Complexity of Life on Earth
Driving Question: How did complexity increase as life on Earth emerged?
For about the first billion years, Earth was a fiery ball of lava—much too hot for anything to live. But about 3.8 billion years ago, things changed. The Earth cooled and life emerged and evolved.
Learning Objectives:
- Describe how life on Earth changed over time.
- Explain the differences between life and nonlife.
- Investigate how complexity increased as life evolved on Earth.
Vocab Terms:
- DNA
- energy
- life
- metabolism
- reproduction
- RNA
- self-maintenance
The Unit Notebook appears in the first lesson of every unit. Not only is it a way for students to preview the unit’s content, it’s also a chance for informal writing. For more support on informal writing, including its benefits, check out the first two pages of the Writing Guide.
You’re alive and you’re here on Earth, which makes you part of a proud 3.5-billion-year tradition. It’s time to learn about your very distant relatives.
Fish didn’t become fish overnight! This next comic and activity show you how Earth’s earliest inhabitants began to evolve.
Before introducing students to Threshold 5: Life, have them review Thresholds 1–4 to see how complexity increases as they learn about the ingredients and Goldilocks Conditions for life on Earth.
There are still some mysteries surrounding how life first appeared—watch this video and fill out the Threshold 5 card to do some investigating!
Want to give your students options for how they read this article? Choose different Lexile levels using the “Version” drop-down menu in the upper-left corner of the article and access the audio by clicking on the speaker icon in the upper-right corner. Find more reading supports on pages 3–5 of our Reading Guide.
What does it mean to be alive? What’s the difference between something that’s alive and something that isn’t? You’re about to get some useful answers to questions you may have never thought of asking.
-
Guiding Questions
-
Before you read
Preview the questions below, and then skim the article. Be sure to look at the section headings and any images.
While you read
Look for answers to these questions:
- Why is self-generation an important characteristic of living organisms?
- How is self-maintenance different for plants and animals?
- What is a genome?
- What are the pros and cons of genetic mutations?
- How does purpose (having goals) distinguish life from nonlife?
After you read
Respond to this question: What are two similarities and two differences between life and nonlife?
For a fun variation that gets kids up out of their seats, set up stations around the room for each DNA percentage. As you call out each organism, have students move to the percentage they think matches with that organism. You could also do a riff on “Pin the Tail on the Donkey” by using Post-it notes to pin the DNA percentage on the organism.
Your DNA is an index of all the unique things that make you...well, you. But did you know you share a lot of your DNA with many different organisms on Earth? Get ready to discover some surprising connections!
