Field Map · Unit 1

Geology Basics

One page to read the Earth like a book. Its layers tell you what it's made of, its three rock families tell you how each piece formed, its stacked beds tell you how old things are, and its slow movement explains the mountains, faults, and volcanoes. Everything below is a snapshot of the five lessons.

Inside the Earth

Crust 5–70 km thick

The thin, solid rock skin we live on — thinner, next to the whole planet, than an apple's skin. Thick light land, thin dense seafloor.

Mantle ~2,900 km thick

Hot rock that is mostly solid yet flows like stiff putty over millions of years. This slow churning drives most geology.

Outer core liquid metal

Molten iron and nickel. Its swirling motion generates Earth's magnetic field.

Inner core centre ≈ 5,500°C

A ball of solid iron — kept solid not by cold but by the crushing pressure at the planet's heart.

The three rock families & the cycle

Igneous

born from heat

Forms when molten rock cools and hardens. Think "ignite." Granite and basalt.

Sedimentary

built from bits & layers

Bits of older rock settle in layers, get buried, pressed and glued. Sandstone, shale, limestone.

Metamorphic

changed by heat & pressure

An existing rock is cooked and squeezed until it transforms — without melting. Limestone→marble, shale→slate.

Igneous up close: intrusive vs extrusive

Intrusive / plutonic underground

Magma cools slowly, underground, so crystals grow large → coarse, grainy rock like granite. The body of magma itself is an intrusion.

Extrusive / volcanic at the surface

Lava cools fast at the surface, so crystals stay tiny or absent → fine, smooth rock like basalt.

Reading the layers & deep time

How sedimentary rock forms: weathering breaks rock into bits → rivers and wind deposit them in flat layers → burial presses and cements them into strata (beds).

The law of superposition: in undisturbed layers the oldest sits at the bottom, the youngest on top — so a cliff face reads like history, oldest first.

Fossils — traces of ancient life — form almost only in these gentle layers, and help match the ages of far-apart rocks.

4.5 GaEarth forms

66 Madinosaurs out

Nowhumans (very recent)

The restless Earth

Plate tectonics is the big idea that ties it together: Earth's rigid shell is cracked into plates that drift about as fast as your fingernails grow. Where they meet, rock breaks, bends, and melts.

Fault

A crack where two sides have slipped. A sudden slip = an earthquake.

Fold

Layers bent by squeezing instead of breaking. Folds build mountains.

PULLING APART

New crust wells up in the gap — mid-ocean ridges.

PUSHING TOGETHER

Crust crumples into mountains, or dives down to feed volcanoes.

SLIDING PAST

Plates grind sideways — a setting for big earthquakes.

Field glossary

Magma: Molten rock while still underground.
Lava: Molten rock once it reaches the surface.
Lithosphere: The rigid outer shell that forms the plates.
Strata / beds: The layers of sedimentary rock.
Superposition: In undisturbed layers, oldest is at the bottom.
Fault: A crack where rock has slipped; can cause earthquakes.
Fold: Rock layers bent by squeezing, not broken.
Erosion: Wearing away and carrying off rock and soil.
Deposition: Dropping that material in a new place.
Bedrock: The solid rock beneath loose soil.
Outcrop: Where bedrock pokes up to the surface.
Rock cycle: The slow loop between the three rock families.

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