IB Biology A2.1 Notes

Whilst it is important to understand the behavior of cells, it is also important to understand where they came from. This starts with understanding the conditions of early Earth that led to their development. It is hypothesized that prebiotic Earth was home to a reducing atmosphere. This means that no oxygen was present, as plants did not exist, and the atmosphere was rich in inorganic molecules such as H_2, H₂S, and NH₃ with CO₂ and CH₄ as the carbon sources.

The physical conditions predicted on prebiotic earth consisted of:

1. Oceans of water due to frequent asteroid bombardment.
2. Ionising radiation from space made worse by the absence of O₃ (ozone) in the atmosphere. 
3. Intense heat.
4. Frequent electrical storms.
5. Volcanic and thermal vent activity.

Prebiotic earth thus provided the conditions needed to produce simple organic molecules such as methane (CH₄) and carbon dioxide (CO₂), which became building blocks of more complex molecules such as amino acids, nucleotides, sugars, and lipids. These polymers may have spontaneously been produced in these conditions that ordinarily would not occur.