Activity 1: Geologic Time Line

THREADS OF LIFE

Summary:

This activity takes 4.65 billion-years of Earth history and compresses it into a scale of 100 meters. Students use pre-measured string to represent the existence span for various groups of plants and animals.

Instructional Method: Activity

Goal: To show the depth of earth history and how and when various fossil life originated, evolved and/or went extinct.

Objectives: Students will be able to:

• Visualize how much time and life has passed on Earth.
• Locate mass extinction events.
• Observe how rarely an extinction event wipes out an entire order or family of life and how the rapid radiation of the surviving species quickly fills the gap.
• Discuss various measures of life form success.
• Observe species extinctions and time variations. For example, dinosaurs and cavemen did not live at the same time.

Time:

Preparation: 60 min.
Activity: 30 min.
Discussion: 20 min.

Materials Needed:

• Lots of string
• 100 meter measuring tape and/or a football field

Vocabulary:

amoeba	dinosaur	million
amphibian	endosymbiosis	mitochondria
arthropod	era (geologic)	Paleozoic
billion	evolve	photosynthesis
Cenozoic	extinct	Precambrian
chloroplasts	flatulence	reptiles
conifer	mammals	trilobite
cyanobacteria	Mesozoic
deciduous	meteorite

Background:

Life is what makes Earth unique in the known universe. Many different kinds of living things have come and gone in the last 3 billion years.

During the Precambrian Era (4.6 billion to 600 million years ago), approximately 3.6 billion years ago, colonies of single cell cyanobacteria appeared as the first life forms recorded by the fossil record. For nearly 2 billion years, they alone inhabited the barren oceans underneath an oxygen free atmosphere. They formed algal mats and mushroom shaped nodules called stromatolites. Being photosynthetic, they took carbon dioxide out of the atmosphere and excreted oxygen as a waste product, thus oxygenating the world's oceans and atmosphere. Ironically it was their success that almost caused their extinction. Their primitive cell membranes decayed when exposed to free oxygen molecules. In short our planet's first and most successful life forms almost drove themselves to extinction - attacked by their own flatulence. Oxygen richness led to more complex single celled organisms like amoebas.

About 1.5 billion years ago, a momentous event occurred. Instead of digesting the cyanobacteria they had engulfed, amoebas allowed them to live on within the protection of their stronger cell membranes. In exchange for protection, these cyanobacteria supplied photosynthetic energy, becoming the first cellular chloroplasts and laying the ground work for algae and later plants. This relationship, called endosymbiosis, created the foundation for all subsequent food chains, thus allowing for the diversity of life our planet now holds.

Multi-cellular life evolved approximately 800 million years ago (mya), and by the beginning of the Paleozoic period (600 - 265 mya), there was an explosion of life where sea creatures like corals, trilobites, primitive fish and eventually sharks abounded. Life remained confined in the oceans until primitive plants evolved. Arthropods like centipedes, spiders and scorpions advanced on to the land about 375 mya.

Later in the Paleozoic, amphibians evolved from lungfish that moved on to land. Primitive swamp-forests covered all landmasses. The unusually high amount of oxygen created by these global forests made big "bugs" possible. Gigantic arthropods including dragonflies the size of hawks, cockroaches the size of rats, and centipedes 6 ft. (3m) long eventually lost out to amphibians and their descendants. By the end of the Paleozoic, 270 mya, conifer trees evolved, and the basic forms of vertebrates were well established. Early mammal-like creatures such as the sail-backed Dimetrodon and the wolf-like Lycaenops dominated over large turtle-like herbivores and small lizard-like reptiles.

The most devastating extinction the planet has ever known (the cause of which is still unknown) marks the end of Paleozoic and the beginning of the Mesozoic (265 - 65 mya). Almost all early sea creatures including trilobites went extinct, and big changes occurred on land. Dinosaurs quickly took over, sending early mammals into relative obscurity in the form of small nocturnal tree-dwelling creatures. For 200 million years dinosaurs and reptiles reigned supreme, controlling not only the land, but also the seas and the air.

A common misconception is that all dinosaurs of the Mesozoic lived together. Actually most types lived for only a few million years, either going extinct or evolving into new forms (see the stratigraphy activity for charts showing what animals coexisted). The first birds evolved in the middle of this era at about 185 mya. Most of the modern plant life we recognize originated in this era. Deciduous trees arose early in the Mesozoic, and flowering plants became widely spread at the close of the Mesozoic.

The Mesozoic ended abruptly 65 mya with an extinction possibly caused by the impact of a large meteorite. This disaster caused all land animals larger than 40 lbs. (18 kg), that weren't crocodiles, to go extinct. In the following geologic era known as the Cenozoic (65 mya - present), mammals descended from their hiding places in the trees to fill the void left by the dinosaurs and reptiles. Much of the mammals' success came from capitalizing on grass which first appeared about 30 million years ago. Grass allowed land mammals to attain huge size, some even rivaling the dinosaurs before them. In the seas, mammals that evolved from primitive cats became whales, ultimately leading to today's blue whale -- the heaviest animal to ever live. But, by the end of the ice age (15,000 years ago), all but a few of the giant land mammals went extinct. Birds, thought to be cousins of the dinosaurs, also diversified in the Cenozoic, but eventually they had to share the skies with bats, the mammalian flyers. Human-like creatures, the most notorious mammal of all, have only been on the planet for 2 million years. However, we have had a greater impact than any other life form in earth history, with the possible exception of the cyanobacteria . Hopefully our success won't ultimately lead to our own downfall as with the cyanobacteria. . . Only time will tell.

Instructional Procedures:

1. Assign each student a living thing. Have them research the range of years that their species existed. The creatures from the stratigraphy activity could be used. Make sure to include some microorganisms and humans.
2. Have students figure out how long their assigned species existed in relationship to the 4.65 billion years that the Earth has existed.
3. If the age of the Earth is represented by 100 meters, have students figure out how long to make a string to represent the existence span of their creature.
4. Have students cut string in the appropriate lengths.
5. Select a location large enough to accommodate the activity - an open area 100 meters long. A football field would be ideal. Lay out the measuring tape. Explain how the 100 meters represents the whole of Earth's existence. Teach students how to read the distances on the tape and convert to years.
6. Starting at the Precambrian end and working forward in time, lay out each life form's time line. Have students place one end of the string on the ground where their organism began and the other end where the organism went extinct, or to the present day if it still survives. Direct students to spread out their strings so that they don't become tangled and laid so closely together that they become confusing.
7. Discuss the completed time line.

Discussion:

Encourage students to locate points of mass extinction among the strings. Discuss why some extinctions might be more obvious than others. Lead them to the understanding that extinctions mean both mass die off and also a radiation of new life. Discuss the concept of success and various ways and measures of success. Ask open ended question like: Does an organism have to big, powerful, intelligent to be successful? Ask the students if they could use a time machine, what part of the timeline would they most want to visit and why? Discuss the number of mass extinctions survived, total time spent on earth vs. body size and complexity, and behavioral sophistication.

Variation:

Using yards instead of meters is a plausible option and makes sense if using a football field. However what might be gained in familiarity would require converting decimals to inches. Using multiple 100 meter / yard measuring tapes would allow students to work more efficiently. Thought should be given in assigning creatures, so that no particular geologic era is underrepresented.

Extension:

Introduce various subdivisions of each Geologic Era and assign students to research and produce a written or oral report on one of the time periods.

Included National Parks and other sites:

Agate Fossil Beds National Monument
Alibates Flint Quarries National Monument
Dinosaur National Monument
Florissant Fossil Beds National Monument
Fossil Butte National Monument
Grand Staircase-Escalante National Monument
Hagerman Fossil Beds National Monument
John Day Fossil Bed National Monument
Petrified Forest National Park

Photos:

Geologic Time Scale Chart
Early Earth
trilobite

Utah Science Core:

4th Grade Standard 4 Objective 1,2

 

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