It has inspired countless chin-scratching conversations, but researchers in the U.K. says they have finally answered the classic unanswerable question about chickens and eggs:

So why did the chicken come before the egg?
Scientists from Sheffield and Warwick in the U.K. have found that egg shells can only be formed by a particular protein found in a chicken's ovaries. Ergo, an egg can only exist if it has emerged from a chicken. 

What is an eggshell made of, exactly?
Calcite crystals, mainly. The magic protein — named ovocledidin-17, or OC-17 — allows the chicken to convert calcium carbonate into calcite crystals and produce eggshell. Chickens are able to create 0.2 oz of shell every day. "The protein had been identified before and it was linked to egg formation," said Dr. Colin Freeman of Sheffield University's engineering department. "But by examining it closely we have been able to see how it controls the process."

So is the debate over, then?
Not exactly. "Eggsperts" have solved this problem before, but with the egg coming first. Evolutionary geneticists reported back in 2006 that, because genetic material does not change during an animal's life, the first organism that we know as a chicken would have to have been produced inside an egg. "The first living thing which we could say unequivocally was a member of the species would be this first egg," Professor John Brookfield said.   

What do the creationists say?
Chickens came first, according to John D. Morris of the Institute for Creation Research. On the fifth day of Creation, God created "every winged fowl after [their] kind," then blessed them saying "be fruitful and multiply" (Genesis 1:21-22). "For the chickens, this meant lay chicken eggs. Problem solved."

OK, so if a tree falls in the forest...
Actually, one researcher claims to have solved that one, too: It makes a sound. Perhaps it's time scientists tackle the other great "chicken-centric mystery of the universe," says Juli Weiner at Vanity Fair, "namely, its motivations for crossing the road."

Sources: Daily Mail, CNN, Institute for Creation Research, Vanity Fair