HW 9 - due 25 April
R+D: 28-1, 28-2, 28-7, 28-12, 28-13, 28-15, 28-18
Problems: 28-1, 28-8
Life in the Universe
Cosmic Evolution
Cosmic evolution: the continuous transformation of matter and energy that has led to the appearance of life and civilization on Earth
Seven major phases: particulate, galactic, stellar, planetary, chemical, biological, and cultural
Previously we have been studying the first 4 phases
Is this progression of phases natural, or is it random- implying that life on Earth is unique
Arrow of Time
Fig. 28.1
Life
What is life?-Seemingly simple question, very hard to answer
Definition of Life: Characteristics of living organisms
They can react to their environment, often heal themselves when damaged
They grow by taking nourishment from environment and processing it into energy
They reproduce, passing along some of their characteristics to offspring
They have the capacity for genetic change, can evolve from generation to generation and adapt to a changing environment
Exceptions to Definition of Life
Viruses:
Cannot reproduce without help
Viruses transfer their genetic material into living cells, genetic material takes over cell, and the cell starts producing copies of the virus
Somewhere between living and non-living
Stars
React to gravity of neighbors
Can grow (accrete mass), generate energy, and "reproduce" by triggering formation of new stars
Assumptions of Mediocrity
Central idea of chemical evolution is that life evolved from non-life
Case for extraterrestrial life comes from "Assumptions of Mediocrity"
Life on Earth depends on a few basic molecules
Elements that make up these molecules are common (more or less) to all stars
Laws of science we know apply to the entire universe- so that life must have evolved elsewhere
Organic Life
Organic = carbon-based
Complex molecules arise from organic molecules
Amino acids (form proteins, which control metabolism) and nucleotide bases (form genes) made out of organic molecules
Amino acids can arise from:
chemical processes in Earth's atmosphere (Urey-Miller experiment in 1953)
Meteorites - interstellar clouds contain many complex molecules and may contain an amino acid
Read more in book
Building Blocks of Life in the Solar System
Murchison meteorite fell to Earth in 1969, Fig. 28.6
Contains 22 amino acids normally found in living cells
Organic molecules in Hale-Bopp
Comets may have brought much of Earth's water
See chapters on planets for discussion of life on other bodies
Life on Earth
99% of life is composed of 4 molecules:
Hydrogen, oxygen, nitrogen, and carbon
3 most common molecules: ammonia, methane, carbon dioxide,
What composition is the composition of Earth's life similar to?
The Sun!! and most Stars
Not Earth's crust (mostly silicon ), the Earth itself is made of very little carbon
Extrasolar Planets
Since 1995, over 90 planets outside of our solar system now known (see section 15.5)
Identified by star's wobble due to gravitational tugs from the orbiting planets
Many of these extrasolar planets are so called "hot Jupiters"
Very close to the star, but masses similar to Jupiter
None of the planets looks like Earth
Habitable Zone
Planet must be massive enough to retain an atmosphere, but not too massive
Planet must be at the right temperature
Be in a stable orbit (fairly circular)
Fig. 28.10 and 28.11
Drake Equation
Number of technological civilizations =
rate of star formation over lifetime of Galaxy
fraction of stars having planets
average number of habitable planets in planetary systems
fraction on which life arises
fraction on which intelligence evolves
fraction of these that develop a technological society
average lifetime of a technologically competent civilization
Drake Equation
Fig. 28.9
Search for Extraterrestrial Life
Search for radio signals similar to those that Earth produces
Search in water hole - region of EM spectrum that Galaxy and stars are "quiet", water is assumed to be basic building block of life
Fig. 28.13, 28.14
Search for Extraterrestrial Life
Fig. 28.13, 28.14
Summary
Process of cosmic evolution
Drake equation- evaluate the chances of findling life elsewhere in the solar system
Understand the various probabilities in the Drake Equation
How are astronomers searching for life
Pioneer 10 Plaque
Can you figure out our message to alien life?