Baltimore: For example, the AIDS virus could quickly evolve into a far more contagious form, one transmitted by coughing or breathing instead of sex.
Simon: The Earth’s ice caps, melting due to global warming, could release a long-dormant lethal pathogen from before the last ice age.
Leadbetter: Yet another scenario: People could panic about global warming. The warming is largely caused by increasing carbon dioxide in the atmosphere. To save us, they might fertilize the Earth’s oceans to produce algae that will eat much of the atmosphere’s carbon dioxide via photosynthesis. A lot of iron, thrown into the oceans, could do the job. But there might be catastrophic unintended side effects. You might get some new kinds of algae that produce toxins (poison chemicals, not deadly life-forms) that poison the oceans. There would be a massive kill off of fish and plant life. Human civilization depends heavily on the oceans. This could be catastrophic for humans. Is it impossible? Not at all. Experiments have been done where iron was thrown locally into the ocean to produce algae—so much algae that it could be seen from space as green spots (Figure 11.2). Some of the algae that bloomed were of types never before known to science! We were lucky: the new algae were not noxious, but they might have been.
Meyerowitz: Ultraviolet light, streaming through our atmosphere’s ozone hole, could mutate your enormous bloom of algae so it creates new pathogens. These pathogens could wipe out plants in the ocean, and then jump to land and start wiping out crops.
Baltimore: When faced with catastrophes like these, our only hope for dealing with them is advanced science and technology. If, politically, we don’t invest in science and technology, or we hobble them by anti-intellectual ideologies such as denial of evolution, the very source of these catastrophes, we may find ourselves without the solutions we need.
And then there is blight—the consequence of many of these scenarios.
Blight
Blight is a general term for most any disease in a plant that is caused by a pathogen.
Baltimore: If you want something to wipe out humanity, there might be no better way than a blight that attacks plants. We are dependent on plants to eat. Yes, we can eat animals or fish instead, but they ate plants.
Meyerowitz: It might be sufficient for the blight just to kill off the grasses and nothing else. Grasses are the basis of most of our agriculture: rice, corn, barley, sorghum, wheat. And most animals that we eat feed on grasses.
Meyerowitz: We already live in a world where 50 percent of the food grown is destroyed by pathogens, and it’s much higher than that in Africa. Fungi, bacteria, viruses,… they all can be pathogens. The East Coast used to be covered with chestnut trees. They are no more. They were killed by a blight. The species of banana preferred by most people in the eighteenth century was wiped out by a blight. The replacement species, the Cavendish banana, today is being threatened by blight.
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.