Core–mantle boundary Core–mantle boundary The core–mantle boundary (CMB in the parlance of solid earth geophysicists) of the Earth lies between the planet's silicate mantle and its liquid iron-nickel outer core. This boundary is located at approximately 2891 km (1796 mi) depth beneath the Earth's surface. The boundary is observed via the discontinuity in seismic wave velocities at that depth due to the differences between the acoustic impedances of the solid mantle and the molten outer core. P-wave velocities are much slower in the outer core than in the deep mantle while S-waves do not exist at all in the liquid portion of
How the Snake Lost Its Legs a single chapter providing "An evo-devo bestiary," a long list of stories, such as "How the turtle got its shell", "How the vampire bat reinvented running", "How the quetzal got its crest", and "How the firefly got its flashlight". These are "Just So" only in name, since each one is reliably cited to recent research rather than an author's whimsy. Since by this point the reader has been introduced to the core elements of the evo-devo gene toolkit, Held makes each section brief, 50 stories in 32 pages, and minimally technical: he discusses what the evo-devo system achieves in terms