I understand that in “Interstellar” Earth was going through some kind of a dust bowl. But considering how bleak every other planet they experienced was, how could it be any worse than a random planet in another galaxy?

I’m not sure if I missed an explanation, but was all of earth infertile? Could not agricultural technology—such has hydroponics—be used?

What specifically made Earth fully “broken” to the point where we’d consider finding a new planet which would need to be so perfectly balanced in chemistry and temperature to Earth’s population to live again?

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    I haven't seen the movie yet, but this is a great general SF question. A good real life question, too. – Joe L. Nov 11 '14 at 3:04
  • I think it's just one of those "too little, too late" problems mankind has faced in the past (much like the dust bowl you mention.) By the time we knew what was happening, the tipping point had already arrived. And all we could do was sit back and wait for the dust to settle. Our planet is a highly complex organism. Even with all our 21st century knowledge and gadgetry, it can be exceedingly difficult to anticipate exactly what effects our actions (or natural phenomena) may have on a global scale. – b1nary.atr0phy Mar 9 '16 at 5:58
  • Related: Condition of Earth in Interstellar – TARS Feb 10 '17 at 1:12

The idea in the movie was that there is a microorganism called the Blight which is affecting the crops, one by one, to the extent that corn was the last crop that hadn't been significantly impacted.

It is indicated in the movie that the Blight breathes Nitrogen, which is registered as significant (it isn't, per se, but for the purposes of the movie, we take that as a given). Given that Nitrogen is 78% of the atmosphere, and Oxygen is only 21%, the movie implies that we cannot win. I think if you have to hang the entire "why we have to go to space", it's on that idea, take it or leave it.

I don't accept the specific reason, the Nitrogen-breathing, but I can imagine a microorganism that significantly affected crops across the board, to the extent that it's not a matter of extinction, but that there's going to be a very sharp rise in the price of food for a long time until the population declines into a much smaller equilibrium, e.g., human population before the advent of agriculture. The Potato Famine, which they mention in the film, is that on a smaller scale.

I think I would have reengineered the script with a line about "since agriculture adopted all of these crops with the common genetic modification that the Blight attacks..." But supply and demand curves (and politics especially) don't make for very good sci-fi.

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    I thought the point of the nitrogen stuff was that once the Blight had killed off the earth’s food crops, it would kill off the earth’s other plant life too, which would halt the production of oxygen required to keep the earth’s atmosphere breathable by humans. It wasn’t stated very specifically in the film, but all the references to suffocation indicate that running out of oxygen is the ultimate problem, not food shortages. – Paul D. Waite Nov 13 '14 at 10:44
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    Yeah, that makes sense, too. They had about three-and-a-half films' worth of exposition they had to cram into a single movie. – Chris B. Behrens Nov 13 '14 at 16:23
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    Indeed, I think they were respectably restrained on that score. – Paul D. Waite Nov 13 '14 at 21:47
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    But what the heck would prevent the blight from coming to the new planet? If they can't isolate it under the ocean or in Antarctica, why should a different planet be any different? – Daniel Williams Mar 31 '15 at 1:16
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    A line about genetic modification would have been a very bad idea. The writers specifically avoided the preachy "stop messing around with nature" message that has become all to common in modern SF, choosing instead to portray nature as simply impersonal. It is not because of anything people did that the crops are dying, it is just that Earth, nature, and evolution don't care about the survival of any particular species. – KSmarts Apr 6 '15 at 19:16

The movie takes this as a premise without much explanation, leaving much room for hypotheses. As Chris pointed out in his excellent answer, it is mentioned that this blight is killing off all the food crops and presumably also other plant life. We may assume that the devastation of plants and more specifically forests is also causing those sand storms. On a deserted land winds can get stronger and more easily lift dust off the ground.

The movie briefly mentions the blight breathing nitrogen and thus posing a danger for oxygen breathers.

While nitrogen is often considered an inert gas, there are biological organisms that convert it into other compounds (nitrogen fixation). Interstellar does not explain how this is dangerous but implies that the blight has some kind of advantage because it consumes a gas that makes up 78 % of our atmosphere, while humans (and other organisms) breathe oxygen (21 %).

It is not plausible for an organism to have a major effect on atmospheric proportions of nitrogen or oxygen on a relatively short time scale but a possible danger could rise from other gases being created out of nitrogen. A more direct and perhaps more likely danger is that when there are no plants consuming carbon dioxide by photosynthesis, the level of atmospheric CO2 rises. Carbon dioxide has a wide range of effects even at its current level of 0.04 % and a major increase would cause suffocation symptoms and eventually death in humans.

Airborne blight microbes are a likely cause for the lung problems that the farmers are suffering of but the specific cause is not mentioned.

The most severe and current problem is the shortage of food, and that has already eradicated most of the population. Possibly parts of Earth have been nuked from the orbit, perhaps in an effort to destroy the blight, or to avoid widespread chaos as people starve to death. This is mentioned as a reason why people would distrust NASA and science.

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In Universe explanation
(as others have pointed out), the main cause in the movie was the Blight. It was killing food crops and all oxygen producing organisms in general.

Other issues mentioned obliquely and can be inferred to have contributed:

  • Climate change (warming and drying)
  • At least one major or multiple smaller regional wars
  • Over population
  • Rampant consumerism

Out of Universe explanation
The movie was about adventure and exploration. Space travel is terribly expensive. The script writers wanted to put forward some possible rational for paying for such a costly endeavor. Survival of the species is a pretty good reason, IMO.

To that end they didn't much care about the details of the Blight (and didn't provide us with any). They just wanted something ultimately deadly to humanity, that wasn't actually killing people at the moment & that provided a reason to drive us off the planet.

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  • Yeah, but it made no sense! I mean, usually “saving the world” movies have the good manners to explain exactly what the world needs saving from. I get that the point of the movie was about wormholes and time travel and stuff, fine. All that—everything after they left Earth—made perfect sense to me. Why do people act like that was the confusing part? I had trouble enjoying the whole second and third acts of the movie, because nothing of what was going on on Earth made any sense. When is this set? Why has some technology advanced greatly, and some not? What the hell is the Blight? Etc. – Josh Zmijewski May 1 '15 at 10:23
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    If you look at most SF movies, often the initial premise is ridiculous. It's only because Interstellar tries so hard in other areas that this one is so obviously silly/underdeveloped. I mean we have microorganisms that metabolize N2 from the atmosphere. They are nitrogen fixing bacteria and are a good thing. But really the movie was long enough that it was OK with me that they didn't spend more time on this point. – Jim2B May 1 '15 at 15:26
  • Ehh, I mean… I dunno. I guess. But not really, though. – Josh Zmijewski May 4 '15 at 15:03

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