Earth's Systems and Matter

You've got your brain switched on and a map in hand. Now it's time to check your inventory. What's this planet actually made of, and how do all the parts work together?

Matter is anything that has mass and takes up space. Rocks, water, air, you. All matter.

Mass is how much matter something has. A bowling ball has more mass than a beach ball, even though they're about the same size.

Matter is built from tiny pieces called atoms. An atom has three parts:

• Protons: positive charge, in the center (the nucleus).
• Neutrons: no charge, also in the nucleus.
• Electrons: negative charge, zipping around the outside.

An element is a substance made of only one kind of atom, like oxygen, iron or gold. There are 118 known elements, all organized on the periodic table. Think of it as the ultimate crafting chart.

When atoms of different elements bond together, they make a compound. Water (H₂O) is two hydrogen atoms stuck to one oxygen. Table salt is sodium plus chlorine. Fun fact: sodium explodes in water and chlorine is a poison gas. Together they go on your fries.

The force that holds atoms together in a compound is called a chemical bond. Think of it like the glue between blocks. Break the bonds and the compound comes apart into its elements.

Just eight elements make up about 98% of Earth's crust. The top two are a surprise:

1. Oxygen: about 46%. Yes, the crust is mostly oxygen, locked inside rocks.
2. Silicon: about 28%. Oxygen and silicon together form the building blocks of most rocks.
3. Then aluminum, iron, calcium, sodium, potassium and magnesium.

So when you pick up a rock, you're basically holding oxygen in a solid costume.

Matter shows up in different forms, called states:

• Solid: fixed shape. Rocks, ice.
• Liquid: takes the shape of its container. Water, lava.
• Gas: spreads out to fill any space. Air, steam.
• Plasma: super-hot, charged gas. Lightning and the Sun.

Adding or removing energy (usually heat) changes the state. Ice melts into water, water evaporates into vapor. Lava cools into solid rock. Earth does this all day, every day.

Going the other way, when water vapor cools and turns back into liquid droplets, that's condensation. It's why a cold soda can "sweats" on a hot day, and it's how clouds form. Matter and energy keep moving around and around in loops called cycles, like the water cycle and the rock cycle.

Scientists split Earth into four connected systems, called spheres:

• Geosphere: the solid Earth. Rocks, mountains, and everything down to the core.
• Hydrosphere: all the water. Oceans, rivers, lakes, groundwater, ice. About 97% of it is salty ocean water.
• Atmosphere: the blanket of air around Earth. Mostly nitrogen (78%) and oxygen (21%).
• Biosphere: all living things. Plants, animals, bacteria, and you.

The spheres don't work alone. They're constantly trading matter and energy. Here's one example:

A volcano erupts (geosphere). It blasts ash and gas into the sky (atmosphere). Rain washes the ash into rivers (hydrosphere). Years later, that ash turns into rich soil, and plants grow like crazy (biosphere).

One event, all four spheres. That's why Earth scientists call it a system. Change one part, and the rest feel it.

Earth runs on two main power sources:

• The Sun: drives weather, wind, ocean currents, and the water cycle, and feeds almost all life.
• Earth's internal heat: left over from when the planet formed, plus heat from radioactive elements breaking down. It moves plates, builds mountains, and powers volcanoes.

Matter on Earth gets recycled over and over. The water you drink today may have once been dinosaur sweat. Seriously. Same water, new cup.