Evidence of Past Motion
This preserved remains or sign of an organism that lived long ago can help scientists study Earth’s past.
What is a fossil?
This boundary forms where two plates move apart.
What is a divergent boundary?
New ocean floor forms at these underwater features, where plates move apart.
What are mid-ocean ridges?
This is the place where two tectonic plates meet.
What is a plate boundary?
Scratches left by these can be found in parts of Africa and India that are warm today.
What are glaciers?
Fossils of this freshwater reptile have been found in both South America and Africa.
What is Mesosaurus?
At this boundary, plates slide past each other, often along faults.
What is a transform boundary?
This melted rock rises and cools to form new seafloor crust.
What is magma?
This is the process in which one plate sinks beneath another and moves into the mantle.
What is subduction?
At a transform boundary, plates move in this way.
What is they slide past each other?
Why do matching Mesosaurus fossils on two continents support the idea that those continents were once connected?
What is because a freshwater reptile was unlikely to cross a wide saltwater ocean?
Name one feature that can form where an oceanic plate sinks beneath a continental plate.
What is a deep ocean trench or volcanic mountains on the continent?
Why is oceanic crust near a mid-ocean ridge generally younger than crust farther away?
What is because new crust forms at the ridge and moves outward?
In mantle convection, warmer rock rises while this happens to cooler rock.
What is it, sinks?
What can form when magma rises and cools at a mid-ocean ridge?
What is new crust?
Similar rock layers and mountain belts along the coasts of South America and Africa may be evidence of this.
What are features that formed while the continents were connected?
When two continental plates push together, the crust can thicken and form these.
What are high fold mountains?
Matching magnetic stripes on both sides of a ridge support this process.
What is seafloor spreading?
Describe how mantle convection can help move tectonic plates.
What is warmer mantle rock rises and spreads beneath plates, then cools and sinks, helping move the plates above?
Compare a divergent boundary with an ocean–continent convergent boundary. Name one feature at each.
What is plates move apart and can form a ridge or rift valley; at an ocean–continent convergent boundary, one plate sinks beneath another and can form a trench or volcanic mountains?
Why is using several kinds of evidence stronger than relying on one clue about past plate motion?
What is because different clues can support the same explanation, while one clue may have other possible explanations?
Explain why earthquakes and volcanoes are common along many plate boundaries.
What is because plates push, pull, or slide against rock, and some interactions allow magma to form and rise?
Why is the oldest ocean floor much younger than some continental rocks?
What is because old oceanic crust sinks back into the mantle at subduction zones and is recycled?
Mantle rock is solid, but it can do this slowly over long periods.
What is flow?
Explain how magnetic stripes on both sides of a mid-ocean ridge show that seafloor formed there and moved outward.
The matching stripe patterns and ages on both sides suggest that new seafloor formed at the ridge and spread away in both directions.