The Soil Myth: Evidence from Mass
The soil myth: evidence from mass teaches Grade 5 students to use experimental data to challenge the assumption that plants grow by 'eating' soil. If plants built their mass from soil, a pot of soil should lose significant weight as a tree grows large — but experiments show the soil's weight barely changes. This evidence proves that soil is not the main source of a plant's mass. The heavy trunk of a tree must come from somewhere else entirely, setting up the discovery that air and water are the real ingredients. From Amplify Science (California) Grade 5, Chapter 2.
Key Concepts
It looks like plants are built from the soil they grow in, but looks can be deceiving. Experiments show that if you weigh a pot of soil before and after a tree grows huge, the soil's weight barely changes.
This is strong evidence that plants do not "eat" soil to grow. The soil provides small amounts of vitamins, but it is not the main source of the plant's weight. The heavy mass of a tree trunk comes from somewhere else entirely.
Common Questions
What does the soil weight experiment show?
If you weigh soil before and after growing a tree in it, the soil barely loses any weight, even though the tree gained enormous mass. This is evidence that the tree's mass did not come from the soil.
Why do people think plants grow by eating soil?
Plants are rooted in soil and appear to grow from it. It looks as though they consume the dirt around them, but this is a misconception. The visual connection misleads our intuition.
If a plant's mass doesn't come from soil, where does it come from?
Plants build their mass primarily from carbon dioxide (a gas in the air) and water, which they combine using sunlight energy through photosynthesis. Air and water are the real ingredients.
What does soil actually provide for plants if not mass?
Soil provides small amounts of minerals and nutrients (like nitrogen and phosphorus) that act like vitamins. These support plant health but do not account for the bulk of the plant's mass.
What is evidence in science?
Evidence is data from observations or experiments that supports or disproves a claim. The soil weight experiment provides evidence against the claim that plants grow by consuming soil.
What grade and chapter covers the soil myth?
Grade 5, Chapter 2 of Amplify Science (California): Why aren't the cecropia trees growing and thriving?