The seventy act as emissaries of the Quorum of the Twelve Apostles and First Presidency of the church in organizing, training, proselytizing, and administering to millions of people scattered all across the globe. The seventy are the layer between local church administration and general church administration. In general, seventies must first be at least elders in the Melchizedek priesthood, but in practice most have previously been ordained to the office of high priest. Seventies, being equal in authority, act under the direction of the First Presidency and the Quorum of the Twelve Apostles as they labor in their apostolic ministry. Members of the LDS Church understand that being “equal in authority” (D&C 107:26) means they preside over the church when the First Presidency and the Quorum of the Twelve are not constituted. This means that the seventies have the power to do anything required to organize and administer the church, as long as they do so under the direction of the First Presidency or the Quorum of the Twelve (D&C 107:33–34). They do not, as quorums, preside over the church by their own authority unless the First Presidency and Quorum of the Twelve are no longer in existence. Apart from the seven presidents of the seventy, seventies do not hold priesthood keys but are delegated the necessary keys to perform their duties. Seventies hold apostolic authority in the sense of being “especial witnesses of Christ.” and the Quorums of the Seventy may become the presiding authority over the church if the First Presidency and the Quorum of the Twelve cease to exist. Historically, seven members of the First Quorum of the Seventy were called to serve as the Presidency of the Seventy. This precedent was broken, however, when in 2004 Robert C. Oaks of the Second Quorum of the Seventy was sustained to fill the vacancy created by Dieter F. Uchtdorf's call to the Quorum of the Twelve Apostles. The church now states that the seven presidents are drawn from General Authority Seventies. Historically, members of the Presidency of the Seventy would often serve as heads of various church ecclesiastical departments. This practice changed in 2004, when area presidencies in the United States and Canada were dissolved; these areas were put directly under the jurisdiction of the Presidency of the Seventy. The management of these areas is currently the primary responsibility of the Presidency of the Seventy. In April 2018, church leaders announced that, effective August 1, 2018, three-man presidencies composed of General Authority Seventies would once again oversee areas in the US and Canada.