生成一个包含某个特定主题的电影剧本大纲。
主题：“世界末日”。
Title: The Last Hope

Act I:
- Introduction of main character, John, who is a scientist and has been studying the Earth's environment for years.
- John discovers that there is a massive asteroid heading towards Earth, and it will cause a mass extinction event.
- John tries to warn the government, but they don't listen to him. He then decides to take matters into his own hands and begins working on a plan to save humanity.

Act II:
- John recruits a team of engineers and scientists to help him build a spaceship that can carry a select group of people to a habitable exoplanet.
- The team faces several obstacles while building the spaceship, including lack of resources and time.
- Meanwhile, the government finally realizes the seriousness of the situation and starts preparing its own plan for survival, which involves only the wealthy and powerful.

Act III:
- John and his team complete the spaceship, but they are running out of time as the asteroid gets closer.
- They must now select the people who will be joining them on the spacecraft, and it's a difficult decision.
- The government's plan fails, and chaos ensues on Earth as the world realizes they have no future.
- John and his team launch the spacecraft just in time as the asteroid collides with Earth.

Epilogue:
- The spacecraft arrives at the exoplanet, and John and the others must now start over and try to rebuild civilization.
- They face new challenges on this new world, but they have hope for a brighter future.