Medium-Rare Earth

Rare Earth

Right distance from starRight mass of starStable planetary orbitsRight planetary massJupiter-like neighbor Plate tectonicsOcean and continentsLarge moonRight tilt

Rare Earth

Right number/size of giant impactsRight amount of carbon and ironRight atmospheric propertiesRight kind of galaxyRight position in galaxyRight orbit in galaxyRight history (Snowball Earth/ice age episodes)

Path toward complexity

Is there only one evolutionary path to complex animals?

Radiative diffusion

Discussion

Do you think evolution is a completely random process? Explain.

Example: Photosynthesis

In order for photosynthesis to work, you need the right temperature blackbody curve and the right atmosphere.

Evolution

Photosynthesis evolved on Earth to take advantage of the abundant energy supplied by the Sun. We only have one kind because that is the most efficient use of our Sun’s energy.

The Sun didn’t just happen to have the perfect conditions to match photosynthesis

Convergent Evolution

A number of different species evolve independently toward the same solution to optimize survival.

Does Earth have the perfect conditions and history for the formation and development of life, or did life though the process of evolution adapt to perfectly fit Earth’s conditions and history?

The Search for Extraterrestrial

Intelligence

SETI

Tesla – 1901 picked up signals “from Mars” on a large Tesla coil.

Marconi – encouraged everyone to listen to Martian broadcast during the 1924 opposition with Mars.

Low energy radio waves

Long wavelength radio waves get reflected from Earth’s ionosphere

Early detections of extraterrestrial signals likely due to distant lightning strikes

Standard definition TV signal

Discussion

Why are radio signals from natural sources not narrow, but very wide bandwidth?

Drake Equation

N = R* × fplanet × ne × flife × fintell × fciv × L

Discussion

Do you think evolution, given enough time, will always produce intelligence? Explain.

Encephalization Quotient

Plot of brain mass vs. body mass

Discussion

Can you think of any reasons why evolution might favor animals with a lower EQ?

Discussion

What do you think is meant by the expression “evolutionary arms race?”

Drake Equation

N = 1/year × 1 × 1/10 × 1 × 1 × 1 × 100 years

N = 10 civilizations in our galaxy that are currently able to communicate with us.

Distance between civilizations

If N = 10, the average distance between communicating civilizations is about 9000 light years.

Signals from other civilizations

1. Radio/TV broadcasts

2. Interplanetary communications

3. Signal beacons

Interstellar de-coherence

Charged particles in interstellar space tend to spread out or smear coherent radio signals. Interstellar radio messages may not be decipherable.

Discussion

Are you in favor of the government funding SETI? Explain.

Current SETI searches

1. Targeted searches

2. Sky surveys

3. Serendipity

Allen Telescope Array

350 6-meter radio telescopes

WOW signal

Sagittarius

Discussion

Despite repeated attempts a signal from this region of sky has never been detected again. Should we consider this evidence of extraterrestrial life?

Results

After nearly 50 years of searching, no signals from alien civilizations have been detected.

Discussion

SETI proponents argue that absence of proof is not proof of absence and we should continue SETI for thousands or millions of years if necessary. Do you agree, or is there a point at which we should give up?