SmartBook: Seafloor Spreading

An imaginary line on a map that shows points that have the same age is called a(n)

isochron

What is an imaginary line on a map that shows points that have the same age?

isochron

What did scientists learn by matching magnetic patterns on the seafloor with known patterns of magnetic reversals on land?

the age of the ocean floor

Place the steps in the process of seafloor spreading in proper order.

1. Magma is forced toward the surface of the crust along an ocean ridge. 2. Two sides of the ridge spread apart and rising magma fills the gap that is created. 3. Magma solidifies into a small amount of new ocean floor. 4. The cycle of spreading and solidifying continues, forming new ocean floor that slowly moves away from the ridge.

During seafloor spreading, ____ is forced up to the crust along an ocean ridge. The ____ spreads apart, and the rising magma fills the gap and solidifies into ocean floor. The process continues, forming new ____ floor that slowly moves away from the ridge.

Blank 1: magma Blank 2: ridge Blank 3: ocean

By matching magnetic patterns on the seafloor with known patterns of ____ reversals on land, scientists were able to determine the ____ of the ocean floor. They found that rocks are younger near ____ ridges and older near deep-sea ____.

Blank 1: magnetic Blank 2: age Blank 3: ocean or mid-ocean Blank 4: trenches

What rock evidence led to the discovery of seafloor spreading?

The oldest oceanic rocks are much younger than the oldest continental rocks. The age of oceanic crust consistently increases with distance from a ridge. The thickness of ocean sediments increases with distance from an ocean ridge.

Which major ocean-floor features were discovered by data collected by sonar and magnetometers?

deep-sea trenches ocean ridges

What happens when the flow in the outer core changes, and Earth's magnetic field changes direction?

magnetic reversal

What device can detect small changes in magnetic fields?

magnetometer

Which technological advances in the 1940s and 1950s changed how scientists viewed the ocean floor?

magnetometer sonar

What theory explains how new oceanic crust is formed at ocean ridges, slowly moves away from ocean ridges, and is destroyed at deep-sea trenches?

seafloor spreading

What is true of magnetic fields?

A magnetic field with normal polarity has the same orientation as Earth's present field. A magnetic field with reversed polarity has the opposite orientation as Earth's present field.

A ____ ____ happens when the flow in the outer core changes, and Earth's magnetic field changes direction.

Blank 1: magnetic Blank 2: reversal

A device that can detect small changes in magnetic fields is called a(n)

Blank 1: magnetometer

A magnetic field that has the same orientation as Earth's present field has ____ polarity. A magnetic field that is opposite to the present field has ____ polarity.

Blank 1: normal Blank 2: reversed

The theory that explains how new oceanic crust is formed at ocean ridges, slowly moves away from ocean ridges, and is destroyed at deep-sea trenches is called ____ ____.

Blank 1: seafloor Blank 2: spreading

Technologies that changed perceptions of the ocean floor include ____, which measures water depth and maps the ocean floor, and the ____, which records the magnetic field generated by ocean floor rocks.

Blank 1: sonar Blank 2: magnetometer

Two major ocean-floor features discovered by data collected by ____ and magnetometers include underwater mountain chains, called ocean ____, and deep-sea ____.

Blank 1: sonar Blank 2: ridges Blank 3: trenches

What sediment evidence led to the discovery of seafloor spreading?

Layers of sediments on the ocean floor are much thinner than layers of sediment on continents.

The study of the history of Earth's magnetic field is called

paleomagnetism

What is the study of the history of Earth's magnetic field?

paleomagnetism