Dissecting “Battle of the Americas”


Julie Hughes
Academy of the Holy Names
English and Language Arts Teacher
Tampa, FL
 Stephanie Killingsworth
Conniston Middle School
Science Teacher
Palm Beach, FL

Intended Audience

Middle School

Time Frame

1 Block Period (90 Minutes)


MS-LS4. Biological evolution: Unity and Diversity

MS-LS4-1. Analyze and interpret data for patterns in fossil record that document the existence, diversity, extinction, and change of life forms throughout the history of life on Earth under the assumption that natural laws operate today as in the past.

MS-ESS2-2. Earth’s Systems

MS-ESS2-2. Construct an explanation based on evidence for how geoscience processes have changed Earth’s surface at varying time and spatial scales.

Constructing explanations and designing solutions in 6-8 builds on K-5 experiences and progresses to include constructing explanations and designing solutions supported by multiple sources of evidence consistent with scientific ideas, principles, and theories.

  • Construct a scientific explanation based on valid and reliable evidence from sources (including the students’ own experiments) and the assumption that theories and laws that describe nature operate today as they did in the past and will continue to do so in the future.
  • The planet’s systems interact over scales that range from microscopic to global in size, and they operate over fractions of a second to billions of years. These interactions have shaped Earth’s history and will determine its future.
  • Water’s movements-both on the land and underground-cause weathering and erosion, which change the land’s surface features and create underground formations.
  • Time, space, and energy phenomena can be observed at various scales using models to study systems that are too large or too small.

Engaging in argument from evidence in 6–8 builds on K–5 experiences and progresses to constructing a convincing argument that supports or refutes claims for either explanations or solutions about the natural and designed world(s).

  • Biodiversity describes the variety of species found in Earth’s terrestrial and oceanic ecosystems. The completeness or integrity of an ecosystem’s biodiversity is often used as a measure of its health.
  • Small changes in one part of a system might cause large changes in another part.
  • Scientific knowledge can describe the consequences of actions but does not necessarily prescribe the decisions that society takes.

CCSS.ELA-LITERACY.RI.6.8: Trace and evaluate the argument and specific claims in a text, distinguishing claims that are supported by reasons and evidence from claims that are not.

CCSS.ELA-LITERACY.RST.6-8.1: Cite specific textual evidence to support analysis of science and technical texts.

CCSS.ELA-LITERACY.RST.6-8.2: Determine the central ideas or conclusions of a text; provide an accurate summary of the text distinct from prior knowledge or opinions.

CCSS.ELA-LITERACY.RST.6-8.9: Compare and contrast the information gained from experiments, simulations, video, or multimedia sources with that gained from reading a text on the same topic.

Resources & Materials

  • 2-4 Stuffed Animals (Different Species)
  • Gabi Map
  • Article: “Battle For The Americas
  • Interactive Notebook
  • Graphic Organizer

Main argument:

One sentence to summarize when the isthmus formed a land bridge and why:

Claim 1: (most convincing reason) Claim 2: (another convincing reason)
Evidence from text:
(paraphrased or quoted directly)
Evidence from text:
(paraphrased or quoted directly)
Evidence from text:
(paraphrased or quoted directly)
Evidence from text:
(paraphrased or quoted directly)
Explain the evidence in your own words:

(explain how the text evidence proves the date of the land closure)

Explain the evidence in your own words:

(explain how the text evidence proves the date of the land closure)

Explain the evidence in your own words:

(explain how the text evidence proves the date of the land closure)

Explain the evidence in your own words:

(explain how the text evidence proves the date of the land closure)

Download Main Argument Work Sheet

Key Academic and/or Scientific Language



Climate change

Continental collision

Deep water connections


Elegant analog






Herald species




IsthmusLand bridge








Salvage paleontology





Volcanic arc

Guiding questions

  • Why is the closing of the isthmus at Panama considered one of the most important geological events over the last 60 million years?
  • What would be different today if the isthmus had not formed?
  • What are some of the results of the isthmus closure (terrestrial, marine, climate)?
  • What are some of the implications with the time differences in the full closure of the isthmus?
  • How do fossils provide evidence of one side of the debate or the other?
  • How were the various species affected who migrated northwards versus those who migrated southwards?
  • Who is Alfred Russel Wallace, and what is he recognized for?
  • What does Coates predict will happen between Indonesia and Australia?


Analyze and evaluate two competing theories about the rise of the isthmus of Panama, and defend one theory using evidence from the text documents.


Formative: Teacher monitoring for understanding through group text marking and reading. Checking for understanding through graphic organizer.

Summative: Group oral defense/argument and peer questioning and interactive notebook reflection.

Teaching Phase

ENGAGE: 10 mins

Divide your class into two groups, each group on either end of the classroom. Label one group “North America” and one group “South America.” Each group will also get a stuffed animal, naming the animal as fauna and reminding students that each animal represents a species. Explain that right now the land and animals are isolated, meaning they are separate and not connected, because of deep water connections. Explain that deep water connections are more than 1,000m with strong underwater currents (not from the wind). Slowly have each group demonstrate uplift by getting bigger and the land masses growing closer to each other until there is continental collision. Finally, the kids will form a true land bridge, connecting the two continents, and forming an isthmus. Then, have the students pass the animals between the continents, demonstrating migration of animals from North America to South America and South America to North America. Explain that when the different species started to travel between the two continents started the Great American Biotic Interchange (GABI).

EXPLORE: 30 mins

Explain that there is currently a big debate within the scientific community about when this event happened. Everyone agrees that the continents were separated and then collided to form the isthmus of Panama, but when it happened is debatable. The “traditional argument” is that the land bridge formed 3.5 million years ago. This is an earlier argument because it is more recent than the “new argument” which says the land bridge formed 10-15 million years ago, much later than the first argument.

Read “The Battle for the Americas” one time through. Depending on the group, consider reading the article aloud so students hear the academic vocabulary before reading it independently. If students are able, consider having them read the article in groups. A detailed “How to read this article” teacher guide is attached at the bottom of this lesson plan.

While reading, all students should stop and write the “gist” at key points throughout the article. This will help students understand, at a cursory level, the claims behind each hypothesis.

EXPLAIN- 15 mins

Students work in small groups to select a side of the debate to defend, by filling in a graphic organizer to sort through the evidence of the text and make discussion smoother.

ELABORATE- 30 mins

Students defend their theory to the class and demonstrate understanding of the concepts within the article and the debate by enduring peer questioning and discourse.

EVALUATE- Homework

Students will write a reflection on the article, its evidence for both arguments, the class discourse, and additional thoughts from the experience of peer review/debate and scientific discourse. The reflection will be completed in student interactive science notebooks, and be evaluated by the teacher for a cohesive understanding of achieving the lesson objective.

Reading | Writing | Speaking | Listening Strategies

Teacher Guide: “How to read this article”

First page (pg. 230)

  • Provide students with the overview that there is currently a heated scientific debate between different groups of scientists who believe the isthmus formed at two different geological time periods.
  • Read the first two columns, and then stop after the second column of text and ask students to write a gist. The basic idea is that fossil records show that the land bridge fully formed 3-4 mya, but that some “herald” species may have come across the continents sooner.
  • Finish reading the last column on the first page and write a gist. The basic idea is that a group of scientists actually dated the rocks in Panama and show that they are much older, and that the land bridge started forming 15 mya and fully formed by 5 mya.

Second page into third (pg. 231-232)

  • Read the first three paragraph in the first column. Box in the second paragraph, and explain that this is the reason why the debate matters. The forming of the isthmus is one of the most important recorded geologic events in Earth’s history, and that many models have been built around the 3.5 mya hypothesis. If wrong, scientists would have to change a lot of the current models (ocean currents, climate, biodiversity) that have been created. Talk about this idea and have students write the gist next to the paragraph.
  • “Oceans of Evidence” – this subheading explains the main claims of the 3.5 mya hypothesis, or a later closure. There is evidence from the oceans (from oxygen isotopes in fossil shells) that shows the salinity started to change between oceans around 4 mya, that ocean currents started to change around 3 mya, and that sea life diversity exploded around 3.5 mya. Point out that the last paragraph in this subheading summarizes the whole argument. The author purposely laid out all of the evidence and then summarized it for the reader before moving on to the second hypothesis.
  • “Putting the s in isthmus – this subheading explains the main claims of the 10-12 mya hypothesis, or earlier closure. Scientists used chemistry to date rock formations and found that the volcanic arc in between the two continents started forming around 70 mya, and that around 25 mya the volcanic arc “melded with the rest of Central America to form a peninsula” (p.232). Point out that again, the author uses the last paragraph in this subheading to summarize the argument.

Third page (p. 232) and Fourth page (p. 233)

  • “Wallace would be proud” – This section explains how Coates (later isthmus closure-traditional theory proponent) doesn’t deny the early phases of Jaramillo’s new theory. Rather he states the fundamental problem is their data can’t confirm whether parts of the arc were still submerged or not.       He states you can’t rule out a deep-water gap in the arc to explain late biotic interchange. He uses the example of Indonesia’s many islands and the migration of species in this modern analog. Specifically, that something similar to a “Wallace Line” existed preventing fauna from moving across.
  • Text box – “Salvage paleontology on the seaway”- The very GABI-RET and PCP-PIRE project and the salvage paleontology happening during the brief excavation window for the Panama Canal expansion is discussed in this text box.

Graphic organizer

To complete this graphic organizer, students must sum up the claims of each hypothesis into one cohesive argument for the top box. They will then select the two best claims, or reasons, why scientists believe the land bridge closed at that time. Students will then pick 1-2 pieces of text evidence to support each claim and explain how the text evidence supports the main argument.

* It may be easier to start by labeling the graphic organizer with the date of the isthmus closing on top, then think about the reasons (claims), and then use the two claims to sum up the main argument.

  1. Sample completed graphic organizer to support 10-12 mya isthmus closing
    sample01: older closing.
  2. Sample completed graphic organizer to support 3.5 mya isthmus closing
    sample02: younger closing.

Learning Progression

Prior Knowledge needed for this lesson:

Nature of science skills, specifically that new evidence can change accepted theories.

Current Knowledge/Skills:

For language arts standards, the ability to trace and evaluate arguments and cite specific evidence to support is strongly practiced with this lesson.

Future Skills Connections:

This lesson has several places during the school year that it could fit well with science curriculum (Nature of Science, Earth’s History, Structure, and Materials, and Evolution). Teachers could use their discretion on when to incorporate, or even whether to circle back on the content on the activity when necessary.

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