Origins of cells

Prebiotic Earth Conditions

• Early Earth had no oxygen, intense UV radiation, high methane and CO₂ levels—ideal for spontaneous formation of organic molecules like amino acids.

Definition of a Cell

• Cells are the smallest units of life; they're self-sustaining, maintain order, can reproduce, and live outside organisms, unlike organelles.

Disproving Spontaneous Generation

• Louis Pasteur disproved the idea that life could arise spontaneously; today, we know that cells only arise from pre-existing cells.

Requirements for the First Cell

• Needed metabolism, polymer formation (e.g., proteins, DNA), compartmentalization, and self-replicating molecules.

Miller-Urey Experiment

• Simulated prebiotic Earth conditions and showed amino acids (building blocks of life) could form spontaneously, supporting abiogenesis.

Formation of Membranes

• Phospholipids spontaneously form bilayers in water, creating vesicles—key for compartmentalization and selective permeability.

RNA as First Genetic Material

• RNA likely preceded DNA: it's self-replicating, catalytic, mutates quickly (creating genetic diversity), and is found in RNA-only viruses.

LUCA – Last Universal Common Ancestor

• All life likely descended from LUCA, shown by shared use of DNA, similar ribosomes, and conserved genetic mechanisms.

Dating the Origin of Life

• Carbon dating suggests LUCA arose ~4.1 billion years ago, while genomic comparison suggests ~4.5 billion years ago; both are valid but contestable.

Possible Location of LUCA