Hadean Eon: Earth was hot and molten around 4.6 billion years ago with volcanic activity.
Early Atmosphere: Reducing atmosphere with gases like hydrogen, methane, and ammonia; no oxygen.
Sources of Organic Molecules
Extraterrestrial: Organic molecules may have arrived via meteorites and comets.
Terrestrial: A reducing atmosphere may have supported the formation of organic molecules, such as amino acids.
Experimental Evidence – Prebiotic Chemistry
Miller–Urey Experiment: Simulated early Earth conditions, producing amino acids and organic molecules.
Metabolic Evolution
Autotrophs: Used inorganic compounds for energy; may have relied on a reductive citric acid cycle.
Heterotrophs: Used organic molecules from the environment.
Oxygenic Photosynthesis: Added oxygen to the atmosphere during the Archaean and Proterozoic eons.
Carbon and Nitrogen Fixation: Allowed life to grow and recycle essential elements.
Evolution of Genetic Systems
RNA World Hypothesis: RNA may have been the first genetic material, storing information and catalyzing reactions.
Challenges: Unclear how ribose formed; clay surfaces may have helped RNA chains.
DNA and Proteins: Took over later for stability and diversity.
Cell Formation and Membranes
Protocells: Fatty acid membranes formed compartments, speeding up chemical reactions.
Origin of Cellular Life: Enclosed organic molecules within protocells formed the first living cells.
Universal Common Ancestry and Domain Evolution
LUCA (Last Universal Common Ancestor): Gave rise to Bacteria, Archaea, and Eukarya.
Eukarya: Likely evolved from within Archaea; Asgard Archaea may be closest relatives to eukaryotes.
Eukaryotic Supergroups and Diversity
Five Supergroups: Excavata, SAR, Archaeplastida, Amoebozoa, and Opisthokonta.
Monophyletic Clades: Most supergroups include all descendants of a common ancestor.
Compartmentalization and Origin of Eukaryotes
Prokaryotic Dominance: Bacteria and Archaea were the only life-forms for over a billion years.
Eukaryotic Features: Eukaryotes developed internal compartments.
Evolution of the Endomembrane System
Key Innovations: Internal membranes like the nuclear envelope, ER, and Golgi apparatus.
Evolutionary Origin: Structures likely formed through plasma membrane infolding.
Endosymbiosis and Organelle Origin
Mitochondria: Evolved from Rickettsia-like bacteria.
Chloroplasts: Originated from cyanobacteria; red and green algae acquired them directly, while brown algae likely obtained them secondarily by engulfing red algae.
Multicellularity and Cell Specialization
Evolutionary Advantage: Allowed development of tissues and organs.
Cell Differentiation: Specialized cells worked together.
Independent Origins: Evolved separately in several lineages.
Sexual Reproduction
Evolutionary Innovation: Introduced recombination of genetic material.
Genetic Diversity: Increased variation through meiosis and crossing over.
Cambrian Explosion and Rapid Diversification
Geological Context: Began about 542 million years ago.
Biodiversity Surge: Rapid expansion of multicellular animal life.
Colonization of Land
Initial Transition: Plants, followed by animals.
Atmospheric Conditions: Oxygen levels rose, leading to the formation of the ozone layer.
Key Adaptations: Development of lungs (animals) and stomata (plants).