Year 8 Science — Earth & Space (Term 1, Weeks 1-6) Summary & Study Notes

🌍 Unit Overview

This unit explores the structure of the Earth, the three major rock types, how rocks and fossils form, and the processes that shape Earth’s surface. Focus is on observation, classification, and evidence-based explanations for geological events.

🪨 Rocks & Minerals — Key Concepts

Rocks are made of one or more minerals. Minerals are naturally occurring, inorganic solids with a specific chemical composition and crystal structure. Common physical properties used to identify minerals include colour, streak, lustre, density, and hardness.

🔎 Identifying Minerals

Use a key or dichotomous table to identify minerals based on observable properties. Tests include:

• Colour: visible hue, but can be misleading.
• Streak: colour of the powdered mineral (use a streak plate).
• Lustre: how light reflects (metallic, glassy, dull).
• Density: mass per unit volume; heavier minerals feel dense for their size.
• Hardness: resistance to scratching. Use the Mohs scale to compare common minerals.

🪨 The Mohs Scale

The Mohs scale ranks minerals from 1 (softest, e.g. talc) to 10 (hardest, diamond). Compare an unknown by seeing which reference minerals it can scratch and which scratch it. This gives a relative hardness value.

🔥 Igneous Rocks

Formed from cooling and solidification of molten rock (magma or lava). Key features:

• Crystals: size depends on cooling rate—slow cooling (intrusive) produces large crystals; rapid cooling (extrusive) produces small or no crystals.
• Intrusive (plutonic) rocks: form beneath the surface (e.g. granite), coarse-grained.
• Extrusive (volcanic) rocks: form at the surface (e.g. basalt), fine-grained or glassy.

🪨 Sedimentary Rocks

Formed from compaction and cementation of sediments. Characteristics:

• Often layered (stratification).
• May contain fossils or fragments of other rocks.
• Examples include sandstone, limestone, and shale.
• Form through weathering, erosion, deposition, compaction and cementation.

🔧 Metamorphic Rocks

Formed when existing rocks are subjected to heat and pressure, causing recrystallisation and sometimes foliation (banding). Examples:

• Slate (from shale) — fine foliation.
• Schist — visible mineral alignment.
• Marble (from limestone) — recrystallised calcite, non-foliated.

🦴 Fossils & Geological Time

Fossils are remains or traces of past life preserved in sedimentary rocks. Fossil evidence helps predict the age and environment of rock formation and can show how life and continents have changed over time.

♻️ The Rock Cycle (Model)

The rock cycle links all rock types through processes: weathering, erosion, deposition, compaction and cementation, melting, cooling, and heat & pressure. Rocks can move between types depending on conditions.

🌱 Weathering Processes

• Biological weathering: caused by organisms (plant roots, burrowing animals).
• Chemical weathering: breakdown due to chemical reactions (e.g. acid rain dissolving limestone). Both weaken rocks and produce sediments.

🌋 Plate Tectonics & Earth's Structure

Basic Earth layers: crust, mantle, core. The crust is broken into moving plates. The plate tectonics theory explains continental drift and many geological features.

🔄 Evidence for Plate Tectonics

Key evidence: fossil distribution across continents, sea-floor spreading, and mantle processes like convection currents. Forces such as ridge pull and slab pull help move plates.

⚖️ Plate Boundaries & Landforms

Three main boundary types:

• Divergent: plates move apart — mid-ocean ridges and new crust form.
• Convergent: plates collide — mountains, volcanic arcs, and subduction zones form.
• Transform: plates slide past each other — earthquakes are common. Each boundary produces characteristic features (volcanoes, earthquakes, trenches, ridges).

🗺️ Maps, Graphs & Keys

Use maps to identify tectonic activity patterns (earthquakes, volcanoes). Skills to practise:

• Drawing and interpreting classification keys (tables and branching dichotomous keys).
• Drawing graphs, labelling axes, and identifying trends or patterns.

⛏️ Mining in Western Australia & Indigenous Knowledge

Understand methods used to locate and extract minerals (exploration, drilling, open-cut and underground mining) and evaluate benefits (jobs, resources) and costs (environmental impact, social effects). Recognise traditional uses of rocks by Indigenous and Torres Strait Islander peoples (tools, grinding stones, ochres) and how rock properties suit these uses.

✅ Assessment & Skills Focus

Assessments: mid-topic test (Tuesday 17th February, 10%) and end-of-topic test (Thursday 5th March, 12%). Focus on accurate observation, clear diagrams, correct use of keys, and evidence-based explanations.