Summary: Extraterrestrial Life: Problem Set #2
Due, in class, Thursday February14th
1) Discuss the evidence that suggests that the water on the Earth originated
from impacts with bodies originally situated in the outer asteroid belt.
Why are comets not though to have dominated the delivery of the Earth's
2) Some stars' luminosity varies markedly due to periodic stellar pulsations.
Suppose (hypothetically, since this does not happen for stars like the Sun)
that the Sun's luminosity oscillated by 50% on a timescale of (a) 1 hour or
(b) 1000 years. How do you think these oscillations would affect the
habitability of the Earth?
3) Describe how feedback processes operating over long time periods
maintain the stability of the Earth's climate.
4) Describe, in non-mathematical terms, how we can determine the age of
rocks. Be careful to explain what is meant by `age' in this sense.
5) Imagine an extrasolar planet whose surface is 75% covered by ocean and
25% covered by land. If the ocean has an albedo of A = 0.1 and the land an
albedo of A = 0.5, what is the average albedo of the planet? If all the land
is in the form of a single continent close to the equator on one hemisphere
of the planet, sketch how the brightness of the planet (seen by a distant