A2.1 The origin of cells

Introduction (Are Vents responsible for life)

What makes you say that? Discussion.

  • Prompt question: What evidence is there that hydrothermal vents were the location where life may have begun?
  • Speaker makes a statement expressing a thought
  • The person on their immediate right responds by saying ´What makes you say that´
  • The speaker is given a chance to respond

A2.1.1 Conditions on early Earth and the pre-biotic formation of carbon compounds

Lesson (30 minutes)

Objective: Compare conditions of pre-biotic Earth with modern day Earth and explain changes.


  • Pre- biotic period. A time period of Earth´s history before any living organisms existed.
  • Methane (CH4), Carbon dioxide (CO2) and Oxygen (O2) are atmospheric gases.
  • UV light. UV light forms part of solar radiation, a form of radiation with dangerously high energy content.
  • Stratosphere. A layer of the Earths atmosphere that contains high levels of the gas ozone (O3), hence known as the ozone layer.
  • Building blocks of life. Certain organic compounds that are found in high levels in the cells of living organisms. Amino acids, carboxylic acids, nitrogenous bases and carboxylic acids.

During the Pre-biotic period, conditions on Earth were less suitable for life. This is mostly because the concentration of oxygen was too low to sustain many living organisms, and the concentration of carbon dioxide was so high that the greenhouse effect was much greater than it is today, warming the Earth´s atmosphere to higher levels than today. There was almost no ozone layer in the stratosphere, and therefore very little protection from UV rays which would would have been dangerous to life forms, or at least caused a high rate of genetic mutations.

When the first algae and certain bacteria evolved on Earth, they began the process of photosynthesis. Plants continued this process, accelerated by the evolution of trees. This had a major impact the concentration of oxygen, which rose to form 1/5 of the Earth´s atmosphere, atmospheric carbon dioxide plunged to around 0.05% although this is currently rising. 

As UV light interacted with oxygen, the compound ozone was created, in sufficient quantities to form the ozone layer. This reduced the amount of UV light reaching the Earth´s surface.

It is thought that in order for life to have evolved, some of organic compounds in life needed to have formed first. This included amino acids, carboxylic acids, nitrogenous bases and carboxylic acids.



Activity: Proxima B is our closest exoplanet (a planet but from another solar system). Take a look at it here https://exoplanets.nasa.gov/resources/2211/proxima-b-3d-model/

Discuss how you would predict the atmospheric levels of oxygen, carbon dioxide, and ozone to compare with modern day Earth. Justify your arguments.

A.2.1.2 Cells as the smallest units of self-sustaining life

Lesson (20 minutes)

Objective: Understand that