Week 10

Describe how Earth formed, its age, and its layers.

Earth formed from dust and gas about 4.6 billion years ago. Layers are crust (outer), mantle (middle), core (inner).

Describe plate tectonics and plate boundaries

Earth’s plates move slowly on the mantle.

• Divergent: plates move apart → new crust forms

• Convergent: plates collide → mountains or subduction

• Transform: plates slide past → earthquakes

Describe the rock cycle and rock types.

Rocks change over time:

• Igneous: from cooled magma/lava

• Sedimentary: from compressed sediments

• Metamorphic: changed by heat/pressure

Weathering breaks rocks down. Rocks are made of minerals.

Describe minerals and how hardness is measured.

Minerals are natural, solid, inorganic substances with a set structure. Hardness is measured by the Mohs scale (1–10).

Describe soil, how it forms, and its importance.

Soil forms from weathered rock and organic matter. It contains minerals, water, air, and organic material.

What are soil horizons?

• O: organic material

• A: topsoil (most nutrients)

• B: subsoil

• C: parent material

Why is soil important to plants?

Provides nutrients, water, and support for plant growth.