tori m. hoehler nasa ames research center. the drake equation: n = r* f p n e f l f i f c l n = the...
TRANSCRIPT
The Drake Equation: N = R* fp ne fl fi fc L
N = The number of communicative civilizations
R* = The rate of formation of suitable stars
fp = The fraction of those stars with planets.
ne = The number of Earth-like worlds per planetary system
fl = The fraction of Earth-like planets where life actually develops
fi = The fraction of life sites where intelligence develops
fc = The fraction of communicative planets (those on which
electromagnetic communications technology develops)
L = The "lifetime" of communicating civilizations
Once the origin of life occurs, how resilient is a biosphere to changes that occur over a planet’s lifetime?
Adaptability
Challenges
Our single example suggests that life can be resilient on time scales of at least 1/3 the age of the solar system
Any of the factors we identified as “extremes” could constitute a challenge to the
long-term stability of life
Harsh conditions for biomolecules(temperature extremes, radiation, pH, unsuitable chemistry)
Resource Limitation(energy, materials, solvent)
A chemically differentiated planetis like a battery . . .
=
(but the battery is only tapped when volcanoes and vents operate)
year
century
million yr.
billion yr.
ten thousand yr.
100 millionmillion10,00010010.01
Hiroshima
Tunguska
K/T
TNT equivalent yield (MT)
Global catastrophe
Tsunami danger
(Credit: D. Morrison)
Terrestrial ImpactFrequency
“Armageddon” Impact(Texas-sized!)
“Catastrophic” depends on who you are and where you live . . .
Temperature (°C)
Dep
th (
km)
2
0
200
1
1000
Geotherm
al Gradient
Surface-Sterilizing Impacts
(Sleep & Zahnle, 1998)
Habitable
Heat-Sterilized
Impact Heating
Energy Balance(Used solar radiation to “charge up” the Earth’s chemical battery (by creating very oxidizing conditions at the Earth’s surface)
Oxygen Production(Toxic for some, great for others – shifted the “balance of power”)
Climate(Consumed CO2 and may have altered the production of other greenhouse gases (e.g., from methanogens, who are sensitive to O2) – this must have affected greenhouse warming and climate)
Radiation Budget(Produce ozone (from O2), which created a shield for UV – less radiation = clement conditions for a greater variety of organisms)
How can life survive (thrive!), in the face of all these potential challenges, on time scales comparable to the lifetime of a solar system?
At an individual level, versatility is important
Tolerance to Extremes
Metabolism
*These factors may sometimes be at odds
Technological Innovation (?)
Sufficient Rates of Evolution
Diversity of Niches, Into Which Organisms Can Evolve
(these have worked on Earth for 3+ billion years)