Bolden appeared Friday before a House of Representatives committee at a hearing on NASA's $18.7 billion budget request for 2012, AAAS ScienceMag.org reported.
NASA has asked for $1.8 billion for Earth science in next year's budget, up 25 percent from current spending levels.
Rep. Frank Wolf, R-Va., asked Bolden if NASA wouldn't be better off letting other agencies -- in particular the National Oceanic and Atmospheric Administration, the U.S. Geological Survey and the National Science Foundation -- take over NASA's Earth science efforts.
Such a move, Wolf suggested, would free up money for NASA to pursue space exploration, and he asked whether there was any overlap in work being done by NOAA and NASA in Earth science.
"Everything we do in Earth science is unique to NASA," Bolden replied, adding that looking down on Earth from space to understand our planet is very much a part of NASA's job.
A 2009 study by the U.S. Government Accountability Office found no duplication of efforts between NASA and NOAA, he said.