Earth’s Interior Layers and Continental Drift

Objectives Review Earth’s layers Summarize Wegener’s hypothesis Describe the process of sea-floor spreading Identify how paleomagnetism provides support for the idea of sea-floor spreading Explain how sea-floor spreading provides a mechanism for continental drift.

Earth’s Interior: Physical properties

Based on Composition (What each layer is made of) Crust – solid, relatively low density silicate rock Mantle – Semi fluid, denser, mafic (iron and magnesium bearing) rocks Core – Liquid then solid iron and nickel with traces of heavier elements

Based on Structure(physical properties) Lithosphere – rigid Aesthenosphere – plastic Mesosphere – rigid Outer core – liquid Inner core - rigid

Warm-Up Question What does continental drift mean?

Wegener’s Theory Alfred Wegener proposed a theory that continents can drift apart from one another and have done so in the past ….known as Continental Drift

claimed that present day continents once made up a single land mass or supercontinent …known as Pangaea

Evidence of Continental Drift 1.Coastline similarities

Evidence of Continental Drift 2.Fossils Similar plant and animal fossils found on both sides of Atlantic Ocean

Evidence of Continental Drift 3.Rock Formations Rocks and mountain ranges found in continents separated by oceans are identical

Evidence of Continental Drift 4.Climates Glacial rock/debris was found in areas that today have warm climates

Why was Wegener’s theory rejected? He could not come up with a proven reason for why the continents did move His theory was not accepted until when geologists had more technology to help them map the ocean floor

Mapping of the ocean floor Used sonar to do this

What was found on the ocean floor… 1.Trenches Long valleys found along the edge of ocean basins

What was found on the ocean floor… 2.Mid-Ocean Ridges Long chains of underwater mountains Usually have a rift valley located at the center

Mid-Atlantic Ridge

What was going on at the mid-ocean ridges? Sea-floor Spreading New ocean floor forms from cooling lava in the rift valleys The sea floor then slowly moves out underneath ocean Will eventually sink back into Earth’s mantle at trenches

Sea-Floor Spreading

Evidence of sea-floor spreading Age of the ocean floor Age of ocean floor increases as you move away from ridges

Evidence of sea-floor spreading Magnetic reversals

Understanding Magnetic Reversals

Lava cools, lithospheric igneous rock forms… Many igneous rocks contain the mineral magnetite and the element iron… This causes the rocks to be magnetized = grains align in the same direction as Earth’s magnetic field Geologists know when these reversals occurred, so they can determine the age of the ocean floor

Magnetic Symmetry Our final piece of evidence is the magnetic record of the ocean floor. This shows the pattern of reversal and we find a near perfect mirror image on opposing sides of the ridge

Summary Question What was the proof that was found that supported Wegener’s theory of continental drift?

Homework Read Page #’s 239 – 246 Answer Question #’s 1 - 8