Lesson 7: Origins of Life on Earth

Spontaneous Generation

Belief that life arises regularly from non-life.

Biogenesis

Life only comes from lifeand cannot arise from non-living matter.

Earth’s formation

4.6bya

Condensing from vast cloud of dust and rocks that surrounded the sun

• No life yet and was bombarded with ice and rocks

• the heat from collision so intense, water was evaporated from ice

The first atmosphere formation

3.9bya

• Reducing atmosphere (no oxygen O2)

• lots of water vapour and the compounds of volcanic eruptions, (N2, CO2, CH4,NH3,H2,H2S)

• Earth started to cool, oceans formed as water vapour condensed, most H2 escaped to space

The Theory of the Origin of Life

1. Abiotic (non-living) synthesis of small organic molecules

2. Synthesis of monomers into polymers (macromolecules)

3. Packaging of molecules into protocells → first membrane bonded vesicles

4. origin of self-replicating molecules

Abiotic synthesis of small organic molecules

The spontaneous formation of organic monomers from inorganic compounds without the presence of living organisms.

• Key conditions: Required inorganic gases (H2OH2​O, CH4CH4​, NH3NH3​, H2H2​) and energy from volcanic activity, lightning, or UV radiation

• Experimental support: The Miller-Urey experiment demonstrated that amino acids and other organic compounds could form under simulated early-Earth conditions

• Proposed locations: reducing atmosphere and deep-sea volcanic vents, and meteorites

Synthesis of monomers into polymers (macromolecules)

• Dripping amino acids (liquid form) or RNA nucleotides onto hot rocks/sand → molecules would spontaneously form polymers

  • Polymers were not the complex organic molecules in present day, but could function as a protein as catalyst for chem rxn

Packaging of molecules into protocells

The process by which organic molecules aggregate to form enclosed structures resembling cells (protocells), allowing for internal environments to develop. These protocells may have provided a platform for biochemical reactions leading to more complex life forms.

• vesicles can reproduce and divide on their own

• can grow without diluting their contents

• can absorb montmorillonite (clay produced from weathered volcanic ash) particles which may contain RNA

• Some can perform metabolic reactions using external source (hot rocks) of reactants

Origin of self-replicating molecules

• First genetic material is RNA (less stable), NOT DNA

• Ribozymes (basic RNA) can catalyze chem rxn

• An RNA world existence for a long time in which small RNA molecules were able to replicate and store info about the vesicles that carried them

• Eventually DNA produced → MORE STABLE molecule

Prokaryotes origin time

3.9 bya

• first single celled organisms

When the first real evidence of prokaryotes in Fossil Record appeared

3.5 bya - 2.1 bya

Time period when beginning of Oxidized atmosphere → reducing atmosphere changing

2.7 bya

• Oxy increased in water due to cyanobacteria spitting water molecules during photosynthesis

• Oxy reacts with dissolved iron, creating rust in ocean sediments and leading to a significant increase in atmospheric oxygen.

Eukaryotes appearance time period

2.1bya LOTS OF PROKARYOTES DIED OFF

Where did Eukaryotes come from?

• Endosymbiont theory suggests that eukaryotes originated from symbiotic relationships between different species of prokaryotes, where certain prokaryotic cells engulfed others but did not digest them, leading to a mutualistic relationship.

Multicellular Organisms time period

1.2 bya → when multicellular organisms first appeared on Earth, marking a significant evolution in complexity.

Larger multicellular organisms appearance time

575 mya