Story highlights. 1  A pregnancy previously was considered term at 37 weeks. 2  Recent research prompted the change.  3 Early term now begins at 37 weeks of pregnancy.
Subduction Zones. Where two tectonic plates converge, if one or both of the plates is oceanic lithosphere, a subduction zone will form. An oceanic plate will sink back into the mantle. Remember, oceanic plates are formed from mantle material at midocean ridges. Young oceanic lithosphere is hot and buoyant (low density) when it forms at a midocean ridge. But as it spreads away from the ridge and cools and contracts (becomse denser) it is able to sink into the hotter underlying mantle.
Convergent plate boundaries. 1  Oceanic-continental The denser oceanic slab slides under the continental slab. The contact region is called a subduction zone, and a trench is formed there. 2  Oceanic-oceanic One of the oceanic plates slides underneath the other. The region of contact is again called a subduction zone.