GEOLOGIC TIME -- contributed by Nancy McHone

What is a long time?

Teacher Sheet

Background

The concept of geologic time is often difficult for students to comprehend.  To a thirteen-year-old, ten years is a long time.  Millions or billions of years is just another long time, longer than ten years, but how much longer is meaningless.  To give students a feeling for geologic time, it needs to be seen relative to a time they understand.  For that purpose, a timeline can be constructed.  This exercise is designed to show the entire history of the Earth and of Connecticut in a single timeline.  A football field or some other long, straight space can be used to construct the time line.

Procedure

Give the students the list of ages of geologic events.  Assign each of them an event.  Ask them to make signs on pieces of poster board for their event.  Then glue sticks to the two sides of the boards so that the tops of the sticks are even with the tops of the signs.  If you want the signs to last long enough for the rest of the school to see the timeline, cover the signs with plastic bags taped in place.  Using books as references, they should then make a poster depicting what a landscape might have looked like at that time. The finished posters can be posted around the room in chronological order, to create a scenic time line.

Next, have three students measure the length of the field or other space to be used for the timeline.  If there is no long field, or the weather is too bad, a long hallway inside the school can be used, but some of the more recent events will be too close together to include all of them.  Calculate the average to use as the length.  They can calculate the location of the different events along the timeline, then place their signs in the appropriate places.

What is a long time?

Student Sheet

Background

The Earth is very old – 4,600,000,000 years old.  That is 4.6 billion years.  But a billion years is difficult to talk about and even more difficult to imagine.  Because of the long time periods involved when talking about events in the far past, geologists talk in geologic time.  Geologic time means a veeery long time.  To try to picture what a billion years is like, or even a million years, you can make a timeline.  Along a timeline you can see when events in the Earth’s geologic history happened in relation to other events.

Table 1. Important Dates in CT geologic history

MYA = million years ago

4600 MYA  Beginning of Earth

3600 MYA  Blue-green algae and stromatolites

2500 MYA  Primitive aquatic plants

750 MYA  Assembly of supercontinent, called "Rodinia"

630 MYA  Rifting of Rodinia, begin to open Iapetus Ocean; proto-North American
terrane in Connecticut is along shore with offshore reefs

670 MYA  Oldest fossil evidence of marine worms and jellyfish

570 MYA  Trilobites dominant

550 MYA  Iapetus Ocean begins to close, island arc begins to form offshore of Connecticut,
behind subduction zone

500 MYA  First fish

435 MYA  Early plants & animals on land

370 MYA  First amphibians

360 MYA  Sharks & large primitive trees

330 MYA  Fern forests, abundant insects, first reptiles

250 MYA  Pangea complete. Some of Iapetos ocean floor and island arc added to Connecticut between
proto-North America and  Avalonia.  Largest known mass extinction (90% of all species disappear).

240 MYA  Coniferous trees abundant

228 MYA  First dinosaurs (about the size of cats)

205 MYA  First birds & mammals, abundant dinosaurs

200 MYA  Basalts begin erupting in central Connecticut as Pangea is breaking up and Atlantic
Ocean will soon begin to form.  Large mass extinction (50-60% of all species).

140 MYA  Flowering plants

65 MYA  Mass extinction.  Comet or meteor collides with the Earth, and most animals on land and sea weighing more that 3-kg perish.  Or the extinctions may have been caused by large volcanic eruptions, which darkened the skies for years, cooling the climate suddenly.  End of dinosaurs.

4.5 MYA  First humans appear on Earth

26,000 years ago Last glacier begins to cover Connecticut

15,000 years ago Glacier completely gone from Connecticut

Procedure

1. To see how long 1 billion seconds is, figure out how many years equal 1 billion seconds.
Begin by calculating the number of seconds in a year = _____________.  Then divide 1
billion seconds by that number.  The number of years = _________________.

2. Make a sign with the age of a geologic event.  At the top of the sign put the number of years ago the event happened, such as 240 Million Years Ago.  Below that, write the event – Coniferous Trees Abundant.

3. Using classroom books as references, make a poster of what the scenery might have looked like at the time of your event.  Print the time on the bottom of the poster, as you printed it on your sign.  These can then be placed around the classroom walls, in time order, as a pictorial timeline.

4. Three students from the class should measure the length of the space where a timeline will be constructed.  The length is _______ meters.

5. Multiply the length in meters by the number of centimeters in a meter.  The length in centimeters is _______ centimeters.

6. To determine the number of centimeters needed to represent 1 million years, divide the length of the timeline in centimeters by the age of the Earth (in millions of years) = ___________ cm/million years.

7. Age of your event = ________ million years.  How many centimeters on the timeline is this?

___________ cm or _________ meters

8. Measure the distance along the timeline representing your event, starting from the present end.  Place your sign there.

9. Divide the number centimeters representing 1 million years by 1 million to find out what part of a centimeter represents 1 year = _______ cm.  Now multiply that number by your age. Your age is represented by _____ cm.   In relation to the history of the Earth, the number of years since you were born is too small to represent on the timeline.  Geologic history is veeeery long!