What the ASVAB is actually testing
Earth and Space Science questions on GS cover three areas: geology (Earth's structure and rock types), atmospheric science (weather and layers of the atmosphere), and astronomy (solar system, moon phases, eclipses). Questions lean heavily on classification and cause-effect — why do seasons happen, what type of rock is this, what drives weather?
Geology: Earth's layers and the rock cycle
Earth has four main layers. The crust is the thin outer shell we live on. Below it is the mantle, a thick layer of hot, semi-solid rock that moves slowly. The outer core is liquid iron — its convection generates Earth's magnetic field. The inner core is solid iron, despite being hotter, because extreme pressure keeps it solid.
The rock cycle connects three rock families:
- Igneous — magma cools and solidifies (granite, basalt)
- Sedimentary — sediment layers compress over time (sandstone, limestone)
- Metamorphic — existing rock is changed by heat and pressure without melting (marble, slate)
Any rock type can transform into any other given the right conditions.
Atmosphere and weather
The layer you live in is the troposphere — it holds nearly all weather and most of the atmosphere's mass. Above it is the stratosphere, home to the ozone layer. Temperature, pressure, and humidity interact to drive weather: warm air rises (lower pressure), cool air sinks (higher pressure), and wind flows from high pressure to low.
The water cycle is a continuous loop: evaporation → condensation (clouds form) → precipitation → runoff back to water bodies.
Astronomy: what to memorize
For the ASVAB you need to know:
- Planet order and that the first four (terrestrial) are rocky while the outer four are gas giants
- Seasons come from axial tilt, not distance — this is the single most tested astronomy fact
- Solar eclipse: Moon passes between Earth and Sun, blocking sunlight
- Lunar eclipse: Earth passes between Sun and Moon, casting shadow on the Moon
- Moon phases: new moon (dark) → waxing crescent → first quarter → full → waning → new
Study approach
Prioritize cause-effect relationships over lists. If you can explain why seasons happen, why the outer core is liquid, and how sedimentary rock forms, you're covering the reasoning behind most GS earth-space questions.