(3) Unit 7 Topic 13 Packet

Origins of Life on Earth

• Formation of Earth

  • Earth formed approximately 4.6 billion years ago.

  • Early Earth was unsuitable for life until around 3.9 billion years ago.

  • Earliest fossil evidence (3.5 billion years ago): cyanobacteria, which are considered our ancient ancestors.

Early Hypotheses on the Origin of Life

• Discovery of ancient cyanobacteria spurred scientific inquiry into life’s origins.

• Proposed Mechanisms for Organic Molecule Formation:

  • Inorganic Molecules to Organic Molecules: Early Earth’s inorganic molecules may have synthesized organic molecules through available energy and oxygen.

  • Extraterrestrial Sources: Organic molecules may have been delivered to Earth by meteorites or other celestial events.

The Miller-Urey Experiment

• Background: Conducted by Stanley Miller and Harold Urey to test conditions on early Earth.

• Hypothesis: Early Earth's atmosphere consisted of hydrogen, methane, ammonia, and water.

• Experiment Setup:

  • Gases simulating the primitive atmosphere with added electric sparks to mimic lightning.

  • Inclusion of a condenser to represent oceans and a heat source.

• Findings: Formation of organic compounds and amino acids as a result of the experiment.

• Controversy: Debate exists regarding contamination and the reliability of results.

• Conclusion from Experiment: Organic molecules acted as foundational building blocks for macromolecules (carbohydrates, proteins, lipids, nucleic acids).

RNA World Hypothesis

• Proposal: Suggests that RNA was the first genetic material, preceding DNA.

• Significance: This hypothesis helps explain pre-cellular stages of life development.

Endosymbiotic Theory Review

• Concept: Mitochondria and chloroplasts may have been engulfed by early eukaryotic cells.

• Supporting Evidence:

  • Mitochondria and chloroplasts possess their own circular DNA and double membranes, indicating they might have originated from independent prokaryotic organisms.

• Relation to Life's Origins: Suggests a gradual evolution from simpler forms to complex life.

Exam Preparation Recommendations

• Emphasis on reviewing all previous units and understanding key concepts.

• Encourage practice via AP Classroom, supplemental texts, and review books.

• Suggestions to highlight areas of strength and weakness for targeted study.

Conclusion

• Wrap-up of Unit 7 and anticipation of the upcoming Unit 8 video.

• Reminders for proactive exam preparation.