A2.1.1: Conditions only early Earth and pre-biotic formation of carbon compounds

Early Earth (4.6 - 4 billion years ago) had

different conditions.

The different conditions are significant because it made it easier for

carbon compounds (organic molecules) to form without life. 

The pre-biotic environment could

support chemical reactions that built up organic molecules from simple starting materials. 

Prebiotic

before life 

Key ingredients for Prebiotic Chemistry: 

Carbon Containing Gases, Lots of Energy, liquid Water and little free oxygen

Carbon Containing Gases in the

atmosphere containing Carbon and Hydrogen 

Lots of Energy

(UV Radiation, Lighting, Heat from volcanism) 

Liquid Water

(Oceans for concentrating, dissolving and reacting molecules) 

Very little free oxygen

(So new organic molecules were less likely destroyed) 

Prebiotic Synthesi

Abiotic chemistry formation of organic (carbon based) 

•  Molecules before cells existed. 

 

Modern Earth's Atmosphere is oxidizing

(contains Oxygen) and is protected by an ozone layer

Early Earth had: 

• Nearly no free oxygen 

• No Ozone Layer 

• More reactive gases by volcanic outgassing and impacted by meteorites 

 

• Nearly no

• free oxygen 

• No

Ozone Layer 

• More reactive gases by

volcanic outgassing and impacted by meteorites 

Context: Oxidation

Reacting involving oxygen that can break down or destroy many organic molecules

Free Oxygen:

Oxygen in the atmosphere available to react 

Ozone Layer is made of:  

Ozone, O₃

Low Oxygen means

low oxidation so fragile organic molecules are not rapidly broken down

The Ozone Layer absorbs the

Sun’s radiation reducing UV reaching the surface

Activation Energy 

Many reactions for carbon molecules needed a push of energy called activation energy. 

 

Prebiotic Earth had multiple energy sources: 

UV, Lighting, Heat, Impact Energy

UV Radiaiton

• • Intense from no ozone layer 

Lighting

• • Electrical Energy from storms 

Heat from

volcanism and potentially hydrothermal vents 

Impact Energy  from

frequent meteorite bombardment 

Activation Energy

Minimal energy required to start a chemical reaction 

Eg Activation Energy: UV photons provide enough energy to

break bonds in simple gases, allowing atoms to recombine into molecules like aldehyde and carboxylic acids. 

No Ozone Layer: 

Early Earth had no oxygen which is part of the Ozone Layer, therefore nothing absorbed the UV. 

More UV:  Break chemical bonds in

atmospheric gases 

More UV:

Creative Reactivity intermediates to

form new carbon compounds 

More UV:

Provide activation energy for

 

reactions that are unlikely under modern surface conditions. 

UV can also break down 

complex molecules therefore scientists think oceans, rock pores, ice and hydrothermal vent environments assisted the protected the molecules. 

UV Stronger:

Low Oxygen and No Ozone Layer 

Atmosphere Gas Main source:  

Volcanic Outgassing with contributions from impacts

With Early Earth

Simple Carbon-Based Molecules could form from smaller molecules. 

Spontaneous (in context) =

compounds can form under the right natural conditions, no driving force 

 

 

Examples of Spontaneous Energy

• Formaldehyde – simple organic molecule 

• Aldehydes 

• Carboxylic Acids 

Why formation was feasible then 

High Energy Inputs (UV, lightening) drove reactions forward 

Low Oxygen reduced destruction by oxidation 

No ozone allowed UV driven reactions near the surface 

feasible formation: High Energy Inputs

(UV, lightening) drove reactions forwarf

feasible formation: Low Oxygen

reduced destruction by oxidation 

feasible formation: No ozone allowed

UV driven reactions near the surface 

Organic molecules contain carbon (often with hydrogen, oxygen and nitrogen) formed

 

abiotically in pre-biotic chemistry. 

Reactions needed energy and early earth had more

natural energy sources reaching reactive gases and water. 

A way to test prebiotic synthesis:   

stimulate an early atmosphere plus an energy source, then check whether organic molecules form.

Core Idea of stimulation:

recreate plausible early Earth like conditions in a controlled system and see what chemistry occurs without any living organism involved. 

 

General Set Up 

• Close system with water (to model ocean evaporation and condensation) 

• A mixture of gases (models of early atmosphere) 

• An energy source like electrical sparks (to model lighting) 

• A trap/collector where products accumulate 

 

• By circulating the gases and water through the system while adding energy, any newly formed compounds can be concentrated in the collector for later analysis. 

 

• Experiment does not prove life formed this way, supports the claim that organic molecules can form abiotically under plausible early-Earth-like conditions 

 

• • The system can collect a variety of organic molecules. 

Ozone Layer 

Atmospheric Layer