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The Formation of Earth
How did a swirling cloud of rock and dust become the world we live on?

Four and a half billion years ago, Earth was a swirling cloud of hot dust and gas. Over time, gravity pulled everything together, the planet heated up, and eventually (amazingly) it cooled enough to form a solid crust. In this lesson, your learner will explore how Earth formed and what its interior looks like, discovering that the ground beneath their feet is just a thin shell around a planet still alive with heat and movement.

S2S_Lesson05_FORMATION_OF_EARTH.pptx by Selene

Key Ideas

  • Earth formed from a cloud of gas and dust that came together billions of years ago.
  • Early Earth was very hot (almost completely melted) and has slowly cooled over time.
  • When Earth was young and melted, heavier materials sank to the center and lighter materials floated to the top.
  • The core is the hottest and densest part; the mantle is still very hot but not fully liquid; the crust is where we live.
  • Understanding Earth's layers helps us understand volcanoes, earthquakes, and how our planet is always changing.

Spine Reading
✏️  Notebooking Activity
Label the diagram of Earth’s layers (core, mantle, crust) and write the general thickness of each layer.

Cosmic Calendar Where we are: September 14
We are still in September, just five days after the solar system formed. Read the script below before the lesson.

Read aloud: We’re still in September on our Cosmic Calendar, but we’ve moved forward a few days. Last lesson we talked about gravity as a concept that has no single date. Today we’re back on the timeline, and we’ve landed on September 14th. That’s when Earth formed, about 4.5 billion years ago in real time. Our solar system came together on September 9th, and just five days later on the calendar, Earth had taken shape. Five cosmic days. In real time that’s about 70 million years between the formation of the solar system and the formation of Earth itself. Fast in cosmic terms, but still longer than the time since the dinosaurs went extinct. We have a planet now. Everything that comes next happens right here.

Timeline PageLabel the next page in your timeline “Formation of Earth: 4.5 Billion Years Ago”. The workbook prompt asks learners to draw a young, molten Earth being pelted by asteroids from the surrounding cloud of space debris.

SCIENTIST SPOTLIGHT: Inge Lehmann
Inge Lehmann was a Danish seismologist who, in 1936, discovered that the Earth has a solid inner core. Before her work, scientists believed the entire core was liquid. Lehmann analyzed earthquake wave data and noticed that the waves were behaving in a way that only made sense if there was a solid sphere at the very center of the Earth. She did this work largely by hand, sorting paper cards on her kitchen floor. She worked in a field dominated by men, was denied access to many professional organizations for much of her career, and continued publishing research until she was well into her nineties. She died in 1993 at the age of 104.

Videos:
Icons In Discovery: Inge Lehmann
A Seismic Discovery: How Inge Lehmann Cracked Earth's Heart!

Digging Deeper Activity:
How do seismologists use earthquake waves to learn about the inside of the Earth? Draw a diagram of the Earth’s layers and label what Lehmann discovered. Why is it so hard to study the interior of the Earth directly?

VocabularyAccretion — The gradual build-up of a planet through repeated collisions of smaller rocks and dust, pulled together by gravity.
Molten — Melted into liquid form by extreme heat; early Earth was entirely molten due to constant collisions and radioactive heating.
Core — The innermost layer of Earth, made mostly of iron and nickel; the inner core is solid and the outer core is liquid.
Mantle — The thick layer of rock between Earth's core and crust; solid but flows very slowly over millions of years.
Crust — The thin, outermost layer of Earth where we live; made of cooled rock and broken into tectonic plates.
Differentiation — The process by which heavier materials sank to Earth's center and lighter materials floated to the surface as Earth cooled.
Volcanic Outgassing — The release of gases like water vapor and CO2 from volcanoes, which helped form Earth's early atmosphere and oceans.

Sources

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