( We ( ( decided ( that ( ( the day ) ( was ( ( the time ) ( it ( takes ( Earth ( to ( ( rotate once ) ( on ( its axis ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP We)) (VP (VBD decided) (SBAR (IN that) (S (NP (DT the) (NN day)) (VP (VBD was) (NP (NP (DT the) (NN time)) (SBAR (S (NP (PRP it)) (VP (VBZ takes) (S (NP (NNP Earth)) (VP (TO to) (VP (VB rotate) (ADVP (RB once)) (PP (IN on) (NP (PRP$ its) (NNS axis)))))))))))))) (. .)))
We decided that the day was the time it takes Earth to rotate once on its axis.
(ROOT (S (NP (NNP Earth)) (VP (VBZ rotates) (PP (PP (IN on) (NP (PRP$ its) (NNS axis)) (ADVP (RB once))) (CC times) (PP (IN in) (NP (CD one) (NN day))))) (. .)))