Big History Project
- WATCH: How Did Life Begin and Change?
- WATCH: Threshold 5 — Life on Earth Video
- WATCH: Mini Thresholds Of Life
- WATCH: Life In All Its Forms
- READ: The Collector - Ynés Mexía: Graphic Biography
- ACTIVITY: The Tree of Life Infographic
- WATCH: Why the Evolutionary Epic Matters
- READ: Gallery — How Did Life Begin and Change?
- Quiz: How Did Life Begin and Change
WATCH: Threshold 5 — Life on Earth Video
Through a diversity of chemical elements and the perfect conditions on Earth, life mysteriously appeared. Created by Big History Project.
Want to join the conversation?
- Why is the term "Goldilcks Condition" being used?(3 votes)
- The term actually comes from the three bowls of porridge in the Goldilocks and the three bears story. The first was too hot, the second was too cold and the third was just right. So the Goldilocks condition is where a planet is not too hot, or too cold, just perfect.(1 vote)
- How can chemistry turn into life? Does life just, magically appear out of chemistry?(1 vote)
- why almost perfect conditions? what would be more perfect?(1 vote)
- I agree with him we live in awesome conditions winter Christmas then it heats up for us to have fun in summer and play friz bee and sports then gos back so we can snow board and have snow ball fights I think our conditions are perfecto 😜(1 vote)
NARRATOR: Threshold five brings us life. What is life? Though there may be many other life forms in the Universe, we could only study those that emerged on our planet. So, from now on, we focus on our home planet, the Earth. All living things on Earth share important qualities. First, they take in energy from outside to maintain themselves. This is metabolism. Second, they all seem to constantly try to balance the conditions inside and outside themselves in order to survive as long as possible. This is called homeostasis. Third, they can make copies of themselves through reproduction because they all contain huge molecules of DNA or RNA that record how they were made. And fourth, over time, the information in those molecules can change so that later generations may be slightly different. And in this way, living things slowly diversify. Let's consider the ingredients and the Goldilocks conditions needed for life to form. The ingredients are a great variety of complex chemical compounds including DNA and RNA. Two Goldilocks conditions provide ideal environments for these chemical compounds to combine in many different ways. First, you need energy to fuel those chemical reactions but not too much since that would just blast molecules apart. And second, you need a liquid. That's because it's hard for atoms to link up in gases, where they're too far apart, or in solids, where they can't move very much. So where could we find these Goldilocks conditions? Well, liquids can only exist in a narrow range of temperatures. If the temperature is too high, like right next to a star, then liquids turn into gases. If the temperatures are too cold, like in deep space, liquids turn into solids. Some rocky planets or moons are just the right distance from their suns to have lots of liquid water. They also have the right amount of energy to encourage chemical reactions. Here, on our Earth, four billion years ago, you would have found almost perfect conditions for some of the most complex chemistry you can imagine. That chemistry led to life.