P1: 介绍实验和发现的一些问题questions and finding of the examining hydrogen isotope
P2:提出一个的问题
解释原因
question: how volatiles arrived?
asteroids and comets
Cuz:jolt --> material flung into the asteroid belt --> arrived at Earth --> bring volatiles
P3: new info. 新发现以及新结论
A. : compared with those in coments
a. frozen water with deuterium
b. research process
c. research result : deuterium lower than in coments
cs. : coments volatiles leaves asteroids
cs.2:CI tallied most colsely with thoes on Earth
Parent bodies were the dominant source of the Eaarth's volatiles