Its always fun to check the consistency of several quantities quoted in a news article. Case in point:

In a small drop of water there are a billion viruses,” Dr. Wolkowicz said. Virologists have estimated that there are a million trillion trillion viruses in the world’s oceans.

The oceans’ volume is 1.3x10²⁴ cm³. A “million trillion trillion viruses” is 10³⁰ viruses. So the average density of viruses in ocean water is only (1/1.3)x10⁶=7.6x10⁵ viruses/cm³. So if that small drop of water containing a billion viruses is well-mixed ocean water, then its volume must be 10⁹/(7.6x10⁵)=1.3x10³cm³, which is well over a quart. A quart of water is not a small drop.

So what’s the problem? Here’s one way to resolve it. Say the viruses are all concentrated in the top layer of the ocean, the layer having some thickness d. Not an unreasonable assumption, because the viral density no doubt falls with ocean depth. We can estimate d based on the viral density of 10⁹ viruses/drop, and on a reasonable assumption on the size of a drop, say 0.1cm³, giving a viral density of v=10¹⁰cm^-3. The area of the oceans’ surface is a=361x10¹⁶cm². We have

vad=10³⁰ viruses,

so d=10³⁰/(361x10¹⁶x10¹⁰)cm=27.7cm, which is a little less than a foot of depth.

Conclusion: the “million trillion trillion” figure being incomprehensible, one’s sense of scale rests entirely on one’s sense of the volume of the oceans (a lot of drops!) coupled with the billion-per-drop figure. But you see, this is misleading, and by a ratio one may quantify as the average depth of the ocean in feet, which is many thousands.