Earth Science — Essential Concepts

Physical Setting/Earth Science Regents quick-reference — the motions of Earth, how we map it, weather, the rock and water cycles, and the forces that shape the surface.

Earth's Motions

• Rotation: spins on its axis once every 24 hours (15°/hour) → day and night.
• Revolution: orbits the Sun once a year in a slightly eccentric ellipse (e ≈ 0.017, nearly circular).
• Seasons: caused by the 23.5° tilt of Earth's axis — NOT by distance from the Sun.
• Polaris's altitude equals your latitude in the Northern Hemisphere.

Mapping Earth

• Latitude = north/south (0°–90°); longitude = east/west (0°–180°).
• Contour lines connect points of equal elevation; closer lines = steeper slope.
• Gradient = change in field value ÷ distance.
• Streams flow downhill; contour lines bend upstream (V points uphill).

Minerals & Rocks

• Mineral: natural, inorganic solid with a definite composition and crystal structure. ID by hardness, cleavage/fracture, luster, streak.
• Igneous: cooled and crystallized from magma/lava.
• Sedimentary: compacted/cemented sediments (often layered, may contain fossils).
• Metamorphic: reshaped by heat and pressure.

Plate Tectonics

• Divergent: plates pull apart (mid-ocean ridges, sea-floor spreading).
• Convergent: plates collide (subduction, trenches, mountains, volcanoes).
• Transform: plates slide past each other (faults, earthquakes).
• Driven by convection currents in the mantle.

Weather & the Atmosphere

• Low pressure (L): rising air → clouds and storms. High pressure (H): sinking air → clear skies.
• Isobars connect equal pressure; closely spaced isobars → strong winds.
• A wind barb points in the direction the wind comes from.
• Air rises, cools to its dew point, water vapor condenses → clouds and precipitation.

Surface Processes

• Weathering breaks rock in place; erosion transports it (water, wind, ice, gravity); deposition drops it.
• Sediments are sorted by size, shape, and density — largest/densest settle first.
• Glaciers carve U-shaped valleys; rivers carve V-shaped valleys.

Common Test Mistakes

• Saying seasons are caused by distance from the Sun (it's the tilt).
• Reading a wind barb as the direction the wind blows toward (it's from).
• Confusing weathering (breakdown) with erosion (transport).
• Forgetting that the epicenter is on the surface, the focus is underground.