We’re celebrating 20 years of Earth Science Picture of the Day during the month of September! Today’s photo features a popular EPOD from the past. Thanks to all of our followers (on the blog, Facebook, Instagram and Twitter) for supporting us. Thanks also to all of you who’ve submitted your photos. We’re most appreciative. This EPOD was originally published December 24, 2018.

Photographer: Southern Maine Community College Photography Class

Summary Author: John Stetson

This wreath is certainly festive and seasonal, but it's just a bit too small, about the width of a human hair, to place on the front door to welcome guests. It's made from a common species of diatom (Eucampia zodiacus). Why can diatoms look so much like stained glass windows in a Cathedral? They're made from opaline silica, SiO2 -- the material of opals and glass.

Diatoms are critically important in that they're the beginning of the food chain. Aquatic plants (of which diatoms are the most prolific) supply 50 percent of the oxygen on Earth, and when they die they sink to the bottom of the oceans, acting as a carbon sink. Photo taken on December 2, 2018.

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