We’re assuming that the

other 14 hours a day are going to be at about

100 calories per hour. And so this is the total. If someone were to,

using this technique, work for a total

of 10 hours, this is how many calories they

would consume in the day. And you can see, this is

the most labor-intensive. So it looks like that

they would consume the most calories per day. These two are the

least labor-intensive. You’re sitting on a

tractor although that still requires more calories than

sleeping or watching TV, and so that’s the number of

calories they would consume. Now, this right

over here– and this is the interesting

number, or one of the really interesting

numbers– based on all of these

assumptions, this is the total human

input in calories to do this task, to till

this one hectare of soil. So over here, you’re using

5,400 calories a day. If you’re working

10 hours per day and it requires 400

total hours, you’re going to be working 40

days, 400 divided by 10. 40 days times 5,400

calories per day. It’s going to take a human–

just the human part, not even thinking about

the 6,000 calories necessary to maintain and

make that plow– the human is going to spend to

216,000 calories to till, to plow that one

hectare of land. And if you add the other

6,000 in for the actual plow– and you could debate what

this number should be, but it’s not a significant

number compared to this– you get about 222,000

total calories. When you go to the

oxen situation, you’re requiring fewer hours. And each hour, it requires

a little less calories. This is still labor-intensive,

but not as labor-intensive as what this woman right

over here is doing. So on a daily basis, using

a little bit fewer calories. But since you’re only

doing 6 1/2 days of this, 65 hours divided by 10,

you’ve significantly reduced the number of calories, the

total number of calories that the human needs to

put into this task. Now, there still is

other energy being done. And now all of a sudden, the

oxen have gotten involved. And if you assume that each oxen

consumes about 20,000 calories a day, and you have two of them. So 40,000 calories per

day just to feed the oxen. And you’re going to do that for

6 1/2 days, 65 divided by 10, the oxen are going to consume

260,000 calories to do this task. So the total energy input

here, now, has gone up. So this is an

interesting phenomenon that is going on

right over here. What the human is

putting in, as we get better and

better technology, goes down substantially. 216,000 to 33,000, and

we’ll see with the tractor goes down even more. But the total energy, if you

include the amount of energy that the oxen have to

put in, or if you include the amount of energy

due to the gasoline that has to be used for the tractor,

the total amount of energy is going up to plow that field. But the human energy

goes down dramatically. Now, the last thing I

want to highlight here– and these are where my numbers

depart a little bit, or fairly significantly, from this

original study right over here, this original estimate–

is the machinery input on the tractors. So if you look this up, and

you could Google search it, they have much

larger numbers here. But I did a little research. And it looks like, for

most petroleum-based, combustion-based engines

or vehicles, roughly 20% of the total energy that’s used

in fuel, 20% of that energy is used to for the actual

production and maintenance of that vehicle over its life. So what we did over

here is, we said, OK. For a 6-horsepower tractor–

I used their numbers– where you’re going to have

to use 25 hours to do it, it’s going to use

this much petroleum, assuming that it uses 23.5

liters of gas or petroleum over 25 hours. And then, I just took

20% of that number for saying, well,

how much energy had to be used to

maintain that vehicle over that amount of time? And if you think about what

fraction of this vehicle’s life that 25 hours

represents, that fraction times the total amount of

energy required to produce that. So remember, these

things are made of metal. They had to be made in furnaces. So just producing a vehicle

requires a lot of energy. And so this right

over here is 20%. And I just use

that rule of thumb for most petroleum-based or

combustion-based vehicles. That 20% of the total

energy expenditure over the course of

that vehicle’s life is roughly equal to

the amount of energy used to produce that vehicle. But either way, you go

all the way over here. The human has to spend

less calories sitting on the vehicle. So they spend less

calories per day. And then, the total human

input right over here, for the 6-horsepower tractor,

it’s going to take them 2 1/2 days– 25 hours at

10 hours a day– is going to be 8,500 calories. But of course, you

have the petroleum used and then some estimate

of the amount of energy used to produce that tractor. And you’re just taking the

fraction over that 25 hours. You’re not taking

the entire life of that 6-horsepower tractor. To produce a

6-horsepower tractor, this number would be

much, much larger, if you talked about the

total number of energy. We’re just taking the

small fraction of its life that we’re using

it right over here. Same thing for the

50-horsepower tractor. But any way you look at

it, the human– and this is a really interesting thing. Humans, by going

from human power all the way to a

50-horsepower tractor, you’re getting almost a

factor of 200 improvement, in terms of how

little energy has to be put in by the

human to till that land. But you actually get

a total increase, if you factor in things like the

petroleum and then, definitely, the amount of energy to

actually produce that machine. So anyway, hopefully, you

found that interesting. I find this– it’s

something that you don’t think a lot about. How much energy input

has to be put in? And oftentimes, we only think

about the human energy input. But we’re not thinking about the

energy input from other things, like oxen.

© Copyright 2019. Tehai. All rights reserved. .