From a human perspective..

[GoldfishLord]

When Samuel Taylor Coleridge wrote the words, “Water, water everywhere, but not a drop to drink” in The Rime of the Ancient Mariner in 1798, the dangers of drinking seawater had been known for thousands of years. Seawater does indeed make men mad. Historical evidence indicates the ancient Egyptians knew seawater was not potable, but the earliest realization that it was unsafe to drink has been lost to antiquity. (1) In pre-Columbian times the greatest fear of venturing too far from land on the ocean was not falling off the surface of the Earth but lack of fresh drinking water. (2) Saltwater constitutes 97% of Earth’s water, and of the 3% that is fresh, two-thirds is frozen in glaciers and polar ice. Thus, a mere 1% of all the water on the planet (in lakes and rivers, groundwater, and the atmosphere) is fresh and can be used by terrestrial plants and animals.

[From a human perspective the oceans, which cover 70% of Earth’s surface, are still the most extensive and unique desert wildernesses on the planet.]

Source: Water That Makes Men Mad | The Biology of Human Survival: Life and Death in Extreme Environments | Oxford Academic

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I'd like to know the reason why the red part should not be inserted at (1).

 

[emsr2d2]

I'm confused. Where was the excerpt in red placed originally? Was it the beginning of a new paragraph (as you've laid it out) or did it appear directly after "terrestrial plants and animals"?

 

[GoldfishLord]

The answer is (2), but I can't understand why it should not be at (1).

 

[emsr2d2]

It would be odd to put it at (1) because it would break up the sentences that are all about drinking water. Adding it would interrupt the flow.

If you ask a similar type of question again, please leave the relevant text exactly where it appears in the original, mark it out in some way (bold is enough - you don't need to change it to red), then ask about a different position for it.

 

[GoldfishLord]

It seems to me that it would also be odd to put it at (2). It would interrupt the flow.

 

[emsr2d2]

It seems to me that it would also be odd to put it at (2). It would interrupt the flow.

It doesn't. The "drinking water" part is over. The part in bold introduces the fact that the oceans are basically a huge desert and the part after that gives more detailed information.