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Paul Hoffman and snowball Earth


I was very lucky to attend two seminars given by Paul Hoffman in St Andrews. He is an amazing speaker who manages to convey the excitement of basic science without flashy ways that attract attention for the sake of it. The curiosity of scientists trying to understand the world, is enough, and many times it leads to unexpected discoveries that the scientists would never had predicted. There is even a bit of drama, as some of the discoveries are made after the death of the person that started them.

Paul Hoffman is probably best known for the snowball earth hypothesis, according to which the Earth was completely covered with ice from pole to pole. It is controversial, with most geologists currently being against it. I found the models of planetary dynamics based on ice cover, continent position, sunlight input and CO2 concentration very interesting, especially because they can generate stable equilibria or rapid change.

He also gave a very nice review of the geological literature of the past 200 years. It is possible for a single person to do this because there were not so many publications in the past. I realised the people studying geology during the napoleonic wars were ahead of their time, being concerned with matters beyond their everyday life. It sounds strange for someone in the present to study snail fossils, imagine what people would think 200 years back!

Random lecture notes

The difference between physics and geology is that the only way to understand geology is by understanding its history (the history of the planet). Physics observes the fixed laws of the Universe so the history of the planet is irrelevant. Geology was thus the first self-referential science.

Melting of ice causes global sea level increase, but local sea level decline because of the gravitational pull of the ice at the surrounding ocean. Ice also makes a continent sink, affecting the currently observed sea level mark on a continent.

Fossils became interesting to biologists only when it was realised they represent extinct life. In a world with no evolution, extinction was not necessarily predicted. Biologists did not care about bones when they could have the live organism.

Progress in science happens one funeral at a time as people responding to a new theory rarely change their minds. And the first response to a radical idea is usually negative.

Physicists, who made the first climate models, didn't think a snowball earth could happen because they could not think of a mechanism to melt the accumulated ice, since it reflects heat and we clearly are not in a snowball earth now. Only after the input of geologists did they realise that volcanism could slowly provide the needed CO2 to increase the planet temperature and melt the ice.

During the 3 billion years we have had water on Earth, the Sun has increased in luminosity by 30%. The fact we still have water means that the Earth can buffer its temperature.

An axe and a Toyota are sufficient to do planetary-scale curiosity-driven science of Earth's history. It is a quite good expense to impact ratio.


Here is a video of Paul Hoffman from a previous lecture he gave, it seems similar to what I heard.

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