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139 Cards in this Set
- Front
- Back
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Two paradigm-shifting discoveries that have stimulated astrobiology
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Detection of extrasolar planets
Life in extreme environments |
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Number of stars in the Milky Way
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200 billion
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Distance of Andromeda Galaxy
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2 million light-years
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Distance of Virgo Clusterer
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60 million light-years
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Sun: six most abundant elements
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Hydrogen
Helium Oxygen Carbon Neon Nitrogen |
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Earth: four most abundant elements
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Oxygen
Iron Silicon Magnesium |
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Air: four most abundant elements
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Nitrogen
Oxygen Argon Carbon |
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Ocean: four most abundant elements
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Hydrogen
Oxygen Chlorine Sodium |
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Human: four most abundant elements
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Hydrogen
Oxygen Carbon Nitrogen |
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Carbon: Number of possible bonds
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Four
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Organic compounds are made up of what type of bond?
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C-H bonds
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Astronomers have detected how many species of molecules in interstellar clouds?
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150
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Largest interstellar molecule discovered has how many atoms?
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13
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Why is the Murchison meteorite famous?
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Believed to represent early solar system; had amino acids
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Problems with Si-based life
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Si-Si is a weaker bond
Bonds only at high temps Si usually ends up bonding with O Rarer than Carbon |
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Benefits of Liquid Water
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Good solvent
Exists at good temperature High heat capacity Abundant Expands as it freezes High surface tension |
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Ingredients of Life
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Carbon
Liquid Water Energy |
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Molecular Composition of Life: Inorganic
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1 percent of weight; 20 types
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Molecular Composition of Life: Small Organics
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7 percent of weight; 750 types
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Molecular Composition of Life: Large Organics
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22 percent of weight; 5000 types
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Types of Macromolecules
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Lipids
Carbohydrates Proteins Nucleic Acids |
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Lipids: Characteristics
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One hydrophobic end
One hydrophilic end Compact way to store energy Useful in membranes |
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Carbohydrates: Characteristics
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Hydroxyl groups
Soluble in water Sugars Store energy |
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Proteins: Characteristics
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Most complex macromolecule
Long chains of amino acids |
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Life uses how many amino acids?
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20
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Life uses how many proteins?
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10,000
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Nucleic Acids: Characteristics
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Largest macromolecule
Made up of nucleotides A five-carbon sugar molecule One or more phosphate groups An N-containing compound |
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DNA: Characteristics
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Two long molecular strands
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Base pairs: what pairs with what?
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A with T
C with G |
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Human DNA is made up of how many base pairs?
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3 billion
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Human DNA has how many genes?
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30,000
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Human genes have how many base pairs?
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3,000
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RNA: What sugar takes place of which of DNA's sugars?
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U takes the place of T
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The simplest cell contains what?
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DNA
Salt solution (cytoplasm) Enzymes Ribosomes Cell membrane |
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How many cells do humans have?
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10^13
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Causes of mutation
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cosmic rays
chemical agents errors in DNA-copying |
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A broad recipe for life
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1. Raw ingredients
2. A process that can make macromolecules 3. Creation of a self-replicating macromolecule 4. The formation of cells 5. Evolution |
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Miller-Urey: Compounds used
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H2,H2O, NH3 (ammonia), CH4 (methane)
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Miller-Urey: Result
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Brown gunk formed in water
Brown gunk was organic matter like amino acids |
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Miller-Urey: Significance
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Many of the organic compounds needed for life can be naturally/easily made from chemical reactions involving a few simple molecular species
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Chirality
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The "handedness" of molecules like amino acids
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All Earth life uses ____-handed amino acids
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left
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Polymerization: Definition
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The process by which basic organic molecules formed into macromolecules.
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Polymerization: Prevailing theory
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Polymers formed on clay by ponds that kept drying and freezing.
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DNA: Prevailing theory of its formation
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RNA World
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Molecular Phylogeny
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An approach to understanding the origin of life by studying the genetic record.
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Three main branches of life
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Archaea, Bacteria, and Eukarya
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A useful phylogenetic tree is based on what?
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The ribosomal RNA found in almost all cells
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Species closest to the root of the rRNA phylogenetic tree.
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Thermophiles/hyperthermophiles
Like the organisms populating deep-sea vents today |
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Habitable zone: Definiton
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The range of distances from a star for which it is warm enough for liquid water to exist on a planetary surface.
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Habitable zone equations
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1. Energy = luminosity/(4piDistance^2)
2. Energy x albedo |
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Temperature equation
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Temp = Power/(4pi[constant]Radius^2)
"Radius" refers to the radius of the planet. |
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Using the temperature equation puts the Earth's temperature at ___. Why?
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255K (well below the freezing point of water and the mean surface temp)
Why: the equation does not consider greenhouse gases. |
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Without greenhouse gases, the habitable zone would extent from ___ to ___.
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.47 AU to .87 AU
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Venus' surface temperature
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750 K
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Venus' atmosphere is ____ times denser that of Earth
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100
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How would higher planetary albedos affect the habitable zone?
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Push the inner edge toward the star.
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How would more planetary greenhouse gases affect the habitable zone?
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Push the outer edge away from the star.
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The inner edge of the habitable zone in the solar system is what distance from the sun?
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.95 AU
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The outer edge of the habitable zone in the solar system is what distance from the sun?
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1.5 AU
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What determines the inner edge of the habitable zone?
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Stellar luminosity
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What determines the outer edge of the habitable zone?
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Greenhouse gas
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More Carbon Dioxide does what to the extent of the habitable zone?
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Increases it
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The average protein has how many amino acids?
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100
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Theories explaining how Earth got its water
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1. Earth accreted as a dry object and got its water through cometary impact
2. From the water-bearing minerals in the planetesimals that build it |
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Comets: composition
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Water ice
Frozen gases like CO2 Grains of rocky and organic material |
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Comets: size
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up to about 10 km
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Comets: sources
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Oort Cloud
Kuiper Belt |
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Deuterium: definition
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A rare isotope of Hydrogen
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Deuterium: How does the D/H ratio in Earth's oceans compare to the ratio in comets?
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The D/H ratio in oceans is about half that of comets.
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Deuterium: What is the significance of the discrepancy between the D/H ratio in Earth's ocean and in comets?
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It discredits the idea that most water on Earth came from comets.
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Outgassing: definition
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The process by which geological processes in the early Earth driven water from its rocks to its atmosphere.
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Many meteorites contain what that is important to the origin of water on Earth?
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Water-bearing minerals
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Early Earth: Atmospheric composition
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Nitrogen, Carbon Dioxide, some water vapor and sulfur oxides, trace amounts of oxygen
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Early Earth: the origin of trace atmospheric oxygen in early Earth
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Sun's UV radiation breaking water molecules into oxygen and hydrogen.
Light H atoms would escape the atmosphere. O atoms would stay and form atmospheric oxygen and ozone. |
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Early Earth: why was the formation of even a little atmospheric ozone important?
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Protected possible life from UV radiation.
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Without atmospheric protection, life can survive UV radiation by...
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...living in water or sediment.
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Oldest claimed fossil is of what and how old is it?
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Cyanobacteria; 3.5 billion years
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Cyanobacteria: definition
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Oldest form of life discovered
Prokaryotes Known as blue-green algae today Build up stromatolites Produce oxygen through photosynthesis |
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The carbon isotopes that, in relative abundance, act as a tracer of life.
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13C/12C
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The macromolecular material in which organic molecules in ancient rocks is preserved.
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Kerogen
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Cyanobacteria prefer which carbon isotope over which?
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12C over 13C
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What two life forms were probably the first?
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Thermophiles or cyanobacteria
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Origin of oxygen on Earth
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Cyanobacteria
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When did the first single-celled eukaryotes appear?
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2 billion years ago
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When did the first multicellular organisms appear?
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1 billion years ago
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What is quite probably the most significant biologically driven event in Earth's history?
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Creation of an oxygen-rich atmosphere.
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What four events (in the proper order) dramatically shaped the evolution of life on Earth?
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1. Development of O-rich atmosphere
2. Snowball Earth Glaciations 3. Permo-Triassic Mass Extinction 4. K-T Mass Extinction |
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Snowball Earth
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A series of as many as four periods in which Earth was frozen over for 10 million years or more.
Surface temp: -50C Ocean Ice thickness: 1 km |
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Cambrian Explosion
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An explosion of variety in forms of life following the Snowball Earth glaciations
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Permo-Triassic Mass Extinction
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Most catastrophic of all mass extinctions.
Caused by a sudden release of greenhouse gases, poisoning the atmosphere and causing intense heating. |
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K-T Mass Extinction
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Most recent mass extinction.
Due to the impact of an asteroid about 10 km in diameter and with an explosive yield of 100 million megatons of TNT), blacking out the sky and thereby killing the plants. |
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K-T Mass Extinction: Evidence
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Thin layer of iridium with soot particles in Earth's crust.
Crater in the Yucatan Peninsula in Mexico |
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Asteroid that will pass by Earth in 2029.
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Apophis
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Evolutionary ages: age of mammals
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Cenozoic
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Evolutionary ages: age of dinosaurs
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Mesozoic
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Evolutionary ages: age of trilobites
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Paleozoic
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Evolutionary ages: list them
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1. Archaean
2. Proterozoic 3. Paleozoic 4. Mesozoic 5. Cenozoic |
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What species of bacteria survived harsh conditions in space?
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Streptococcus
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What conditions did Streptococcus survive?
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Space launched
3 years of space vacuum Radiation exposure Deep-freeze No nutrient, water, or energy |
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Most heat-loving hyperthermophile known lives best at what temperature?
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105 C
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Astronomer who accidentally fueled the thought that there were canals on Mars
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Giovanni Schiaparelli
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First spacecraft to make a successful flyby of Mars
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Mariner 4
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How does the radius of Mars compare with that of Earth?
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Half that of Earth
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How does the mass of Mars compare with that of Earth?
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10% that of Earth
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How does the surface gravity of Mars compare with that of Earth?
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37%
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How long is the Martian day?
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About the same as an Earth day
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How long is a Martian year?
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1.88 Earth years
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Composition of Martian atmosphere
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95% CO2
Less than 3% each of: N2, Ar, O2 |
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Mars receives ___ times less sunlight than Earth does.
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2.3
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Due to a very thin atmosphere, the Martian greenhouse effect warms the planet _____.
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5 C
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Largest volcano in the solar system
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Olympus Mons
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The upper crust of the Martian ice caps is made of...
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Dry Ice
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If the Martian ice caps melted, the planet would be covered in water ____ deep.
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11 meters
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Each Martian year, the polar ice caps on Mars...
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shrink
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Why did Mars end up unlike Earth?
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1) Weaker gravitational field
2) More rapid cooling of molten interior |
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The first direct test of life on Mars was what project?
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The Viking Project
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The Viking Project assumed what about Martian life?
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That it is carbon-based.
That is has chemical composition like Earth life. That it metabolizes simple organic compounds. |
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Results of the GCMS
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Martian soil has virtually no organic material
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Three Viking biology experiments
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GEX
LR PR |
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Viking experiments: GEX
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Touched soil with nutrients and measured gas products
Result: A lot of oxygen produced, but control had same result. |
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Viking experiments: LR
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Use nutrients with radioactive carbon atoms.
Result: Sudden rise in gas radioactivity. With more nutrients, decrease in radioactivity followed by a slow rise. Control did not show same result. |
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Viking experiments: PR
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Soil sample placed in simulated Martian atmosphere. Tested to see if any organisms had ingested radioactive Carbon.
Result: Showed that radioactive Carbon had apparently been ingested. But control showed same result. |
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Lessons from Viking
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1. It is difficult to distinguish biochemical reactions from chemical reactions
2. Even the hardiest of Earth extremophiles would find it tough to adapt to the Martian surface 3. Results don't rule out life on Mars |
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Why didn't Viking rule out the possibility of life on Mars?
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1. Strong evidence of underground water
2. Water may be closer to the surface in the polar regions |
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Phoenix
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Dug a trench in northern polar region
Found chunks ice that sublimated away over time Found perchlorates in soil |
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What type of extremophile could thrive in the watery Martian underground?
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SLiME
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Meteor from Mars, possibly with fossilized life
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ALH 84001
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ALH 84001 was discovered where?
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Antarctica
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Why have the majority of the world's collection of meteriorities come from Antarctica?
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Easy to find because:
Largely featureless surface Lack of human activity |
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Group of meteorites from Mars
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SNC Meteorites
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How many SNC meteorites are there?
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30
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How do we know SNC meteorites are from Mars?
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They have pockets of gas that match the composition of the Martian atmosphere as measured by Viking.
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The claim of ancient life on ALH 84001 is based on what five pieces of evidence?
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1. Carbonate resembles crystals produced by bacteria on Earth
2. Carbonate structures that look like fossils 3. Small particles of magnetite that resemble magnetite made by bacteria on Earth 4. Formation of carbonate, iron sulfide, and FE3O4 (iron oxide) minerals in globules 5. Globules contain complex organics known as polycyclic aromatic hydrocarbons that have been identified as the decay products of Earth microbes |
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The Martian Face was found where?
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Plains of Cydonia
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Jupiter's four largest moons
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Io
Europa Ganymede Callisto |
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Jupiter's moons: composition
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Io: rock
Europa: mostly rock with some ice Ganymede, Callisto: ice mixed with rock |
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Io
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Caught in a tug of war between the gravity of Jupiter and Europa/Ganymede
Slightly elliptical orbit Immense tidal heating making it the most volcanically active place in the solar system |
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Europa
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Some tidal heating
Young surface Ice with more ice, liquid water, or slush beneath |
