Sentences of a paragraph are given below in jumbled order. Arrange the sentences in the correct order to form a meaningful and coherent paragraph.

A. In Earth’s orbit itself, the U.S. Space Surveillance Network is tracking more than 14,000 pieces of space junk that are larger than 10 cm (4 inches) across, such as defunct satellites and rocket stages.

B. It’s estimated that there are millions of pieces smaller than that. 

C. Humanity hasn’t taken only memories and left only footprints in the outer space but we’ve left a lot of junk up there. 

D. Because of the high speeds at which objects move in Earth’s orbit, even little pieces of space debris can cause damage such as the windows on the space shuttle often had to be replaced because of damage from collisions with debris smaller than a millimeter.