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Related to D layer: Gutenberg Discontinuity
D layer[′dē ‚lā·ər]
The lower mantle of the earth, between a depth of 600 and 1800 miles (1000 and 2900 kilometers).
The lowest layer of ionized air above the earth, occurring in the D region only in the daytime hemisphere; reflects frequencies below about 50 kilohertz and partially absorbs higher-frequency waves.