The Science of Interstellar

Kip: I thought that blights are specialists that attack only one narrow group of plants and don’t jump to others.

Leadbetter: There are also generalist blights. There seems to be a tradeoff between being a generalist that attacks many species and a specialist that attacks only a few. For the specialist blight, the lethality can be turned up really high; it can knock out, say, 99 percent of a very specific group of plants. For the generalist, the range of plants attacked is much broader, but its lethality for any one plant in that range might be much smaller. That’s a pattern we see again and again in Nature.

Lynda: Could you have a generalist blight that becomes much more lethal?

Meyerowitz: Something like that has happened before. Early in the Earth’s history, when cyanobacteria started making oxygen, thereby changing radically the composition of the Earth’s atmosphere, they managed to kill most everything else on Earth.

Leadbetter: But the oxygen was a lethal byproduct, a poison, produced by the cyanobacteria; not a generalist pathogen.

Baltimore: We may not have seen it, but I can imagine a very lethal specialist pathogen becoming a lethal generalist. It could spread the range of plants it attacks with the help of an insect that carries it to many species. A Japanese beetle, for example, which eats something like two hundred different plant species, could infect many species with the pathogen it carries, and the pathogen might adapt to attack those species, lethally.

Meyerowitz: I can conceive of a totally lethal generalist: a pathogen that attacks chloroplasts. Chloroplasts are something that all plants have in common. They are crucial to photosynthesis (the process where a plant combines sunlight with carbon dioxide from the air, and water from its roots, to produce carbohydrates that it needs for growth). Without chloroplasts, a plant will die. Now suppose that some new pathogen evolves, for example in the oceans, that attacks chloroplasts. It could wipe out all algae and plant life in the oceans, and jump to the land where it wipes out all land plants. So everything becomes a desert. This is possible; I see nothing to prevent it. But it’s not very plausible. It is unlikely ever to happen, but it could be a basis for Cooper’s world.

These speculations give us a sense of the kinds of nightmare scenarios that could keep a biologist awake at night. In Interstellar, the focus is a lethal generalist blight running rampant over the Earth. But Professor Brand has a secondary worry: humankind’s running out of oxygen to breathe.

12 Gasping for Oxygen

Early in Interstellar Professor Brand says to Cooper: “Earth’s atmosphere is 80 percent nitrogen. We don’t even breathe nitrogen. Blight does. And as it thrives, our air gets less and less oxygen. The last people to starve will be the first to suffocate. And your daughter’s generation will be the last to survive on Earth.”

Is there any basis in science for the Professor’s prediction?

This question lies at the interface of two branches of science: biology and geophysics. So I asked the biologists at our Blight Dinner, particularly Elliot Meyerowitz, and I asked two geophysicists, Caltech professors Gerald Wasserburg (an expert on the origin and history of the Earth, Moon, and solar system) and Yuk Yung (an expert on the physics and chemistry of our Earth’s atmosphere, and the atmospheres of other planets). From them, and from technical articles they pointed me to, I learned the following.

Creating and Destroying Breathable Oxygen

The oxygen we breathe is O₂: a molecule made of two oxygen atoms, bound together by electrons. There is lots of oxygen on Earth in other forms: carbon dioxide, water, minerals in the Earth’s crust, to name a few. But our bodies can’t use that oxygen until some organism liberates it and converts it to O₂.

The atmosphere’s O₂ is destroyed by breathing, burning, and decay. When we breathe in O₂ our bodies combine it with carbon to form carbon dioxide, CO₂, releasing lots of energy that our bodies use. When wood is burned, the flames rapidly combine the atmosphere’s O₂ with the wood’s carbon to form CO₂, which generates the heat that keeps the burning going. When dead plants decay on the forest floor, their carbon is slowly combined with the atmosphere’s O₂ to form CO₂ and heat.

The atmosphere’s O₂ is created primarily by photosynthesis: chloroplasts in plants[24] (Chapter 11) use energy from sunlight to split CO₂ into C and O₂. The O₂ is liberated into the Earth’s atmosphere, while the plants combine the carbon with hydrogen and oxygen from water to form the carbohydrates that they need for growth.

O₂ Destruction and CO₂ Poisoning