chapter 18 life in the universe. galaxyrise over alien planet by d. berry
TRANSCRIPT
Chapter 18Life in the Universe
Chapter 18Life in the Universe
Galaxyrise Over Alien Planet by D. Berry
Cosmic evolution - phases in the history of the universe
Cosmic evolution - phases in the history of the universe• Particulate
• Galactic
• Stellar
• Planetary
• Chemical
• Biological
• Cultural
Figure 18.1Arrow of Time
Living organismsLiving organisms
• React to environment and can often heal themselves when damaged
• Grow
• Reproduce
• Genetic change and evolution to adapt to a changing environment
Assumption of mediocrityAssumption of mediocrity
• Life on earth depends on a few basic molecules
• Elements in these molecules are common to all stars
• Laws of science same everywhere
• Life must have originated elsewhere than on earth
Chemicals on earth before life formed
Chemicals on earth before life formed
• Outgassing in early earth produced hydrogen, nitrogen and carbon compounds
• Ammonia, methane, carbon dioxide and water formed
Energy inputEnergy input
• Energy from radioactivity, volcanism, lightning, UV radiation and meteoritic impacts modified chemicals
• Formed amino acids and nucleotide bases
• Organic (carbon-based) molecules that are the basis of life
Amino acids and nucleotides
Amino acids and nucleotides
• Amino acids build proteins, which control metabolism
• Sequences of nucleotide bases form genes, which are part of DNA molecules
• DNA controls synthesis of proteins and determines characteristics of living organisms
• Genes carry hereditary information to the next generation
Figure 18.2DNA Molecule
Miller-Urey experimentMiller-Urey experiment
• 1953 - took primordial chemicals, input energy, and generated amino acids
• A later experiment generated nucleotide bases
• Did not produce life, but did synthesize biological molecules
• Demonstrated chemical evolution
Figure 18.3Miller-Urey Experiment
Figure 18.4Chemical Evolution
Interstellar origin?Interstellar origin?
• Some scientists claim organic material came from interstellar space
• Experiment exposed icy mixture of water, methanol, ammonia and carbon monoxide to UV radiation
• Complex organic molecules formed
Figure 18.5Interstellar Globules
Diversity and cultureDiversity and culture
• Simple one-celled life appeared on earth about 3.5 billion years ago
• More complex one-celled life appeared about 2 billion years ago
• Multicelluar organisms appeared about 1 billion years ago
• Insects, reptiles, mammals, etc.• Biological evolution led to the strongly favored
trait of intelligence• Cultural evolution followed
Figure 18.6LLife on Earth
Figure 18.6RLife on Earth
Life as we know itLife as we know it
• Means carbon-based life originating in liquid water environment
• Did it happen elsewhere in the solar system?• No on Moon or Mercury - no protective
atmosphere• Not on Venus - atmosphere too dry and hot• Jovian planets have no solid surface, Pluto too
cold• Europa and Titan possibilities• Mars a possibility
Figure 18.7Murchison Meteorite
Alternative biochemistriesAlternative biochemistries
• Carbon is basis of life forms on earth• Maybe silicon could be basis of life
forms• Ammonia could be an alternative
instead of water
Intelligent life in our GalaxyIntelligent life in our Galaxy
• Distances in Galaxy too great to detect life with current technology
• Instead rely on estimating likelihood of intelligent life in Galaxy
Drake EquationDrake Equation
• Named after Frank Drake, who pioneered a probability type calculation
Number of technological civilizations in galaxy isNumber of technological civilizations in galaxy is
• Rate of star formation X• Fraction of stars having planetary systems X• Average number of habitable planets in those
planetary systems X• Fraction of those planets on which life arises X• Fraction of those planets on which intelligent life
evolves X• Fraction of those planets developing technology X• Average lifetime of a technological civilization
Figure 18.9Drake Equation
Rate of star formationRate of star formation
• Roughy 100 billion stars in Galaxy• Galaxy has been around 10 billion years• 10 stars per year forming
Fraction of stars having planetary systems
Fraction of stars having planetary systems
• Informed guess - fraction of 1 or so
Number of habitable planets per planetary system
Number of habitable planets per planetary system
• Determined by distance to star (too hot or cold)• Determined by spectral class of star• Affected by orbit of star and if star in orbit in a
binary star system• Depends on position in Galaxy - supernovae
damage and gravitational effects of close-encounter stars
• Estimate 1/10 (1 habitable planet per 10 planetary systems)
Figure 18.10Stellar Habitable Zones
Figure 18.11Galactic Habitable Zone
Figure 18.12Binary-Star Planets
Fraction of habitable planets on which life arises
Fraction of habitable planets on which life arises
• Can make guesstimates from chemical formation• Optimistically assign this 1
Fraction of life-bearing planets on which intelligence arises
Fraction of life-bearing planets on which intelligence arises
• Any hint of intelligence is highly favored by evolution
• Guess this fraction to be 1
Fraction of planets on which intelligence develops technology
Fraction of planets on which intelligence develops technology
• Technological societies developed independently at several locations on earth
• Give this factor a 1
Average lifetime of a technological civilization
Average lifetime of a technological civilization
• Modern civilization for only 100 years or so• Maybe 1000 years?• Multiply all of the factors together and end up with
there should be 1000 technological civilizations scattered throughout our Galaxy
• It is unlikely there is time enough for these civilizations to communicate
Search for Extraterrestrial Intelligence
Search for Extraterrestrial Intelligence
• If technological civilizations last 1 million years, there are 1 million in existence
• Average about 100 light-years apart• 200 years for two-way communication• In current fastest space ship, trip there and back
would take 1 million years
Figure 18.13Pioneer-10 Plaque
Radio searchRadio search
• Radio waves best for communication - not scattered by dusty interstellar space
• We would not broadcast to other stars• We would passively “listen” toward F, G and K
stars near the sun• Earth is currently stronger (man-made) radio
emitter than the sun
Figure 18.14Earth’s Radio Leakage
Most probable radio wavelengths
Most probable radio wavelengths
• Near 20 cm - H emission is so common• H radiates at 21 cm• OH radiates near 18 cm• They together make water, which our life form is
based on• Wavelengths between 18 and 21 cm are called a
“water hole”• Galactic background minimized
Figure 18.15Water Hole
SETISETI
• Search for Extraterrestrial Intelligence• Project Phoenix searched in 1-3 GHz range• Nothing resembling intelligence yet detected
Figure 18.16Project Phoenix
Consequences of two civilizations meeting
Consequences of two civilizations meeting
• Consider the history of earth• What happened whenever a more “advanced”
civilization met a less “advanced” civilization?