Peter D. Ward

Professor: Biology, Earth & Space Sciences, U. Washington
Author: Rare Earth: Why Complex Life is Uncommon in the Universe
(w/D. Brownlee, 2003, Springer)
Author: The Life and Death of Planet Earth
(2003, Times Books)

How will humanity first discover ET Life?
Best Guess: biosignatures (Solar System)
Microbial Life
- May be right next door, on Mars, or further out in the ice moons of Sol's children
- Likely first found: under the surface of Mars
Complex Life
- Likely never found (including technosignatures)
- Big problem of current life and planet hunters: Calling so many exoplanets "Earth-Like"
- Bigger Problem: Are tidally locked planets "habitable" for complex life?

The Rare Earth Hypothesis
A
- Planetary systems may frequently have microbial life
- Robust organisms - modest environmental requirements
- Easy to form - hard to extinct
- Microbes were on Earth soon after late heavy bombardment
B
- Animal-like organisms are likely to be rare
- Need special environments
- Hard to form - easy to extinct
- Took ~4 billion years to evolve on Earth