ASVAB General Science Study Guide 1

The ASVAB General Science subtest is designed to test your scientific knowledge. Let's read our lessons and tips for the Science section of the ASVAB to get 100% ready for your coming ASVAB.

The ASVAB General Science subtest is designed to test your scientific knowledge. The subtest is NOT a part of your Armed Forces Qualification Test score. However, if you desire a job field that is related to science, you will need to perform your best on the general science test to qualify for that job.

Because it is a general science test, students must show their general knowledge of a variety of scientific areas, including Earth & Space Science, Life Science, and Physical Science. Each portion of the general test has the same role, make sure you do not focus too heavily on any one area. 

Part 1 of our Free General Science ASVAB Study Guide covers the general information you need to know about Earth & Space Science. This topic will show all the knowledge about the structure of the Earth, Plate tectonics, Types of rocks, Water cycle, Earth’s Atmosphere, Planets, and Comets.

Earth & Space Science

Structure of the Earth

asvab general science

The Earth is consists of three main layers:

The outer silicate solid crust is the rocky outer layer of the Earth. It is very thin (5–70 kilometers in depth) compared to the other two layers.

The Earth’s mantle is the planet’s thickest layer with a depth of 2,890 km. It is a hot, solid rock layer located under the crust.

The core is a large sphere of metal that forms the center of the Earth. It concludes a liquid outer core whose flow produces the Earth’s magnetic field and a solid inner core.

Plates tectonics

Plate tectonics is the theory that Earth’s outermost layer is divided into large slabs of solid rock, called “plates,” that drift slowly. They move at about 1/2 to 4 inches (1.3 to 10 centimeters) per year.

There are two types of plates – oceanic plates and continental plates. As these plates move, the continents glide slowly. Based on the direction of a plate’s movement as well as its relationship to the beside plates, various different boundaries may be formed:

Divergent plate boundaries occur when 2 tectonic plates move away from each other. Here, earthquakes happen commonly and magma (molten rock) from the mantle rises to the surface and creates a new oceanic crust. 

Convergent plate boundaries form when two plates come together and collide. The impact of the colliding plates causes the edges of the plates to buckle up then creating mountain ranges or one of the plates may bend down into a deep seafloor trench.

Transform fault boundaries 

A transform fault or transform boundary occurs when plates move sideways past each other horizontally. It ends suddenly when it connects to another plate boundary, or another transform, a spreading ridge, or a subduction zone.

Types of rocks

In your ASVAB General Science section, you may be asked about the types of rocks as well as their properties. Let’s take a look to obtain this information.

Igneous rock, sedimentary rock, and metamorphic rock are the three main types of rocks.

Igneous rock is formed when magma or lava from inside the earth cools and solidifies. This type of rock majorly makes up the Earth’s crust (ex: basalt, obsidian, and granite).

Sedimentary rock is formed over time when smaller sediments and inorganic material are layered, squeezed, and solidified. (ex: sandstone, limestone, coal, and shale).

Metamorphic rock forms when igneous or sedimentary rock is transformed by heat, pressure, or chemical reactions. (ex: slate, marble, and quartzite).

Water cycle

There is some facts about the water you may need while doing your ASVAB General Science subtest:

Water occupies 71% of Earth’s surface in the oceans, lakes, rivers, and glaciers.

On the Fahrenheit temperature scale, water freezes at 32° and boils at 212°. On the Celsius scale, water freezes at 0°C and boils at 100°C.

Saltwater makes up 97% of the water on Earth. Of 3% of remaining freshwater, and two-thirds of it is ice.

Earth’s liquid freshwater is mainly in the form of groundwater.

asvab general science study guide

The water cycle describes the continuous movement of water to the atmosphere by evaporation and then from the atmosphere to the land by precipitation.

Evaporation: Heats of the sun change water on the Earth’s surface from liquid to gas state. This vapor can then rise up into the atmosphere. Water also evaporates from plants, in a process called transpiration.

Condensation: Water vapor rises into the sky, turning back into a liquid, then forming clouds.

Precipitation is any product of the condensation of water vapor in the atmosphere that falls from clouds. This includes rain, snow, and hail.

Earth’s Atmosphere

This information will help you improve your knowledge about the atmosphere of the Earth and easily solve this kind of question in your ASVAB General Science test.

Earth’s atmosphere is made up of 78% nitrogen, 21% oxygen, 0.9% argon, and 0.1 percent other gases (carbon dioxide, methane, water vapor, and neon).

Layers of the Atmosphere: From lowest to highest, the five main layers are:

Troposphere: This is the lowest layer of the atmosphere where we live in. Weather almost takes place in this layer. In this layer, the higher the distance above the earth is, the colder the temperature gets (by about 6.5°C per kilometer).

Stratosphere: This extends upwards of about 50 km from the troposphere. It contains the Ozone layer. In this zone, due to the absorption of ultraviolet (UV) radiation from the sun by the Ozone layer, temperature increases with height.

The Mesosphere is located above the stratosphere. The temperature here also decreases with height, with the minimum of about -90°C at the “mesopause”.

Thermosphere: The International Space Station orbits lie in this layer. The thermosphere is above the mesopause. In this region, the temperatures again increase with height. This may be caused by the absorption of energetic ultraviolet and X-Ray radiation from the sun.

Exosphere:  The region higher than 500 km is called the exosphere. This region contains mainly oxygen and hydrogen atoms. Most of the satellites orbiting Earth are in here.

The planets

asvab general science study guide

Planet Facts:

The planets can be divided into 2 groups. The first group concluding inner planets that are small, dense, and rocky (Mercury, Venus, Earth, and Mars). Another one consists of 4 planets called the terrestrial planets because of their solid planetary surfaces.

Here are the 8 planets listed in order of nearest distance to the Sun:

Mercury: The smallest of the terrestrial planets in the solar system and the closest to the sun. It is only slightly bigger than the Earth’s Moon. It is also the fastest planet,  taking 88 Earth days to zip one revolution around the sun.

Venus: The brightest object in our night sky following the moon. Venus spins slowly in the opposite direction from most planets. The rate of its rotation is very slow. Venus takes 243 days to rotate around its axis, which is even longer than it takes to complete a revolution around the sun. A very thick atmosphere composed of carbon dioxide and droplets of sulfuric acid traps heat making it the hottest planet.

Earth: Unique from the other planets because it is the only place we know of so far existing living things. Its surface has a suitable condition of atmosphere and temperature for the existence of liquid water to support life.

Mars: A “red planet” with a dusty, cold, desert surface and very thin atmosphere. There is evidence that Mars had a great deal of liquid surface water billions of years ago.

Jupiter: The largest planet in our solar system and more than twice as massive as all other planets in the system combined. It is also the planet with the biggest number of the moon with I79 in total. Jupiter contains major hydrogen and helium. 

Saturn: The second-largest planet in our solar system with a spectacular dazzling, complex system of icy rings. Saturn has 62 moons. 

Uranus: The seventh planet from the Sun – its most unusual characteristic is that the axis is tilted more than 90°. This unique tilt makes Uranus seem to spin on its side.

Neptune: The farthest planet from the Sun – has a bluish color due to the methane in its atmosphere. It is a dark, cold planet and whipped by supersonic winds.


Comets are cosmic snowballs made up of frozen gases, rocks, and dust that orbit the Sun. People are sometimes called Comets “dirty snowballs”. When a comet’s orbit takes it close to the Sun, it begins to heat up and release gases and dust in the outgassing process. This creates a giant glowing head larger than many planets. The dust and gas tail can stretch for millions of miles. 

After reading some knowledge and tips for the ASVAB General Science section, let’s take our practice questions to find out more clearly what you have mastered and what you should improve on! Find our free ASVAB practice test for other sections with us here!

Click here to take our free ASVAB General Science practice tests!