I. Geological and Evolutionary Timeline

Earth is approximately 4,600 million years old (equivalent to 4.6 billion years old). The major events of the evolution of life on Earth are summarized in Table 1, and together with the exercise that follows are adopted (with modification), from Barrow 2016. Your instructor might ask you to read the article entitled “Picturing Evolution through Geologic Time” before coming to the lab.

Activity 1: Evolutionary Representation of Timeline on Earth

1. Using string (thread) and a tape measure or a long ruler (see Figure 1), measure a piece of string 4.6 meters long. Lay it flat on the bench. This represents a timeline of Earth’s 4.6 billion year history.

Calculate what each unit of the ruler represents in the number of years. For example:

If 4.6 m = 4.6 billion years, then 1 m = 1 billion years.

1 m = 1 billion years

1 cm = _____ years

1 mm = _____ years

2. Using masking tape, place a thin piece of tape on the string at the appropriate distance to indicate each evolutionary event from Table 1 on the string. On the tape indicate the date and the event. Do this until you have marked all the events on the string. Please note that in order to mark the events to scale as required, you will need to use the conversion factors you calculated in the previous step. For example, if you are marking the origin of the prokaryotes to scale, you need to know how far 3400 million years would be from 4600 million years (the beginning of your timeline). You can solve it using algebra.

[latex]\frac {3400 \text { million}}{4600 \text { million}} = \frac {x}{4.6 \text {m}}[/latex]

You can solve for x algebraically as follows:

[latex]x = \frac {3400 \text { million * } 4.6 \text { m}}{4600 \text { million}}[/latex]

The units “million” cancel, and your final answer is in meters (m).

This tells you how many meters to measure from 0 (the end of your timeline, or the present day). That is the point where you will place the event “prokaryotes.” Calculate the other events in Table 1 in a similar manner.

3. Answer the following questions.

a. What patterns if any did you notice in the timeline? In other words, what did you notice or what surprised or interested you about the spacing of the events?

b. What proportion (in %) of Earth’s life history does each even represent? Complete your work in a table like Table 2 below. Show your calculations.