Types of Plate Boundaries — Reading Comprehension

Earth's surface is like a giant jigsaw puzzle, with tectonic plates constantly moving and interacting. Geologists piece together clues from rocks, fossils, and seafloor structures to map ancient plate boundaries and understand how our planet has changed over millions of years.

1. Divergent Boundaries: Pulling Apart

Evidence:

●       Pillow basalts: Lava that cools rapidly underwater, forming bulbous shapes (common at mid-ocean ridges).

●       Magnetic stripes: Symmetrical patterns of magnetic minerals in seafloor rock, recording Earth's magnetic field reversals as new crust forms.

●       Fossil clues: Identical freshwater reptile fossils (like Mesosaurus) found in Africa and South America—continents now separated by the Atlantic Ocean.

Example: The Mid-Atlantic Ridge shows young, basaltic rock at the center, aging outward—proof of seafloor spreading.

2. Convergent Boundaries: Colliding Plates

Evidence:

●       Ophiolites: Slabs of ancient oceanic crust thrust onto continents (e.g., California's Coast Ranges).

●       Metamorphic rocks: High-pressure minerals like blueschist form where plates subduct.

●       Fossil mismatches: Marine fossils atop mountains (Himalayas) reveal landmasses once underwater.

Example: The Andes Mountains contain volcanic rocks and folded sedimentary layers, showing oceanic-continental collision.

3. Transform Boundaries: Sliding Past

Evidence:

●       Offset features: Rivers or rock layers abruptly cut by faults (like California's San Andreas).

●       Earthquake scars: Pulverized rock ("fault gouge") along shear zones.

Example: The Alpine Fault in New Zealand has shifted rocks 480 km horizontally over 25 million years!

Putting It All Together

By studying:

●       Rock ages (youngest at divergent zones, oldest near trenches),

●       Fossil distributions (like tropical plant fossils in Arctic rocks),

●       Magnetic and seismic data,

scientists reconstruct Earth's "lost" boundaries—like the ancient Tethys Ocean floor now crumpled into the Himalayas

Fun Fact: The same dinosaur species (Plateosaurus) fossils found in Europe and North America prove these continents were once connected!

Another Fun Fact: Did you know that the Himalayas contain fossilized seashells and shark teeth? These marine fossils, found at the top of Mount Everest, prove that the world's highest mountain range was once the bottom of an ancient ocean! This incredible transformation happened when India crashed into Asia 50 million years ago at a 

What type of rock forms when lava cools rapidly underwater at divergent boundaries?

Why are identical freshwater reptile fossils found on different continents?

What creates the symmetrical magnetic stripes on the seafloor?

What happens to oceanic crust at convergent boundaries?

What type of boundary would you expect to find offset rivers or rock layers?

What kind of fossils would you most likely find on top of the Himalayas?

What does the presence of ophiolites on continents suggest?

How do scientists use rock ages to study plate boundaries?