The Rare Earth - How Rare is Earth-like Life?


How special are the circumstances that have allowed complex life, like animals and plants, to develop on Earth? In this activity students systematically investigate the time frame for complex life to develop on Earth.

Learner Outcomes

The learner will:

  • discover the relationships between stellar mass, luminosity, and lifetime.
  • set limits on how old, bright or massive a neighboring star can be and still support complex Earth-like life.
  • approximate how many other planets there may be harboring Earth-like complex life in our galaxy.

National Science Education Standards

National Mathematics Education Standards

Materials and Technology

Scientific Background

Teacher Lesson Plans

Activity 1: Discover how old, how bright, and how massive a star should be to support complex life.

Activity 2: Investigate the upper boundary of luminosity for the existence of life.

Activity 3: Estimate the number of stars that can support complex Earth-like life.

Teacher Lesson Plans

Activity 1: How Old, How Bright, and How Massive Should the Star Be to Support Complex Life?

Activity Page One has students interpret a graph that represents stellar lifetime vs. stellar mass on one axis and luminosity vs. stellar mass on the other in order to gain an understandng of the relationship between these three variables. Students will also reason about the minimum amount of time necessary for the development of complex life on a planet.

Activity 2: How Bright is too Bright for Life?

In Activity Page Two, students think critically about the effects of luminosity on the development of complex life. Students will estimate the maximum and minimum luminosity a star must have to support life on an orbiting planet.

Activity 3: How Many Stars is That?

Activity Page Three guides students in an estimate of the total number of main sequence stars that can support complex life.

Lesson Debriefing