Teaching Evolution 4/5 – Timescales

Many people, including students – and probably teachers, too – struggle with the idea that all living things are related to each other. We certainly struggle with the thought that we have close relatives, chimpanzees, who seem to us to be so different. Even when I point out that so much of the similarities are invisible to us, my students can’t cope with the thought that there’s been enough time for natural selection to cause the noticeable differences. The difficulty is that we can’t grasp the time involved.

The Earth is old. I mean, really, really old. And when we say this to kids, they think it means a few thousand years old. A few might start thinking in millions. What we need to do is put the age of the Earth, put the ‘clock’ of evolution, in perspective. I have several ways of doing this, but they’re inspired by one of Richard Dawkins‘ analogies (quote tracked down on a forum on his website).

“Fling your arms wide in an expansive gesture to span all of evolution from its origin at your left fingertip to today at your right fingertip. All the way across your midline to well past your right shoulder, life consists of nothing but bacteria. Many-celled, invertebrate life flowers somewhere around your right elbow. The dinosaurs originate in the middle of your right palm, and go extinct around your last finger joint. The whole story of Homo sapiens and our predecessor Homo erectus is contained in the thickness of one nail-clipping. As for recorded history; as for the Sumerians, the Babylonians, the Jewish patriarchs, the legions of Rome, the Christian Fathers, the dynasties of Pharaohs, the Laws of the Medes and Persians which never change; as for Troy and the Greeks, Helen and Achilles and Agamemnon dead; as for Napoleon and Hitler, the Beatles and the Spice Girls, they and everyone that knew them are blown away in the dust from one light stroke of a nail-file.”
(This version from Unweaving The Rainbow, many similar ones around.)
On the spur of the moment in a lesson, I produced a list of landmark times for one of my classes. Slightly tidied (and corrected, I must admit) it starts in the present day and goes back in larger and larger steps.
now – 2010
60 years ago – 1950CE – post WW2, rationing, no electronics, cars still a rare luxury in the UK.
600 years ago – 1400CE – Middle Ages, the time of knights and castles, peasants and Robin Hood.
6 000 years ago – 4000BCE – the first cities (Ur), before Stonehenge and the Pyramids.
60 000 years ago – humans migrating ‘Out of Africa’ to every continent except Antarctica.
600 000 years ago – Homo Heidelbergensis using tools, weapons, possibly clothes and language.
6 000 000 years ago – common ancestor of humans and chimpanzees.
60 000 000 years ago – dinosaurs RIP, mammals taking over on land.
600 000 000 years ago – the most complex lifeform on Earth was probably a worm.
It might be interesting and/or useful to give these points to students and challenge them to show the timeline using pictures – research lesson anybody? Alternatively produce a powerpoint yourself and use it as a starter or plenary.
You can find some nice animations online, such as the Prehistoric Timeline at the National Geographic website. A few other useful resources will be posted tomorrow but I’ll finish with an Excel sheet (disguised as an Word document) I’ve played with. Type the room you have available into the appropriate box and it will tell you the correct distance from the origin for all kinds of ‘landmarks’. This could be prepared ahead of time, or students could be given the values and asked to attach masking tape signs at the appropriate points on a piece of string (e.g. 4.6m of string equal to 4600 million years would put all human and protohuman history, up to tool use, in the last centimetre).
Activity: timeline saved as docx – once open, you can edit the Excel sheet assuming you have the software.

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