Zank's work, at this point, is mostly theoretical, but he believes the historical record may support his conclusions. Ice cores from the South Pole contain higher levels of a form of beryllium, a rare metal, which is created when cosmic rays strike Earth. Nobody can explain why. He sees one possible explanation. If a cosmic cloud passed by Earth then, it could have weakened Earth's cocoon enough to allow much higher levels of cosmic rays to reach the ground, producing the layers of beryllium.
Guesses range from a greenhouse effect to an ice age.
No one can do anything about it. The people who worry about asteroids think if they have enough warning they can alter the course of an asteroid that would otherwise crash into Earth. But you can't hope to blow away a cloud that may be bigger than our entire solar system. Zank believes cosmic clouds may be just as big a threat as getting hit by an asteroid. Even so, he's not losing any sleep over it.