Assertion: solar energy | /r/ObjectUse | used by human
Facets:
value: as early as 7th century
type: TEMPORAL
value: in theory
type: OTHER
Source sentences:
text: How is solar energy used by humans?
text: In theory, solar energy was used by humans as early as 7th century B.C. when history tells us that humans used sunlight to light fires with magnifying glass materials.