Ships sailing at the horizon provide evidence that Earth is spherical.

Shadows provide evidence that Earth is spherical.

Gravity is a force directed toward the center of the spherical Earth.

The sun appears larger and brighter than other stars because it is closer.

The Sun's daily motion provides evidence that Earth rotates on an axis.

The daily motion of the stars provides evidence that Earth rotates on an axis.

Some constellations are not visible all year.

Earth's revolution around the Sun causes variation in daylight (Modeling Daylight).

Earth's revolution around the Sun causes variation in daylight (It's Been a Long Day).

Predictable patterns in the night sky can be used to solve a navigational problem.

Solutions to problems are designed to meet criteria and constraints and must be tested to determine which best meets them.

Solutions to problems are designed to meet criteria and constraints but must be implemented correctly to be successful. 

Ancient Polynesians navigated the ocean without instruments.

Observations of the sky can be used to navigate a boat.

Scientific arguments are based on evidence.

Properties can be used to identify materials.

Sugar, salt, cornstarch, baking powder, baking soda, and alum can be compared using just our senses.

Sugar and cornstarch can be obtained from plants.

When sugar is dissolved in water, there is no change in weight.

Dissolving and evaporation can be explained by particles.

Solids can be compared based on how they mix with water.

A mixture of coconut oil and beeswax melts more easily than beeswax alone.

Mixtures have different melting points and freezing points from pure materials.

Solids can be compared based on how they respond to heat.

Bubbles or a change in color can be observed when six solids are mixed with vinegar or iodine.

Bubbles or a change in smell, color, or texture can be a sign that a new material has been made.

When something new is formed, there is no change in weight.

A model can be used to plan an investigation.

Unknown solids can be identified by comparing properties.

Scientists use evidence when communicating their findings.

Plants need many things to live and grow, but not all of them contribute most of the matter to growth.

Plants take in carbon dioxide from the air, and air is made up of particles.

Air is matter, and light is energy.

Plants get most of their matter for growth from air and water, not soil.

Animals need matter and energy to live and grow, and to gain weight they need to consume more food.

Food is a source of energy for animals.

Animals get both the matter and the energy they need from food.

Organisms are related in food webs, which can be used to model the flow of matter and energy.

Decomposers return matter from dead organisms to the environment.

Energy flows and matter cycles through living and nonliving components of ecosystems.

Organisms can survive only in environments in which their needs for matter and energy are met.

Newly introduced species can often cause problems in native ecosystems.

The introduction of a top predator can sometimes have a cascade effect that reaches the bottom of the food web.

Sea squirts often hitchhike on boats and become invasive species.

Models can be used to make predictions about locations that are more susceptible to invasion.