4.1 - What was young Earth like? - islandschoolhistory

Lesson Purpose

Scientists estimate that the Earth formed about 4.56 billion years ago. The Earth that we know today, the relatively peaceful home of myriad forms of life, didn't appear overnight. Rather, it took billions of years to slowly evolve into its current form. The process of accretion that led to the formation of the Earth was a violent one, and it produced an Earth that was only a little less violent and hostile. For a few hundred million years, the early Earth was characterised by high temperatures, toxic gases, high levels of radiation, and ongoing high-impact collisions. Over time, these conditions improved and the Earth took on its distinctive structure with differentiated layers of core, mantle, crust, and atmosphere. This distinctive structure has important consequences: First, it helps explain why the surface of the Earth changes over time; and second, it helps explain why the Earth evolved into a suitable setting for living things.

The outcomes of this lesson are: 1.) To explain how the Earth formed and the environment changed over time; 2.) To explain how the Earth's atmosphere formed.

Activity 1 - It's Alive! The Universe Verse Book 2

Activity Purpose
In Lesson 1.2, you read part of The Universe Verse, a comic book that illustrates many of the key elements of the Big History story. This second book tells the story of the formation of planet Earth and the emergence of life. This activity invites you to review the comic to get a very quick understanding of how the Earth was formed before moving on to the rest of the lesson.

Activity Tasks

Download and read: It's Alive! The Universe Verse Book 2. When finished, try to answer the following questions:
1. What stands out from the first few pages covering the earlier thresholds?
2. What do we learn about the early Earth?
3. What do we think we’ll learn in this lesson that explains the early Earth in more detail?

Activity 2 - What was young Earth like?

Activity Purpose
This video explains what life was like on the early Earth and asks us to think about what it would have been like to live on the Earth back then. It wasn’t pleasant, and it highlights the challenges emerging life forms had to overcome to survive. This video also previews the idea of plate tectonics, which will be the focus of the next two lessons in this unit. Understanding both the history of the Earth and plate tectonics are critical to understanding how the Earth became a place that could support life.

Activity Tasks

Watch the video and try to answer the following questions:

1:08 What challenges would humans have faced if they lived on the early Earth?
2:23 Why was the early Earth so hot?
3:57 Why is it important that the inner core of the Earth is metal?
4:18 How is the mantle different from the core of the Earth?
4:40 How is the crust different from the mantle?
4:47 How did the Earth’s atmosphere form?
6:18 What important hypothesis did Alfred Wegener make about the Earth, and what was his evidence?
6:33 What was this supercontinent called?
7:04 Why were many scientists unwilling to accept Wegener’s hypothesis?
7:59 When and how did an explanation for the movement of the Earth’s plates come together?
8:57 How does continental crust differ from oceanic crust?
9:37 How were the Andes and Himalayas formed?
10:59 What is plate tectonics?
Discuss - Is the Earth is still forming today?
Discuss - Can you think of other examples of accretion elsewhere in the Solar System?

The layers of the Earth were – and still are – constantly moving, and it was this movement that resulted in the creation of separate continents. Life on each of the continents evolved independently until the continents were reunited much, much later in our story.

Activity 3 - The Early Atmosphere

The atmosphere of the Earth keeps changing and adapting to the conditions around it. There is a never-ending cycle of warming, cooling, and recovery from traumatic events.

Activity Objectives
The atmosphere, like the Earth, has evolved over time. These changes in the atmosphere can be traced to changes on Earth. Many factors can influence the climate, but geological forces such as increased volcanic activity, and biological changes such as the development of photosynthesis, are two examples. It’s important to understand that the atmosphere is part of a larger system, and changes in that system can bring about changes in the atmosphere.

Activity Tasks

Watch the video and try to answer the following questions:
1. 0:37 How did the first atmosphere of the Earth form?
2. 0:48 What is the “greenhouse effect,” and how did the conditions on the early Earth allow for its development?
3. 1:41 How did the formation of the Moon impact the Earth?
4. 2:11 How did the Earth’s atmosphere change during the Hadean eon?
5. 3:07 How did the Earth’s atmosphere change during the Archaean eon?
6. 3:55 What was the Great Oxidation Event and why did it happen?
7. 4:50 How did the buildup of oxygen in the atmosphere impact that Earth’s climate?
8. Discuss - Apart from Oxygen, can you think of other examples of elements or substances that are deadly to some species and not others?

Activity 4 - Evaluating Writing

Activity Objectives
You will be evaluating “Early Earth,” a sample Big History essay, using the rubric that will be used to grade your own writing in the course. The goal of this activity is to familiarize you with the rubric by asking you to review the rubric’s categories and the descriptions of the standards by applying them to a sample paper.

Activity Tasks

Read and discuss the Big History writing rubric on this page, looking at the five categories used to evaluate written work.
When you have finished, read this essay and mark it using the writing rubric.
Now share your grade choices with the class, explaining the reasons for your choices.

Activity 5 - The Driving Question Notebook

Activity Objectives
By now, you should be familiar with the DQ Notebook activity. Although you won’t have much background to inform your work yet, it’s important that you begin to think about what you already know about this unit’s driving question.

Activity Tasks

Download the DQ notebook for our driving question of this unit: 'How and why do theories become generally accepted?'
Think about this question and respond to it by noting down your initial ideas in the first column - we will revisit it in later lessons.

Challenge Yourself! - Optional Activities

1. The Hadean was Earth's first geologic eon and lasted from 4.5 to 4 billion years ago. Named for the Greek god Hades, ruler of the underworld, it was a hellish and extremely violent time in our planet's early history.
2. Panthalassa is the name for the vast global ocean that surrounded the supercontinent Pangaea. It means "all" and "ocean" in a Greek.
3. Earth's early atmosphere was a noxious mix of hydrogen and helium, methane and ammonia. Today's atmosphere is a friendly-to-us mix of nitrogen, oxygen, and argon with traces of carbon dioxide, neon, and helium.
4. Ever noticed rocks with thin layers of red running through? It's probably a banded iron formation, a result of the Great Oxygenation Event that occurred 2.4 billion years ago.

TAKE THE QUIZ!