Continental Drift What’s the big idea?

What will you learn? In science, a new idea has the power to change everything we thought we knew about our world. But how do scientists prove that their new ideas are correct? Here are the big ideas you will learn about in this lesson: The continents are in slow but constant motion, riding on top of pieces of Earth's crust called tectonic plates The scientific community often refuses to accept new scientific theories that challenge existing ones Scientists often use new evidence to build on other scientists’ work and strengthen theories

Vocabulary Continent Evidence Fossil Geologist Theory Continental drift Plate tectonics

Scientific Theory/Model Evidence and theories Scientists collect evidence, including objects they have found and things they have observed, as part of their research. Based on this evidence, they come up with a theory that explains how something occurs—or has occurred—in the natural world. Scientific Theory/Model Analysis Records Insight Data Experiments

Continental Drift Theory Scientists use theories to explain everything from how the universe began to why objects fall to the ground. In 1915, German scientist Alfred Wegener published a book to present a theory he called "continental drift." Wegener believed that the large pieces of land we call continents move over long periods of time.

Evidence to support continental drift Shape similarity Fossils Glacial and Coal Deposits Similarity of rocks and mountains

Shape similarity – the coasts of South America and Africa join almost like a jigsaw puzzle Fossils – plant and animal fossils are found on different that are now very far apart

Similarity of rocks and mountains across continents Glacial striations and coal deposits in areas that are now areas that would not support them

Continental Drift Activity Instructions: On the puzzle pieces handout, assign a colour to each type of fossil or mountain belt in the legend – colour the areas of the landmasses according to the legend Use scissors to cut along borders of the continents Place the continents on new page in your book and move them around using the fossil and mountain chain evidence to match NOTE: The pieces may not fit exactly! Once assembled, glue the continents into your book in the shape of the supercontinent. Glue in the legend to your puzzle.

Plate tectonics The evidence needed to support Wegener’s theory

What did we learn last lesson? The continents are in slow but constant motion, riding on top of pieces of Earth's crust called tectonic plates The scientific community often refuses to accept new scientific theories that challenge existing ones Scientists often use new evidence to build on other scientists’ work and strengthen theories

Plate tectonics

Plate tectonics – boundary interactions The edges of the tectonic plates are called plate boundaries, and events such as earthquakes, volcanoes and tsunamis originate at these narrow boundary zones between the plates. Different type of interactions occur between plates as they move around, producing different types of earthquakes and volcanos. Plates may pull apart, collide, or scrape past each other.

Divergent Plates moving apart produce a divergent plate boundary. Almost all of the Earth's new crust forms at divergent boundaries. When the plates move away from each other the magma from the mantle rises up and forces its way to the surface in a lava flow, where it solidifies as new crust. Many divergent plate margins are under the oceans, creating long undersea rift zones that fill with lava - called mid-ocean ridges.

Seafloor Spreading – samples of ocean floor are youngest close to the ridge, and older as you move further away. In other words, new crust is created at mid-ocean ridges and spreads out World map showing mid-ocean ridges

Convergent Plates pushing against each other or are colliding produce a convergent plate boundary. This type of boundary results in one plate is being pulled beneath another (subduction) forming a deep trench. The long, narrow zone where the two plates meet is called the subduction zone. The more dense oceanic crust is being subducted under the less dense continental crust. Subduction zones tend to create large, cone-shaped volcanoes.

Transform A transform plate boundary occurs where one plate grinds past another, side by side. An example of this type of boundary occurs off the west coast of California, and separates the Pacific plate from the North American plate along the San Andreas fault - a famous plate that is responsible for many of California's earthquakes.

Vocabulary – write a definition for each, and what happens at each boundary Plate tectonics Fault Divergent Convergent Transform