Panthalassa (n.)

"supercontinent of the late Paleozoic era," 1924, from Greek pan- "all" (see pan-) + gaia "earth" (see Gaia). First attested in German, 1920, in Alfred Wegener's "Die Entstehung der Kontinente und Ozeane" (but according to OED the word is not found in 1914 first edition).

word-forming element meaning "all, every, whole, all-inclusive," from Greek pan-, combining form of pas (neuter pan, masculine and neuter genitive pantos) "all," from PIE *pant- "all" (with derivatives found only in Greek and Tocharian).

Commonly used as a prefix in Greek (before a labial pam-; before a guttural pag-), in modern times often with nationality names, the first example of which seems to have been Panslavism (1846). Also panislamic (1881), pan-American (1889), pan-German (1892), pan-African (1900), pan-European (1901), pan-Arabism (1930).

before vowels thalass-, word-forming element meaning "sea, the sea," from Greek thalassa "the sea" (in Homer, when used of a particular sea, "the Mediterranean," as opposed to ōkeanos), a word from the Pre-Greek substrate language. In Attic Greek thalatta, hence sometimes thalatto-.