Assertion: uranium's proportion | /r/HasProperty | constant
Facets:
value: during the period
type: TEMPORAL
Source sentences:
text: Both of these dating methods assume that the proportion of 230Th to 232Th is a constant during the period when the sediment layer was formed, that the sediment did not already contain thorium before contributions from the decay of uranium, and that the thorium cannot migrate within the sediment layer.