Modeling the Geologic Time line and the Development of ...



Pictorial Model of the Geologic Time line and the Development of Life on Earth

Background Information

The geological time scale (table 23.1) pertains to the history of the earth from its formation 4 to 4.5 billion years ago to the present. The ages of rocks can be measured in years by analyzing naturally occurring radioactive elements found in certain rocks and minerals in minute quantities. Formerly, geologists depended on a relative dating system; that is, they reasoned that any given stratum (layer of sediment) is younger than the stratum of the earth's crust just beneath it.

Because certain fossils are associated with particular strata, geologists are able to relate various strata around the world. Fossils are the remains and traces of past life or any other direct evidences of past life. By the 1860s, fossil-containing rocks in western Europe were divided into three great eras: Paleozoic (ancient life), Mesozoic (middle life), and Cenozoic (recent life). Each era is divided into periods, and periods, in turn, are divided into epochs. The first period of the Paleozoic is called the Cambrian, and the time before the Cambrian period is called the Precambrian. The oldest fossils have been found date from the Precambrian. For reasons that are still being explored, the fossil record improves dramatically starting with the Cambrian period.

Notice in table 23.1 that divisions of the geological time scale generally tend to become increasingly shorter: For example, the Cenozoic era is much shorter than the Paleozoic era, and the Quaternary period is much shorter than the Tertiary period. Notice also that time is measured as "millions of years ago," and therefore, larger numbers represent an earlier time than smaller numbers.

The earliest traces of life suggest the presence of microorganisms about 3.5 billion years ago during what scientists call the Precambrian era. The first cells with nuclei appeared about 1.5 billion years ago. These evolved into simple forms of life that gave rise to more complex forms. Land plants, amphibians, and insects came into existence between 435 million and 225 million years ago during what scientists refer to as the Paleozoic era. Dinosaurs dominated the Mesozoic era, which began about 225 million years ago. The most recent era, titled the Cenozoic, began about 65 million years ago. It was not until the last several million years of this era that human beings appeared on earth.

Objective:

• To construct a pictorial geological time model in scale to the real time line.

• To construct a pictorial time line for the appearance of organisms in the geological time scale.

• To study the history of different living organisms through images.

Materials, Facilities and Resources:

writing utensils

a broad selection of materials for construction (e.g., paper, calendars in various formats, rolls of adding machine paper, clock faces, etc.).

reference materials (may include time lines, calendars, etc.)

measuring devices (rulers, meter sticks, tape measures, etc.)

Resource:

Note: The timelines are intended to show the dominant life forms during the geological eras not replacement, they do not include transitions of different organisms.

Procedures:

1. Working in groups, the students will develop a pictorial model of the Earth's geologic time scale. The scale should model the real time of planet earth. Students can choose to construct a linear geological time line or compare the geologic time scale to a year, month or day on earth, etc. Be creative! Using “table 23.1”, plot the different divisions: eras and periods on your time scale. Label the divisions and the number of years ago it occurred. Don’t forget to include a key for your scale. Example: 1 cm = 1 million years.

2. Plot the major evolutionary events of each geological period. Include lots of images ( pictures or drawings) of various events. Use the given “table 23.1”, text (17-2) and other sources in the construction of the time scale.

Examples of Divisions and Events in Earth’s History:

|Divisions: Eras and Periods | |

|Events: | |

|Formation of earth |History and Diversity of plants |

|First Prokaryotic cells |History and Diversity of animals |

|First Eukaryotic cells |First Primates |

|Multicellular organisms appear |First Hominids appear |

|Algae flourish |First humans appear |

| |Formation of Pangaea- 225 mya |

| |Breaking Apart of Pangaea |

| |Continents reach present position |

Questions to consider in the construction of the time scale:

(You do not need to answer these questions.)

1. In which era did dinosaurs exist or begin to exist? Mammals?

2. Which lived on Earth the longer time, dinosaurs or mammals?

3. During which era and period did the first vascular plants appear? How many million years ago was this?

4. Angiosperm (flowering plant) diversity occurred during which era and period? How many million years ago was this?

5. During what period did the trilobites appear? When did they become extinct?

6. During what period did the insects first appear? How many million years ago was this?

7. During what period did the vertebrates first appear? How many million years ago was this?

8. During what period were the cycads most abundant?

9. What types of animals were also prevalent at this time?

10. During what period did the angiosperms (flowering plants) evolve? How do you know they are the most abundant plants today?

11. What is the age of human civilization?

Analysis and Interpretation:

(Answer these questions individually.)

1. How are years represented on your model?

2. Which era is the longest? The shortest?

3. How does your model help you visualize the rate of evolutionary change in different groups of organisms?

4. What group of organisms occupied most of the Earth's history?

5. What factors may have triggered the explosion of animal and plant diversity during the Paleozoic era?

6. How does the fossil record provide evidence for evolution?

7. When did humans first appear and how long have human existed on earth?

8. Which two cellular processes are considered to be the major driving forces leading to the explosive evolution and diversity of living organisms throughout the history of the Earth?

Choices: DNA replication, anaerobic respiration, aerobic respiration, mitosis and photosynthesis.

9. Using approximate geologic times and common names; briefly summarize the major events occurring in organisms' evolution and diversity from the Cambrian period through the Quaternary period of the Earth's history.

Adapted from Utah State Office of Education.

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