The idea is that around the year 1800 CE the human population became large enough, around a billion people, that its activities started altering the environment.
这种想法出现于公元1800年左右，当时人口变得足够多，大约有10亿人，人类的活动开始能够改变环境。
2
Feeding today's population is a challenge for an already-stressed environment.
养活今天的人口对已经很紧张的环境来说是一个挑战。
3
Finally, the population will reach a size within the carrying capacity of the environment.