Origin of Life Theories

Study Notes

Several origin-of-life theories exist, based on mathematical and fossil evidence.

Abiogenesis suggests life's molecules formed from simple inorganic molecules near deep-sea vents.
Deep-sea vents emit hot gases and liquids that accumulate small molecules like hydrogen and minerals.
Reactions, aided by catalysts, produced life's molecules within these vents.
Scientists have replicated vent conditions to produce protocells.

Life may have started in oceans under ice, as amino acids are more stable at low temperatures.
Cold environments could have facilitated the emergence of life.

Earth is about 4.6 billion years old.
The universe began as a hot, dense point that exploded in the Big Bang.
Particles from the Big Bang formed stars and planets, including Earth.
Primitive Earth was bombarded by debris and lacked an atmosphere.
Temperatures reached 10 billion degrees Fahrenheit (5.5 billion degrees Celsius).
Volcanoes and meteor strikes further shaped Earth.
Meteorites delivered ice, carbon oxides, ammonia, methane, and hydrogen.
Chemical reactions at high temperatures led to the emergence of simple molecules about 3.7 billion years ago.

Alexander Oparin theorized in 1924 that life arose from simple molecules in a low-oxygen atmosphere.
Oparin suggested that the early atmosphere was reducing.
The first life forms were heterotrophic and originated in the oceans.
Early Earth lacked a protective atmosphere, leading to high ultraviolet radiation exposure.
Oparin studied coacervates, which are collections of organic molecules in water with a lipid membrane.
Coacervates are a type of protobiont, microspheres with a double-layered lipid membrane.
Protobionts can maintain their internal environment.
Oparin believed protobionts were precursors to living cells.
His research showed biomolecules within coacervates function efficiently in metabolic processes.
J.B.S. Haldane independently proposed similar ideas.
Haldane suggested ultraviolet radiation helped form simple organic molecules that evolved into more complex ones.

Stanley Miller and Harold Urey aimed to test Oparin's theory in 1953.
They simulated Earth's early atmosphere in a glass apparatus with interconnected bulbs, pumps, and cooling systems.
One bulb contained water to represent Earth's primordial soup.
The other bulb held methane, hydrogen, ammonia, and water vapor, and was fitted with electrodes.
Electric discharges simulated lightning and ultraviolet radiation.
After a week, the water changed color, indicating a reaction has occurred.
Analysis revealed that 15% of the methane converted to simple carbon compounds like formaldehyde and hydrogen cyanide.
These compounds then formed more complex molecules, including the amino acids alanine and glycine.
The experiment demonstrated that essential building blocks of life could evolve from simple molecules.
The experiment supported Oparin's theory.