Thinking About Life in Geological Time Scales:

When did all the cool and important stuff in the history of life happen?

Author: Joseph Spagna
(Modified from What Came First - http://www.ucmp.berkeley.edu/fosrec/ScotchmoorFirst.html)

Objective:

  1. Students will create a large (classroom-sized) timeline showing the history of life on Earth for the last 5 billion years.

  2. Students will be able to identify the events that are relevant to their taxonomic projects (the origins and important developments in their groups' study taxa)

Grade span: 9-12

Introduction:
Lecturing / explaining geological time just using big numbers is not the most effective way to help students understand the overall arc of the history of life, nor the time-scales involved. Instead, this lesson takes a more 'kinematic' approach, by having the individual students make, and change, hypotheses about when the important events in the history of life have taken place, and physically moving markers representing these events, until the entire class has an accurate timeline in their classroom.

Materials:

  • Giant roll of white, not-too-flimsy butcher paper, at least 10m total paper length.

  • ~ 40 Big Post-its (the ones about the size of a reporters notepad-- ~ 3" by 6"), multiple colors will provide more contrast, particularly between events that may happen very close together on the timeline (eg chimp-human split and origin of modern humans).

  • Big black felt marker

  • Scotch tape

Teacher Prep time: 1-2 hours, to create the "Event Post Its"
Teacher needs to make Big Post its (ones that can be read from a distance of 5-10 feet) with the names of the Big Events (see list below). Teacher should also review the list of events to make sure they are all familiar or at least make sense.

Procedure:

Motivation-- 5 minutes:
Ask a question that students might think is controversial, but is pretty settled scientifically-- eg. has any human being ever seen a live dinosaur? Guide students to answer (NO) but then focus on -how- we know this: there is actually a timeline that scientists are always working on when studying the history of life. Show students blank time line around classroom and explain that we are going to build our own class version of the timeline.

Building the timeline:

Step 1: The events. 5-10 minutes.

Pass out the Big Event Post-its to the students. Explain that some of them are simple to understand, (first modern human) but if you don't know what yours means, it's not a problem but YOU NEED TO ASK! Answer their questions in whole-class discussion format, so that all students hear what they are (eg, most 9th graders won't know what "glaciation" is-- you're going to explain it means, coming of glaciers, or Ice Ages.

Step 2: Initial hypotheses. 10 minutes

Students now are to get up, walk around, and look at the timeline and decide where they think their "Big Event" goes. Then stick it on there. It is ok to discuss with other students and look where they are putting their events, but each student should choose on their own. When students are done look at where things are: they are likely to be much more spread around the room than they should be (that's one of the secrets of the lesson-- the good stuff is crowded in the last 500M years, so only ~ 20% of the butcher paper will have 90% of the Big Events).

Teacher help: Moving, or adding some key events (you can hold out a few that make a big difference if you think this will help) , with an explanation for each thing you say, and how scientists know this (fossils? tree rings? ice cores?).

Step 3: Rethought Hypotheses. 10 min.

If something makes you think your hypothesis needs "updating" based on teacher provided data, then go ahead and move your Post-it! (most *will* need to move theirs). During this portion, you will actively need to help students -think- about the logic of things... eg, flowering plants could not have evolved before multicelled life! Apes should have evolved before the chimp-human split, etc. It should start looking more reasonable if not "right" by now.

Step 4: Fixing it up... Remainder of class ~15 min

Now is where we make the final changes. Have each student write down (on a piece of notebook paper) where there event was after step 3. Now use your key to correct any mistakes (there will be many, at least small ones) and have the students figure out how "off" their 2nd hypothesis was. You can give a prize for the "closest" person, or the one with the smallest differential. While doing this, explain how scientists know these things (to the extent you know) and why they are considered Big Events. Let students stand back and check things out: ask: what patterns do we see?

Step 5: (for RHS students) Find your group (2 minutes)

Since RHS students are doing projects studying particular taxa, they should find the origin of their taxon and any other dates that might be important in the history of their group.

Reflection:

This is a fun way to visualize the geological time scale for natural history, and leaves a really cool decoration around the class as long as the teacher is willing to leave it up...

Important Events in Geologic Time
Big Event # of Years Ago
Human History Begins ~5,000
Breakup of Pangaea 200 million
Camels 50 million
Ants 80 million
Grasses 22 million
Homo Sapiens 500,000
Primitive Whales 54 million
Chimpanzee-Human split 6 million
"Lucy" 3.2 million
Glacial cycles began 1.6 million
First Apes 33 million
Triceratops 70 million
Dinosaur extinction 65 million
First flowering plants 140 million
Trilobites go extinct 253 million
Pangaea forms 290 million
First Mammals 220 million
Largest extinction 248 Million
Archaeopteryx 150 million
Earthworms 200 million
Ferns 400 million
Amphibians 395 million
First land plants 440 million
Sharks 390 million
Spiders 420 million
Winged insects 330 million
First Insects 380 million
First jawed fish 400 million
Jellyfish 540 million
First fungi 550 million
Green algae 1 Billion
First Eukaryote 1.8 Billion
 
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