Noticing: Based on the evidence in the geologic record, students were asked to construct a timeline on three adjoining sheets of graph paper. This allowed them to get a sense of scaled geologic time, including the distance between events, as well as the sequence of events.
Things that students noticed were:
The first bacteria were present prior to any oxygen in the atmosphere. Students thought this made sense because it is known that many bacteria are anaerobic (can live in the absence of oxygen).
Photosynthesis is the process by which plants make food. In this process carbon dioxide is taken in by plants and oxygen is released. This event happens before evidence of abundant atmospheric oxygen.
After evidence of abundant atmospheric oxygen, fossil evidence of more complex life forms is observed. Since the majority of life on Earth is dependent on oxygen, this sequence of events seems logical
According to the evidence, life exists in water initially. Prior to any life existing on land, evidence of plant fossils on land are found first. In order for life to be on land, there must be a way of these organisms obtaining energy, which plants would provide.