Assertion: explosion | /r/HasProperty | underway
Facets:
value: for several million years
type: TEMPORAL
Source sentences:
text: Laid down in the middle-Cambrian, when the "explosion" had already been underway for several million years, this formation contains the first appearance in the fossil record of brachiopods, with clamlike shells, as well as trilobites, mollusks, echinoderms, and many odd animals that probably belong to extinct lineages.