### Bacteria growing in a bottle

This little exercise gives you a feel for exponential growth and what it means to resource availability. To get the basic idea try this. Given: a bacteria in a bottle of substrate fills the bottle in one hour, starting from one bacteria. The bacteria divides every minute. Calculate: how full is the bottle at 59 … Continue reading

### How much land per person

At present some 11 percent (1.5 billion ha) of the globe’s land surface (13.4 billion ha) is used in crop production (arable land and land under permanent crops). This area represents slightly over a third (36 percent) of the land estimated to be to some degree suitable for crop production. The fact that there remain … Continue reading

### Visualising the green economy

I was thinking the other day as I drove to the shops to pick up screws for a building project that the amount of energy used just to pick up shopping is gigantic. I was wondering how much forest had become fossilized just for me to get that litre of diesel that I used to … Continue reading

### The horse and oat cart challenge

I maintain that this little problem will illustrate how the maximum size of a city is well below that experts currently state. In fact, this problem shows that without fossil fuel the sizes of cities will be severely restricted. This little problem sets a benchmark for how large a city can be, as it is … Continue reading

### How much land do we need to grow vegetables?

GIVEN that the average person needs 400 grams of vegetables a day, and GIVEN that organic market gardens can produce between 350 KG and 1500 KG per hectare CALCULATE the minimum and maximum area of land needed to produce a year’s supply of vegetables per person.

### Open-ended question: how much fertile land is there per person?

How much fertile land is available per person on the Earth. To help you use the units of land measure, remember that one hectare is 100 square meters. If you were standing in the middle of a hectare, 100m by 100 meters, you would have 50 meters to the nearest point on the sides and … Continue reading