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Time Scale on a Towel

written by:
Cam Tsujita,
Department of Earth Sciences,
The University of Western Ontario

The vastness of geological time is almost impossible for us to realistically appreciate.  To most of us (especially teachers), one year may seem a very long time.  Ten years is a longer time, but we can still get an inkling of how long a decade is.  A hundred years is very difficult for us to appreciate since most of us don't live that long.  The concept of one thousand years is even more difficult to appreciate.  Now consider one million years - a standard unit of time used by many Earth Scientists.  Can we even begin to appreciate that length of time ?  Regardless, you will hear most Earth Scientists talk casually about intervals of tens or even hundreds of millions of years.  Clearly, at this other end of time perceptions, Earth Scientists find it difficult to think about processes on time scales of days, weeks or decades!  This exercise will give you an idea of the length of time contained in the geological time scale.

Materials Needed For Activity:
One 50-sheet roll of heavy-duty paper towels

Next time you are in the supermarket, look for a 50-sheet roll of heavy-duty paper towels.  Rip off 4 of these sheets to use for another purpose.  You now have 46 sheets.  This is the time line for your geological time scale.  The age of the Earth is estimated to be 4.6 billion (4,600,000,000) years old, so each sheet of towelling will represent one hundred million (100,000,000) years of geological time.  You can then mark in the major events in Earth's history on the paper towel roll, coverting time to the appropriate distance on your time scale.  Since each paper towel brand will have its own sheet length, it is suggested that you use on e of the extra sheets to make a scale for marking the more closely speaced events.  Mark 10 equally spaced divisions on the extra sheet, each defining 10, 000,000 years, then divide these into 1,000,000 year intervals and so forth.  It is also suggested that you mark the most events in succession from youngest to oldest down the roll (this is easiest since much of the information is crowded toward the "present day" end).  The are some major events, based on relative and absolute dating methods.  All dates are highly approximated and are cited in years before present.

0 yrs. - present day
10,000 yrs. - last ice age ends
500,000 yrs. - first modern humans
1,600,000 yrs.- last ice age begins
4,000,000 yrs. - first human-like primates (Australopithecus afarensis)
65,000,000 yrs.- extinction of non-avian dinosaurs
70,000,000 yrs. - Rocky Mountains begin to rise
150,000,000 yrs.- first "true" birds ("avian dinosaurs")
226,000,000 yrs.- first true mammals
240,000,000 yrs. - first non-avian dinosaurs
300,000,000 yrs. - first insects
330,000,000 yrs. - first reptiles
360,000,000 yrs. - first amphibians
365,000,000 yrs. - second uplift of Appalachian mountains
400,000,000 yrs. - first land plants
450,000,000 yrs. - first uplift of Appalachian mountains
500,000,000 yrs. - first true vertebrates (primitive fishes)
600,000,000 yrs. - first animals with skeletons (invertebrates)
3,500,000,000 yrs. earliest record of life (bacteria)
3,960,000,000 yrs. - oldest known rocks on Earth
4,600,000,000 yrs. - birth of the Earth

Once you plot these events on your time scale, you will appreciate both the age of the Earth and the insignificance of modern humans in the context of geological time.  Compare the length of time humans have been on the Earth (500,000 yrs.), relative to that of the non-avian dinosaurs (amost 200,000,000 yrs.).  Can we say that the dinosaurs were unsuccessful animals ?  I don't think so.