What striking comparison is made regarding humanity's knowledge of Mars versus Earth's oceans?

Answer

Humanity knows more about the surface of Mars than it does about the bottom of our own oceans

Observers note that through dedicated robotic efforts, humanity knows more about the surface of Mars than about the bottom of Earth’s seas, as over 80 percent of Earth’s seas remain unmapped or unseen by humans.

What striking comparison is made regarding humanity's knowledge of Mars versus Earth's oceans?
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