7  Unit 2: Opening — Are We Alone?

Does life exist somewhere outside Earth? What about intelligent life?

Unit 2 Time: 2 Days

👽 Are We Alone in the Universe? 👽

8 The Anchor Phenomenon

8.1 🌌 4.5 Billion Years of Cosmic Patience

4.5 billion years passed and 5 mass extinctions occurred before intelligent life evolved on Earth. So far, we’ve found zero evidence of life anywhere else. Are we alone?

The Numbers:

• 🌟 There are roughly 200 billion trillion (\(2 \times 10^{23}\)) stars in the observable universe
• 🪐 Most stars have planets — that’s potentially trillions of planets
• 🦠 Life appeared on Earth relatively quickly (~500 million years after formation)
• 🧠 But intelligent life took 4.5 billion years — and required 5 mass extinctions
• 📡 Despite decades of searching (SETI), we’ve detected zero signals from other civilizations

8.1.1 The Fermi Paradox

If the universe is so vast and old, and life appeared relatively quickly on Earth… where is everybody?

Plot = require("@observablehq/plot")
d3 = require("d3@7")

timeline = [
  {event: "Earth forms", time: -4500, duration: 0, color: "#e74c3c", y: 0},
  {event: "First life (bacteria)", time: -3800, duration: 0, color: "#2ecc71", y: 1},
  {event: "Oxygen rises", time: -2400, duration: 0, color: "#3498db", y: 2},
  {event: "First complex cells", time: -2000, duration: 0, color: "#9b59b6", y: 3},
  {event: "Cambrian Explosion", time: -540, duration: 0, color: "#f39c12", y: 4},
  {event: "First land animals", time: -430, duration: 0, color: "#e67e22", y: 5},
  {event: "Dinosaur extinction", time: -66, duration: 0, color: "#e74c3c", y: 6},
  {event: "Modern humans", time: -0.3, duration: 0, color: "#00cec9", y: 7}
]

Plot.plot({
  title: "Timeline of Life on Earth (millions of years ago)",
  subtitle: "Intelligent life is the product of 4.5 billion years of evolution",
  width: 700,
  height: 350,
  marginLeft: 160,
  x: {label: "Millions of years ago", reverse: true, grid: true},
  y: {label: null},
  marks: [
    Plot.dot(timeline, {
      x: d => -d.time,
      y: "event",
      fill: "color",
      r: 8
    ,
        tip: true}),
    Plot.text(timeline, {
      x: d => -d.time,
      y: "event",
      text: d => `${Math.abs(d.time)} Mya`,
      dx: 15,
      fontSize: 10,
      fontWeight: "bold"
    }),
    Plot.ruleX([0], {stroke: "#00cec9", strokeWidth: 2, strokeDasharray: "5,5"})
  ]
})

🧠 If Earth’s 4.5-billion-year history were compressed into a single 24-hour day, modern humans wouldn’t appear until the last 0.2 seconds before midnight. Life is ancient. Intelligence is brand new.

8.1.2 📝 Your Initial Ideas

1. Do you think life exists somewhere outside Earth? What about intelligent life? Why or why not?
2. If life does exist elsewhere, why haven’t we detected it yet? List at least 3 possible explanations.
3. What conditions on Earth do you think were necessary for life to evolve? Make a list.
4. Write at least 3 questions for the Driving Question Board.

8.1.3 🎯 Performance Task Preview

By the end of this unit, you’ll use your findings to develop an explanation for why it took 4.5 billion years for modern humans to emerge, then argue whether life or intelligent life exists somewhere outside Earth — and why we haven’t made contact.

8.1.4 📋 Driving Question Board Starters

• Why are there so many craters on the Moon but not on Earth?
• How did asteroid impacts affect the evolution of life?
• How did Earth’s atmosphere change over time, and how did life cause those changes?
• Where did all the matter in the universe come from?
• Will a major asteroid ever hit Earth again?