ProtoplasmaKid / Wikipedia / CC BY-SA 4.0;

Legion-Media (3);

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Hulton-Deutsch Collection / Corbis via Getty Images;

O. S. Fisher / Shutterstock;

Prolineserver 2010, Wikipedia / Wikimedia Commons / СС-BY-SA-3.0;

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Smithsonian Libraries and Archives / Biodiversity Heritage Library;

Bernd Hildebrandt / Pixabay.com;

Designua / Shutterstock (2);

The National Oceanic and Atmospheric Administration Photo Library;

Keystone / Getty Images;

Chiswick Chap / Wikipedia / CC BY-SA 2.5.