This activity presents the driving question for Unit 5. It’s meant to help you stay focused on this question as you learn new material.

Driving question: How and why do theories evolve?

Use the DQ Notebook Worksheet – Unit 5 to write about how you think we’re still evolving. You might feel a little lost given that there hasn’t been any content related to this topic yet; however, just use what you know and what you think, and answer to the best of your ability.

Did you know that all living things on Earth share a common ancestor? That’s pretty amazing, but what’s even more exciting is how we discovered these connections. From the birth of life in deep ocean vents to the variety of life on Earth today, our understanding of how life evolved has changed, or evolved, over time. In this overview video, Rachel Hansen explores the origins of life and how it evolved over 4 billion years of history.

This unit is all about life—how it originated and evolved and how all living things are connected. You’ll learn about how we define life and the common characteristics shared by all lifeforms on this planet. You’ll also learn how our understanding of life has changed over time thanks to collective learning.

Preview

As a reminder, open and skim the transcript, and read the questions before you watch the video.

Key Ideas – Factual

Think about the following questions as you watch this video:

1. Why do we share DNA with all other forms of life on Earth?
2. How has our understanding of DNA impacted history and human communities?
3. What is the Human Genome Project and why is it important?
4. How does Big History define life?
5. What is the most accepted theory for how life on Earth first began?
6. How do life and the Earth impact each other?
7. How do we know about the origins and evolution of life?

Thinking Conceptually

1. Rachel gives a few examples of how life and Earth interact. Can you think of other examples of how life impacts Earth or how Earth and our Solar System impact life?
2. While the most accepted theory for how life began on Earth is around deep oceanic vents, there are other theories. Choose one other theory to investigate and use your claim testing skills to assess its probability.

Understanding vocabulary helps you access course content and become a better reader, a better writer, and a better communicator. This word wall activity will help you begin to learn some of the key vocabulary from the unit.

In this activity, you’ll work with your class to create a word wall using the Unit 5 vocabulary.

Your teacher will assign a vocab card to each of you. Once you get yours, take a few minutes to look it up in the Vocab Guide and then examine the unit itself (click around and quickly skim the content) to see where in the unit your word might be most applicable. Then, add as many antonyms to your card for your word as possible. Be careful if you decide to use the “related words” section from the vocab guide—it doesn’t distinguish between synonyms and antonyms. Your teacher will give you a limited amount of time to write antonyms. Then, the people with the most correct antonyms at the end of the time will put their words on the word wall first.

Your teacher may add some fun twists to this assignment, so be sure to listen closely for directions!

The emergence of life on Earth is a truly amazing development in the history of the Universe. And the fact that a chemical reaction in the oceans eventually resulted in something as complex as ourselves is nearly mind-boggling. It’s no wonder that life is one of Big History’s thresholds of increasing complexity!

Clip 27:08-41:14. This video introduces you to the emergence of life on Earth. Understanding how life emerged from nonlife can be confusing, and this video gives one explanation of how this process occurred, and what happened as life evolved.

Preview

Life on Earth started as a chemical reaction in the deepest depths of the oceans billions of years ago. About 500 million years ago, development of plant and animal life in the oceans took off. Over time, life moved from the oceans onto the land and evolved into many different forms.

Key Ideas – Factual

Think about the following questions as you watch the video:

1. What do most people believe is the reason for the emergence of life on Earth?
2. What is the biological blueprint for everything that exists?
3. What is the earliest form of life?
4. Why is the egg a critical development?
5. What did the extinction of the dinosaurs clear the way for?
6. What did humans ultimately evolve from?
7. How did primates take the first step toward being human?

Thinking Conceptually

Consider the possibility of a new species emerging on Earth. Based on what you learned from the video, do certain things need to happen for new species to evolve? If so, what are those things?

This activity will help you understand the relationship between different species, and show you how we (humans) are related to other species. The evolution of life from bacteria to humans is pretty hard to wrap your mind around, and showing connections among different species will increase your understanding.

Look at the How Closely Related Are We? Worksheet and try to match the list of organisms with the percentage of DNA shared with humans.

Do the numbers make sense to you? Why, for example, do they think we are more closely related to a plant than bacteria? Are you surprised at how much DNA we have in common with chimps and zebrafish?

DNA is the most important characteristic of all living things. It is essential to the story of life. Understanding the complexities of it are not essential to the Big History story; however, understanding its importance to life is. Try not to get too bogged down in the details, especially since scientists are still trying to work out how this molecule became the master blueprint of all life on Earth.

Crash Course Big History Episode #4. This Crash Course video explains key information for Threshold 5: Life, such as the characteristics of living things, how life emerged on Earth, and the importance of DNA.

Preview

It’s not always easy to see the close connections humans share with other species. Sometimes, the connections are detectable only at the genetic level; but the connections are there, nonetheless. What is it that connects humans with other species? DNA is one important ingredient—after all, DNA is something that all living things share. There are other key characteristics that most living things share with each other, and these are what make living organisms different from nonliving.

Key Ideas – Factual

Think about the following questions as you watch the video:

1. What is one of the biggest puzzles about life that we have yet to figure out?
2. Hank talks about the definition of life at least three times. So, what is life?
3. How was Friedrich Wohler’s chemistry experiment important in the discovery of where life originated?
4. What forms of life dominated Earth for the vast majority of its existence?
5. How can oxygen be harmful and how did it change life?
6. What makes eukaryotes more complex?
7. What makes DNA such an important molecule, and where did it originate?

Thinking Conceptually

In the video, John talks about some of the theories about how life on Earth began. Which of these do you think is the most plausible, and why? Can you think of another explanation?

In this article, Goodenough presents the four characteristics that she believes define living things. Scholars don’t always choose the same words to talk about a subject, so we are able to gain a different perspective from that of the Crash Course video. In addition, Goodenough asks philosophical questions about what it means to be alive.

You’re about to be introduced to another way of defining what it means to be living. As you have already learned in the course, different scholars, especially those from different disciplines, may approach the same subject from a different angle, or use different words to describe the same thing. This is a great example of that process.

Skimming for Gist

Fill out the Skimming for Gist section of the Three Close Reads Worksheet as you do your first close read.

Understanding Content

You should be able to answer these questions by the end of your second close read:

1. What does Goodenough mean by self-generation?
2. What does Goodenough mean by self-maintenance? Is this the same as the process Hank calls metabolism?
3. What does Goodenough mean when she says “Every organism is instructed”? Is this the same as the process Hank calls reproduction?
4. What does Goodenough mean when she says “Every organism evolves”? Is this the same as the process Hank calls adaptation?

Thinking Conceptually

In the article, Goodenough writes about how “the most interesting single generalization is that organisms are purposive whereas nonlife is not.” What do you think she means by this? This is a hard question and good for a whole class discussion using the Discussion Quick Guide. Practice pressing your fellow classmates for justification during this discussion!