Lithosphere-Asthenosphere boundary found to become deeper under older crust, thus supporting the suggestion that the discontinuity is closely interrelated to the LAB. Beneath oceanic crust, the LAB ranges anywhere from 50 to 140 km in depth except at mid-ocean ridges where the LAB is no deeper than the depth of the new crust being created. Seismic evidence shows that oceanic plates do thicken with age. This would suggest that the Lithosphere-Asthenosphere boundary underneath oceanic lithosphere also deepens with plate age. Data from ocean seismometers indicate a sharp age-dependent LAB beneath the Pacific and Philippine plates and has been interpreted as evidence for
Lithosphere cratons" helps to stabilize these regions. Geophysical studies in the early 21st century posit that large pieces of the lithosphere have been subducted into the mantle as deep as 2900 km to near the core-mantle boundary, while others "float" in the upper mantle, while some stick down into the mantle as far as 400 km but remain "attached" to the continental plate above, similar to the extent of the "tectosphere" proposed by Jordan in 1988. Geoscientists can directly study the nature of the subcontinental mantle by examining mantle xenoliths brought up in kimberlite, lamproite, and other volcanic pipes. The histories