Amateur Dutch scientist Anton van Leeuwenhoek, who lived in the late 1600s, was obsessed with the minute details of daily life.

Leeuwenhoek studied any living thing he could find in his Delft home, be it the stings of bees, the mouths of fleas, or even his own sperm. He had also pondered kitchen spices, including black peppercorns. He wanted to determine the source of their spice.

After mixing peppercorns in water to soften them, he pulled out his microscope to examine the result. Leeuwenhoek imagined he might spot tiny spikes or arrows on the peppercorn responsible for its zing. Instead, he found tiny spheres with smooth ridges.

But there was something else. Alongside the peppercorns, Leeuwenhoek saw tiny, moving organisms: bacteria—the first ever