  Carbon is an essential element for life but its behavior during Earth's
accretion is not well understood. Carbonaceous grains in meteoritic and
cometary materials suggest that irreversible sublimation, and not condensation,
governs carbon acquisition by terrestrial worlds. Through astronomical
observations and modeling we show that the sublimation front of carbon carriers
in the solar nebula, or the soot line, moved inward quickly so that carbon-rich
ingredients would be available for accretion at 1 au after the first million
years. On the other hand, geological constraints firmly establish a severe
carbon deficit in Earth, requiring the destruction of inherited carbonaceous
organics in the majority of its building blocks. The carbon-poor nature of the
Earth thus implies carbon loss in its precursor material through sublimation
within the first million years.
