( ( ( ( ( ( ( ( About 4,000 ) species ) ( of prokaryotes ) ) ( have ( been described ) ) ) , ) but ) ( there ( are ( ( an ( estimated ( ( ( ( 1 to ) 3 ) million ) ( undescribed species ) ) ) ) ( ( living ( on Earth ) ) today ) ) ) ) ) . )
(ROOT (S (S (NP (NP (QP (RB About) (CD 4,000)) (NNS species)) (PP (IN of) (NP (NNS prokaryotes)))) (VP (VBP have) (VP (VBN been) (VP (VBN described))))) (, ,) (CC but) (S (NP (EX there)) (VP (VBP are) (NP (NP (DT an) (VBN estimated) (QP (CD 1) (TO to) (CD 3) (CD million)) (JJ undescribed) (NN species)) (VP (VBG living) (PP (IN on) (NP (NNP Earth))) (NP (NN today)))))) (. .)))
About 4,000 species of prokaryotes have been described, but there are an estimated 1 to 3 million undescribed species living on Earth today.
(ROOT (S (NP (NNS Prokaryotes)) (VP (VBD were) (NP (NP (DT the) (JJ first) (NN living) (NNS things)) (SBAR (S (VP (TO to) (VP (VB evolve) (PP (IN on) (NP (NN earth))))))))) (. .)))