Primate Evolution and Earth's History

Primate Evolution and Origins of Life

• Humans diverged from other primates around 2 million years ago.
• Distinct emergence of birds, reptiles, and mammals occurred between 200 and 500 million years ago.
• Multicellular life forms began around 1 billion years ago, with eukaryotes appearing 2 billion years ago.
• Prokaryotic cells, such as bacteria, date back approximately 3.5 billion years, evidenced by ancient bacterial fossils.

Beginnings of Earth

• Earth formed about 4.5 billion years ago from a molten mass and developed chemically-rich oceans through cooling and water condensation.
• Theories about the origin of life remain unproven, with no definitive theories, only hypotheses.
• Key questions about life's origin focus on raw materials, formation of isolated cells, and the structure of early genomes.

Conditions of Early Earth

• Early Earth lacked a substantial atmosphere; gases dissipated quickly into space.
• The impact of a celestial body named Theia contributed to the formation of the Moon and a nascent atmosphere.
• Continuous meteoric bombardment induced violent volcanic activity, releasing water vapor, CO2, and ammonia into the atmosphere.

Organic Compound Synthesis

• First life forms appeared between 3.8 and 2.5 billion years ago; the composition of the early atmosphere is still debated.
• Hypotheses suggest an initially reducing atmosphere rich in water vapor and volcanic gases facilitated organic compound formation.
• The Miller-Urey experiment demonstrated that organic molecules could form abiotically in a reducing atmosphere, producing amino acids and other carbon compounds.

Formation of Protocells

• Protocells are aggregates of abiotically produced molecules, exhibiting simple reproduction, metabolism, and the ability to maintain internal conditions.
• A membrane is essential for encapsulating organic materials, requiring a mechanism for division and growth.
• Phospholipids can self-organize into membranes, potentially forming micelles in hydrothermal vent environments.

Vesicle Dynamics

• Vesicles can encapsulate various molecules, including amino acids and RNA, which suggests potential mechanisms for early cellular structures.
• Micelles can fuse and form long tubes which may break into smaller vesicles, aiding in replication processes.

Panspermia Hypothesis

• Suggests life or precursors to life may have been delivered to Earth via meteorites or cosmic dust.
• Complex organic molecules, like amino acids, have been detected on meteorites, indicating extraterrestrial origins.

Emergence of Genomes

• The initial genetic material is believed to be RNA, due to its reactivity and versatility compared to more stable DNA.
• RNA molecules, known as ribozymes, can catalyze their own replication, potentially leading to the evolution of early life forms.
• An "RNA world" may have existed, where RNA was the primary molecule for genetic information and catalysis before the advent of DNA.

Transition to DNA

• DNA emerged as a more stable genetic material compared to RNA, due to its structural differences that prevent degradation through reactions facilitated by RNA's hydroxyl groups.