Let the filing of the gay marriage briefs begin! On Tuesday, proponents of Proposition 8 - the controversial California ballot initiative that defines marriage as between a man and a woman - filed their opening briefs with the Supreme Court, urging the justices to reverse a lower court decision that struck down the state's ban on gay marriage.

Arguments in the case will be heard at the end of March, and briefs from the opponents are due in about a month.

"By adopting Proposition 8," Charles Cooper, a lawyer for ProtectMarriage.com, writes, "the People of California demonstrated their belief that this matter is best resolved by the People themselves, not by their courts. The Equal Protection Clause does not prohibit the People of California - or any State - from making this choice. To the contrary, it leaves them free to do what they are doing - debating this controversial issue and seeking to resolve it in a way that will best serve their families, their children, and, ultimately their society as a whole."

ProtectMarriage.com, the original sponsor of Prop 8, is defending the law because California's elected officials refused to do so. The group argues that preserving traditional marriage furthers society's "existential interests in responsible procreation and childrearing."

"An animating purpose of marriage is to increase the likelihood that children will be born and raised in stable and enduring family units by their own mothers and fathers," Cooper writes." Because relationships between persons of the same sex do not have the capacity to produce children, they do not implicate this interest in responsible procreation and childrearing in the same way."

Cooper criticizes a federal appeals court that struck down Prop 8 on narrow grounds tailored closely to California and its history with gay marriage.

For a few months in 2008, gay couples in California were able to obtain marriage licenses after a ruling from the California Supreme Court. Some 18,000 same sex couples obtained marriage licenses in the state before Prop 8 was passed in November 2008.

In February of 2012, a panel of judges on the 9th Circuit Court of Appeals ruled that Prop 8 "stripped same-sex couples" of the right to use the designation of marriage to describe their relationships and that Prop 8 "serves no purpose, and has no effect, other than to lessen the status and human dignity of gays and lesbians in California and to officially reclassify their relationship and families as inferior to those of opposite-sex couples."

In his brief, Cooper points out that there was only a brief period of time in California's history when same-sex marriage was allowed. He writes, "it is difficult to think of a law with deeper roots in California's and our Nation's history, practices, and traditions than one defining marriage as the union of a man and a woman. That definition has prevailed for all but 142 days of California's 162 year history, and it continues to prevail in federal law and in the overwhelming majority of the States, most often through constitutional provisions much like Proposition 8. "

Cooper makes a veiled reference to the fact that President Obama has only recently come out in support of gay marriage. He writes, "The Ninth Circuit's charge thus impugns the motives of over seven million California voters and countless other Americans who believe that traditional marriage continues to serve society's vital interests, including the citizens and lawmakers of 40 other states, the Members of Congress and President who supported enactment of the federal Defense of Marriage Act, the large majority of state and federal appellate judges who have addressed the issue, an until very recently President Obama. "

Cooper points out that prop 8 left "undisturbed" other laws, including domestic partnership laws available to gays and lesbians in the state.