Published March 2013

Updated July 2014

www.BioInteractive.org Page 1 of 4

WORKSHEET

TEACHER MATERIALS

FOLLOWING THE TRAIL OF EVIDENCE

OVERVIEW

This worksheet supports the HHMI short film The D ay the Mesozoic Died. As students watch the film, they will write down

the evidence that led to the discovery that an asteroid struck Earth about 66 million years ago, causing a mass extinction.

(Note: The film states that the mass extinction occurred 65 million years ago; that date was recently revised to 66 million

years ago. Refer to the In-Depth Film Guide for more information.)

KEY CONCEPTS AND LEARN ING OBJECTIVES

• Earth’s 4.6-billion-year geological and biological history is deduced from the analysis of fossils, rocks, and

chemical signatures found in sediments worldwide. The layered evidence reveals a pattern of change varying in

tempo.

• Catastrophes have played an important role in evolutionary history. The mass extinctions that have occurred in

the past 550 million years are examples of catastrophic change.

Students will be able to:

• understand the relationship between the geological time scale and the layered pattern of exposed rocks in the

landscape—specifically, that deeper layers are older than layers closer to Earth’s surface.

• identify the evidence that the K-T boundary marks a mass extinction event that coincides with an asteroid

striking Earth 66 million years ago.

• gain an appreciation for the scientific process, which consists of asking questions, making observations,

formulating hypotheses, and gathering and evaluating evidence.

• understand that scientists draw conclusions based on multiple lines of evidence and hypotheses from a range of

scientific disciplines.

• appreciate that in the earth science field, scientists don’t typically conduct experiments to test hypotheses;

instead, they gather evidence to either confirm or refute hypotheses.

CURRICULUM CONNECTIONS

Curriculum

Standards

NGSS (April 2013)

MS-PS3.C, MS-LS2.C, MS-LS4.A, MS-LS4.C, MS-ESS1.C, MS-ESS2.A, HS-LS2.B, HS-LS2.C, HS-

LS4.C, HS-LS4.D, HS-ESS1.C, HS-ESS2.A, HS-ESS2.E, HS-PS1.C,

Common Core (2010)

CCSS.ELA-Literacy.RST.6-8.1, CCSS.ELA-Literacy.RST.6-8.2, CCSS.ELA-Literacy.RST.6-8.4,

CCSS.ELA-Literacy.RST.6-8.8, CCSS.ELA-Literacy.RST.9-12.1,CCSS.ELA-Literacy.RST.9-12.2,

CCSS.ELA-Literacy.RST.9-12.4, CCSS.ELA-Literacy.RST.9-12.8

AP Biology (2012-13)

4.B.4, 1.C.1, SP5

IB Biology (2009)

5.1, 5.4.8, D.2.7, D.2.9, D.1.3, G.2.6, G.2.7

KEY TERMS

evidence, hypothesis, theory, Cretaceous, Tertiary, iridium, asteroid, meteorite, supernova, foraminifera, pollen, spores,

extinction, fossil, sediment

TIME REQUIREMENT

This activity requires two 50-minute class periods.

SUGGESTED AUDIENCE

This activity is appropriate for middle school earth and life sciences and high school biology, earth science, chemistry,

and physics (all levels including AP and IB).

The Day the Mesozoic Died Worksheet Answers, Exercises of Earth Sciences

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TEACHER MATERIALS

FOLLOWING THE TRAIL OF EVIDENCE

OVERVIEW

This worksheet supports the HHMI short film The Day the Mesozoic Died. As students watch the film, they will write down

the evidence that led to the discovery that an asteroid struck Earth about 66 million years ago, causing a mass extinction.

(Note: The film states that the mass extinction occurred 65 million years ago; that date was recently revised to 66 million

years ago. Refer to the In-Depth Film Guide for more information.)

KEY CONCEPTS AND LEARNING OBJECTIVES

chemical signatures found in sediments worldwide. The layered evidence reveals a pattern of change varying in

tempo.

the past 550 million years are examples of catastrophic change.

Students will be able to:

landscape—specifically, that deeper layers are older than layers closer to Earth’s surface.

striking Earth 66 million years ago.

formulating hypotheses, and gathering and evaluating evidence.

scientific disciplines.

instead, they gather evidence to either confirm or refute hypotheses.

CURRICULUM CONNECTIONS

KEY TERMS

evidence, hypothesis, theory, Cretaceous, Tertiary, iridium, asteroid, meteorite, supernova, foraminifera, pollen, spores,

extinction, fossil, sediment

TIME REQUIREMENT

This activity requires two 50-minute class periods.

SUGGESTED AUDIENCE

This activity is appropriate for middle school earth and life sciences and high school biology, earth science, chemistry,

and physics (all levels including AP and IB).

PRIOR KNOWLEDGE

Students should be familiar with hypothesis testing and the difference between a fact and an opinion. They should also

know what a fossil is and understand that older fossils are found in deeper rock layers than younger fossils. They should

be aware of Earth’s geological time scale and its relationship to the relative timing of past events.

MATERIALS

Students will need the student version of this activity. Note that there are two versions of the student handout, one with

extra support for taking notes.

TEACHING TIPS

of Geology and Biology,” available at

http://www.hhmi.org/biointeractive/posters/2012%20Changing%20Planet.jpg). Point out the Mesozoic era and

the Cretaceous period. Explain that the Mesozoic is often referred to as the Age of Reptiles, including dinosaurs.

more guidance on taking notes. Explain that as they watch each act of the film, they should be paying attention

to the key scientific evidence uncovered by the scientists featured in the film about what led to the extinction of

the dinosaurs and many other species at the end of the Cretaceous period.

in that act and what the evidence means in the table provided in their worksheet. To give students a better idea

of what they should write down, the evidence presented at the beginning of the film has already been entered

in the worksheet. Spend a couple of minutes reviewing that evidence.

of study—on scrap paper as they watch the film. These notes will serve as reminders when working in small

groups at the end of each act.

pieces of evidence they recorded. Ask the class to determine whether these examples represent a scientific fact

or an opinion.

hypothesis.

ANSWER KEY

(This is an example of a completed table. Students’ responses will vary.)

EVIDENCE PRESENTED WHAT THE EVIDENCE SUGGESTS

QUESTIONS

1. What piece of evidence initially convinced Dr. Alvarez that a mass extinction had occurred at the K-T boundary?

There were many different foram fossils below the boundary between the Cretaceous and Tertiary periods and

fewer above the boundary, which means that the boundary marks the time of the mass extinction.

2. What was the first clue that an asteroid had struck Earth at around the same time as the mass extinction?

They found a high concentration of iridium, an element rare in Earth’s crust but abundant in asteroids, at the

boundary between the Cretaceous and Tertiary periods.

3. What additional observations and findings supported the asteroid-impact hypothesis?

Scientists have found glass spherules, shocked quartz, and tektites in the K-T layer. These findings are consistent

with a collision or explosion that generated an immense amount of heat and high-energy shock waves. Near the

Gulf of Mexico, scientists have found tsunami deposits. Scientists have found a 200-km-diameter crater in the

Yucatán peninsula that matches the age and predicted size of the asteroid.

4. Which piece of evidence definitely showed that an asteroid had struck Earth? Explain your answer.

The crater at Chicxulub was the smoking gun. Finding a crater that matched the age and size of the asteroid

provided direct evidence for the impact. All the other evidence before was indirect.

5. How does the asteroid-impact hypothesis explain the extinction of the dinosaurs and other species?

A strike by a 10-km asteroid would have caused tons of dust and debris to be blown into the atmosphere,

blocking the sun for many years. Photosynthesis would have stopped, resulting in the death of plants and

eventually animals.

6. Provide two or more examples from the film that illustrate how scientists use multiple lines of evidence and a range of

disciplines to draw conclusions.