3. A minimal volume of 5 ml of a pooled BAL sample is needed for BAL cellular analysis. The optimal volume is 10 to 20 ml. It is acceptable to pool all aliquots of the retrieved BAL ï¬uid for routine analyses (including the ï¬rst retrieved aliquot). 4. BAL cell differential counts with greater than 15% lym-
So when a continent meets a continent, no subduction occurs (instead, the plates collide and thicken). True subduction happens only to oceanic lithosphere. When oceanic lithosphere meets continental lithosphere, the continent always stays on top while the oceanic plate subducts.
Earth is so far the only planet where subduction is known to occur. Subduction is the driving force behind plate tectonics, and without it, plate tectonics could not occur. Subduction zones dive down into the mantle beneath 55,000 kilometers of convergent plate margins (Lallemand, 1999), almost equal to the cumulative 60,000 kilometers of mid-ocean ridges.