Introducing KNOVA — A free reading app with curriculum-aligned passages on History & Science for Grades 3-8Learn More →

Seafloor Spreading — Reading Comprehension

No ratings yet

Premium Resource

Grades

Standards

MS-ESS2-2
MS-ESS2-3

Rate this resource

Send Feedback / Report an Issue

About This Reader

This comprehensive passage introduces middle school students to the concept of seafloor spreading, a fundamental process shaping Earth's surface. Aligned with NGSS standards MS-ESS2-2 and MS-ESS2-3, it details Harry Hess's groundbreaking discovery in the 1960s, explaining how new oceanic crust forms at mid-ocean ridges and is gradually pushed outward, providing the missing mechanism for continental drift. Students will learn about the role of magma, the significance of magnetic striping, and the importance of deep ocean trenches. The passage emphasizes systems thinking, cause-and-effect relationships, and the scientific evidence supporting these ideas. Activities include a glossary, differentiated reading, Spanish translations, quizzes, writing prompts, and graphic organizers for critical thinking and comprehension. Integrated audio tools are available for diverse learners. This resource is ideal for teaching plate tectonics and Earth's dynamic processes in an engaging, standards-based format.

CONTENT PREVIEW

seafloor-spreading-2 — Diagram of the seafloor spreading process

Seafloor spreading is the process that forms new oceanic crust at underwater mountain chains called mid-ocean ridges. This process is important because it explains how continents can move over time and why the ocean floor looks the way it does. In the 1960s, geologist Harry Hess studied the patterns of the ocean floor and provided key evidence for how Earth's surface changes. His discovery helped solve the mystery of continental drift, a theory that continents have shifted positions over millions of years.

How New Seafloor Forms

At the center of the world's oceans, vast mid-ocean ridges stretch for thousands of kilometers. At these ridges, magma from Earth's mantle rises upward through cracks in the oceanic crust. As the magma reaches the surface, it cools and hardens to form new crust. This new crust gradually pushes the older crust away from the ridge at a rate of about 2 to 10 centimeters per year. The youngest rocks are found closest to the ridge, while older rocks lie farther away. This movement is a key part of plate tectonics, the scientific theory explaining the movement of Earth's plates.

Evidence for Seafloor Spreading

Scientists found two main types of evidence for seafloor spreading. First, drilling samples revealed that the age of the oceanic crust increases with distance from the mid-ocean ridge. The rocks at the ridge are only a few million years old, while those near deep ocean trenches can be over 180 million years old. Second, rocks on either side of the ridge show a pattern of magnetic striping. When magma cools, magnetic minerals inside the rock align with Earth's magnetic field. Over time, Earth's magnetic field has reversed many times. This creates alternating bands of normal and reversed magnetic orientation, which appear as stripes that are symmetrical on both sides of the ridge. This symmetry provides strong evidence that new crust forms at the ridge and moves outward equally in both directions.

Destruction of Oceanic Crust

As new crust forms and moves away from the mid-ocean ridge, it eventually reaches a deep ocean trench. Here, the oceanic crust sinks back into the mantle in a process called subduction. This recycling of crust means that Earth's surface is always changing, with old crust being destroyed and new crust being created. Seafloor spreading and subduction are both crucial to the theory of plate tectonics. They help explain earthquakes, volcanic activity, and the movement of continents.

Seafloor spreading has transformed our understanding of Earth's surface. By studying ocean floors, scientists can track plate movement, predict geological events, and learn more about our planet's history. The process also connects to larger scientific ideas about cycles, energy flow, and the dynamic nature of Earth's systems.

Interesting Fact: The entire Atlantic Ocean floor is less than 200 million years old, while some continental rocks are over 4 billion years old!

What is seafloor spreading?

The creation of new oceanic crust at mid-ocean ridgesThe sinking of continents into the oceanThe movement of magma deep in the coreThe shifting of Earth's magnetic field

Who provided key evidence for seafloor spreading in the 1960s?

Isaac NewtonCharles DarwinHarry HessMarie Curie

Where are the youngest oceanic rocks found?

Close to deep ocean trenchesNear the mid-ocean ridgeAt the bottom of the mantleOn the continents

What happens to old oceanic crust at deep ocean trenches?

It is pushed upward to form mountainsIt sinks back into the mantleIt floats to the surfaceIt turns into magma immediately

What is the meaning of 'magnetic striping' as used in the passage?

Patterns of alternating magnetic direction in oceanic rocksLines painted by scientists on the ocean floorStripes caused by ocean currentsRocks that are only found above water

What does 'symmetry' mean in the context of seafloor spreading?

A balanced pattern of magnetic stripes on both sides of the ridgeRocks that are exactly the same everywhereThe way continents fit togetherEqual temperatures in the ocean

Why is seafloor spreading important for understanding earthquakes?

It shows how earthquakes are caused by the movement of oceanic crustIt proves earthquakes only happen in oceansIt explains why the ocean is saltyIt prevents earthquakes from happening

If oceanic crust is constantly created and destroyed, what does this suggest about Earth's surface?

Earth's surface is always changingEarth's surface never changesOceans are shrinking over timeContinents are made of new crust

True or False: The rocks at the mid-ocean ridge are among the oldest on Earth.

TrueFalse

True or False: Subduction is the process where one tectonic plate sinks beneath another.

TrueFalse