Seismologists Kaiqing Yuan and Barbara Romanowicz have proposed that the magma fueling Iceland's more than 30 active volcano systems emerges from deep within Earth. The great depths involved--nearly 3,000 km--mark Iceland's volcanoes as extreme outliers; ________ many of Earth's volcanoes are fed by shallow pockets of magma found less than 15 km below the surface.

Which choice completes the text with the most logical transition?