The solar system is estimated to be 6.6 billion years old.

Earth is estimated to be 4.1 billion years old.

NH3 Ammonia .1% CH3 Methane .1% CO2 Carbon Dioxide 92.2% N2 Nitrogen 5.1% O2 Oxygen 0%

NH3 Ammonia Trace CH3 Methane Trace CO2 Carbon Dioxide .03% N2 Nitrogen 78.1% O2 Oxygen 20.9%

The absence of oxygen was a key factor in the beginning of life.

Scientists may never now exactly when and how life originated on earth, but they have several hypothesis based on what they know today.

Based on this information scientists infer that life originated in four steps.

1. Inorganic(nonliving) matter Simple organic molecules

2. Simple organic molecules Polymers(chains of organic molecules)

3. Polymers Protocells

4. Protocells Cells

Inorganic(nonliving) matter Simple organic molecules.

Organic Molecules- A compound that contains carbon and is usually associated with living organisms.

The hypothesis of Chemical Evolution,1924: Alexander Oparin formed the first theory on how organic molecules might have been formed.

He Hypothesized that energy in the UV radiation and lightning stimulated chemical reactions in the ancient atmosphere. These random chemical reactions, occurring over millions of years, produced organic molecules.

Stanley Miller and Harold Urey performed a test on Oparins hypothesis, 1953: They made a model of the ancient atmosphere by mixing gases in a reacting chamber with electrodes simulated the lightning.

After one week, liquid was collected and analyzed, and they found amino acids and other organic molecules had formed!

Miller and Urey showed that Chemical Evolution could have occurred under the conditions modeled by their experiment.

Other scientists have tested the Chemical Evolution hypothesis with different gases and energy sources and have produced not only amino acids but also ATP, DNA, and RNA.

Simple organic molecules (monomers) need to organic into complex organic molecules or chains of monomers called polymers.

Example: Protein polymer is composed of a chain of amino acids. (Complex Molecule) (Simple Molecule)

Two Events must occur for polymers to form:• The monomers must be close enough to react

with one another.• Monomers must chemically bond.

Theories of how this occurred:• Chance meetings in the early seas.• They formed in evaporating puddles of water.• Developed in clay formations.

The formation of the cell membrane, needed to separate internal environment from external environment so chemical reactions of life could occur inside the cell.

Microspheres- Protein and water bubbles, look and behave like cell membranes. Could divide, but could not pass traits to offspring.

At some point in life protocells absorbed nucleic acids (DNA, RNA). Now they could reproduce and transfer genetic information of offspring.

As organic compounds increases in the protocell, this would enable essential chemical reactions and energy production similar to metabolism. It could be truly called a living thing.

The First Cell