Astronomy review for final

Key Concepts: Life and Habitability

• Definition of Life: Self-contained chemical system capable of Darwinian evolution.

  • Practical Detection: Indicators include growth, reproduction, metabolism, and movement.

  • Exceptions: Examples include mules, fire, crystals, stars, and computer viruses.

• Universe Formation: Originated from a big bang, leading to a universe with stars that have life cycles.

  • Life Cycle of Stars: Stars form from gas, burn hydrogen, explode, and die, creating heavy elements necessary for life.

  • Carl Sagan Quote: "We are star stuff."

• Earth Formation: Earth formed around the Sun; categorized into:

  • Inner Planets: Terrestrial, small, rocky (Mercury, Venus, Earth, Mars).

  • Outer Planets: Jovian, gas giants (Jupiter, Saturn, Uranus, Neptune).

• Age of Earth: 4.5 billion years.

  • Oldest Rocks: 3.8 billion years old.

  • Oldest Evidence of Life: Also 3.8 billion years old.

Advantages of Water

• Liquid Range: Broad range where water remains liquid.

• Solvent Properties: Acts as a universal solvent due to being a polar molecule.

• Physical Characteristics: Ice floats, allowing aquatic life to survive winter.

Advantages of Carbon

• Bonding Abilities: Forms stable bonds, allowing creation of long chains and multiple functional groups.

• Organic Compounds: Life utilizes carbon to create diverse organic compounds with specific biological functions.

Types of Organic Molecules

• Sugars: Polysaccharides

• Fatty Acids: Lipids

• Amino Acids: Proteins

• Nucleotides: Nucleic acids

Cellular Structure of Life

• Cell Composition: All life is composed of cells; variations exist (e.g., cell walls, nuclei in eukaryotes).

• Evidence for Common Ancestor: Universal characteristics include DNA, ATP, genetic code, and chirality shared among all life forms on Earth.

Types of Organisms

• Nutrition Modes: Chemotrophs, autotrophs, heterotrophs, and extremophiles.

  • Extremophiles: Adapted to extreme conditions (high/low temperature, pressure, pH, salinity, radiation).

  • Types: Thermophiles, barophiles, acidophiles, halophiles, radiophiles.

Tree of Life

• Classification: Bacteria, Archaea, Eukarya.

• Common Ancestors: Organisms with common genes likely share a common ancestor.

The Oldest DNA

• Includes genes for thermophilic enzymes, indicating that thermophilic organisms are near LUCA (Last Universal Common Ancestor).

• Microbial Dominance: Microbes are the most common form of life.

Requirements for Life

• Biogenic Elements: SPONCH (Sulfur, Phosphorus, Oxygen, Nitrogen, Carbon, Hydrogen).

• Liquid Water: Essential for life.

• Energy Sources: Currently, sunlight is the primary energy source; early life may have used chemical energy from hydrothermal vents.

• Origins of Organics: Miller-Urey experiments, comets, meteorites, and hydrothermal vents can be sources of organic compounds.

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Plate Tectonics and CO2 Cycle

• Mechanism: Convection inside Earth drives plate tectonics and sea-floor spreading; subduction recycles CO2 stored in carbonate rocks.

• CO2 Cycle Steps:

  • Emission from volcanoes.

  • Absorption in rain to form carbonate rocks.

  • Plate tectonics move carbonate rocks under continents.

  • Breakdown into CO2 during subduction, replenishing atmosphere.

Feedback Mechanism

• Acts as a thermostat, maintaining temperature equilibrium.

  • Survived Snowball Earth due to CO2 cycling.

Origin of Life Theories

• Possibly from:

  • Warm ponds.

  • Hot vents.

  • Extraterrestrial infection (panspermia).

• RNA World Hypothesis: States that RNA served as both information carrier and catalyst.

Key Concepts of Life Evolution

• Evolution Mechanism: Changes occur through variation, inheritance, and selection.

• Examples of Evolution:

  • Melanism in peppered moths.

  • Myxomatosis in rabbits showing adaptation.

  • COVID evolution (more contagious, less deadly).

• Cambrian Explosion: Emergence of complex multicellular life about 570 million years ago.

Challenges to Evolution

• Low probabilities, gradual changes not observed, and the complexity of life forms.

Life on Other Worlds: Venus

• Past Conditions: Once more conducive to life before greenhouse effect.

• Potential Migration: Surface life may have moved to clouds to survive.

• Cloud Life: Would need to adapt to acidic conditions and UV radiation, possibly evolving its own sunscreen.

Life on Mars

• Current State: Cold, dry, thin atmosphere, sterilized by UV.

• Evidence of Water:

  • Gullies, RADAR detecting permafrost, ancient lake beds.

  • Past water flow suggested by geological features.

Viking Lander Findings

• Active chemistry detected, but results inconclusive for biological processes.

• Importance of Control Experiments: Critical to validate findings.