How does a chicken's egg get its shell?

by | Mar 10, 2009 08:00 PM ET

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Marshall Brain

Hi, I'm Marshall Brain with today's question. How does a chicken's egg get its shell? I mean, does the chicken make the shell and then fill it with an egg white and a yolk? Or does it make the egg white and the yolk and then wrap a shell around it or what? It turns out that the chicken has little to do with the formation of the egg shell. The egg actually grows the shell around itself. It does this using a process that's also seen in bones and seashells. Around the egg, there's a membrane, and on the membrane there are evenly spaced points where columns of calcite form. These columns stack together side by side to form the shell.

The calcium columns grow like crystals, and they fuse together to make a complete shell. The calcite is basically floating in solution around the cell one the membrane's put in place, and it deposits on the membrane to form that crystal. The egg grows its own shell.

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