It is 1974. Below are five claims that somebody, somewhere, was making at the time.
Some of them turned out to be true. Some turned out to be false. That is not the question.
The question is which of them count as scientific claims.
| Claim | Scientific? Why? |
|---|---|
| 1. Chemicals used in fridges and spray cans will, over the coming decades, destroy the thin layer of gas high above the Earth that blocks most of the sun's harmful radiation. | |
| 2. Everything happens for a reason. | |
| 3. The continents are slowly moving across the surface of the Earth. | |
| 4. Eating carrots improves your night vision. | |
| 5. Your personality is shaped by the position of the planets at the moment you were born. |
✍️ Write here, in one sentence, on your own: what rule did you use to decide? Finish this sentence: A claim is scientific when...
You are about to hear other people's rules.
✍️ Write here: the two or three rules that came up most often in the room. Copy them down exactly as they were said, even the ones you disagree with. We are coming back to them.
Claim 1 is real, and it has a date.
On 28 June 1974, the journal Nature published a three-page paper by Mario Molina, a young researcher who had joined the lab the previous year, and F. Sherwood Rowland, the chemist who ran it, at the University of California, Irvine.
Nature is a scientific journal. Scientists send their work to it, other scientists working in the same field read it and try to find holes in it, and only then is it printed for everyone else. Getting in is difficult. Publishing there does not make a claim true, but it does mean other people have looked at it hard before you do.
To understand what they were claiming, you need two things: what the ozone layer is, and what the chemicals were.
Ozone is a form of oxygen. The oxygen you are breathing is two oxygen atoms joined together. Ozone is three. Most of the ozone on Earth sits in a thin band roughly 15 to 35 kilometres above the ground, in the part of the atmosphere called the stratosphere, well above where airliners fly.