Mid-Ocean Ridges
What long, elevated feature circles the Earth under the oceans and is the site of many earthquakes and volcanic eruptions?
Mid-Ocean Ridge
What is the name of the process where new ocean crust forms at mid-ocean ridges and pushes older rock aside?
Sea-Floor Spreading
On the chart, does the age of sea-floor rocks increase or decrease with distance from the ridge?
Increase
What are the giant slabs of Earth's surface called that move slowly on the mantle?
Tectonic Plates
Define "rift" as used in the sea-floor spreading diagrams.
A crack or valley at the center of the ridge where magma rises (a rift)
About how long is the mid-ocean ridge system that circles the Earth (approximate, in km)?
about 60 000 km
What does molten rock do at a rift to create new oceanic crust?
It rises as magma into the rift, cools, and hardens to form new crust
What technology from the 1970s gave scientists direct photographic evidence of the ocean floor and sea-floor spreading?
ROVs (remote operated vehicles) with cameras
About how fast do tectonic plates move per year? Give the approximate rate and a familiar comparison from the text.
about 2.5 cm per year - about he rate fingernails grow
What is a "deep-sea trench"? Give one example named in the text.
A long, narrow deep depression in the ocean floor; example: Mariana Trench
Name one feature found on the ocean floor that is as high as some mountain ranges on land.
Mid-Ocean Ridges
According to the diagram and data, how does the thickness of sediment change as you move away from a mid-ocean ridge?
Sediment gets thicker as you move away from the ridge (thin near ridge, thicker farther away)
Name two types of ocean-floor features discovered by sound-wave mapping that are important evidence for plate tectonics.
Mid-Ocean ridges and deep-sea trenches
How many major plates are mentioned in the text?
12 major plates
What does "ROV" stand for and give one way ROVs help scientists study plate tectonics.
Remote Operated Vehicle; ROVs take photos, video, and samples to observe seafloor features directly
Why do scientists think mountain ranges form both on land and on the ocean floor?
Because both have mountain-building processes from rising molten rock and tectonic activity; evidence: ridges, volcanoes, and earthquakes found in both places
Using the example on the chart, approximately how far from the Mid-Atlantic Ridge are rocks that are 60 million years old?
~1200 km from the Mid-Atlantic Ridge (text: 60 million years at 1200 km)
Say a simple sentence relating rock age to distance from the Mid-Atlantic Ridge based on the scatter plot trend.
"As distance from the Mid-Atlantic Ridge increases, the age of the seafloor rocks increases."
If the North American Plate moves at about 2.5 cm per year, how far would it move in 10 years?
25 cm
Explain the meaning of "young rocks" vs. "old rocks" in the ocean-floor diagrams — what evidence tells us which is which?
"Young rocks" are nearer the ridge with thinner sediment cover; "old rocks" are farther with thicker sediment — evidence: sediment thickness and radiometric/age data from samples
Describe two observations made with early ocean mapping (weighted ropes, sound waves) that helped reveal mid-ocean ridges and trenches.
Early weighted ropes measured depth; later sonar/sound-wave mapping revealed mid-ocean ridges and deep trenches
Explain how sea-floor spreading provides a mechanism for continents to move. Include the conveyor-belt analogy from the text.
New crust forms at ridges and pushes older crust aside, carrying continents like objects on a conveyor belt
What two kinds of data together helped scientists develop the theory of plate tectonics?
Age/location data of rock samples + direct observations/photographs and mapping of ocean-floor structures
Describe how plate boundary activity at ridges and trenches relates to plate interactions (use the legend arrows concept: plates moving apart vs. together).
Ridges = divergent boundaries creating new crust; trenches = convergent boundaries where crust is consumed; arrows show directions of movement
Using the text, define "sea-floor spreading" in one clear sentence that includes the role of magma and ridge movement.
Sea-floor spreading: magma rises at mid-ocean ridges to form new oceanic crust that pushes older crust away, carrying continents