4.5 - EXERCISES

Today, we are going to discuss the concept of continental drift. Can anyone tell me who first proposed this idea?

Exactly! Wegener introduced this theory in 1912, proposing that continents were once part of a supercontinent called Pangaea.

Pangaea means 'all earth'. It suggests that all continents were combined into one large landmass.

He suggested forces like the polar-fleeing force caused by Earth's rotation. Let's remember it as 'P-FORCE' for quick recall.

Great question! Evidence, such as the matching coastlines of South America and Africa and fossils found on various continents, support his theory.

To summarize, Wegener's theory of continental drift proposed that continents were once connected. Evidence includes coastlines fitting together and similar fossils across oceans.

Now that we understand continental drift, let’s delve into plate tectonics. Who can explain what plate tectonics is?

Absolutely! The Earth's lithosphere is divided into several plates that move over the mantle. This movement is driven by convection currents.

Convection currents are caused by heat from radioactive decay in the mantle, causing a cycle of rising and sinking materials. Remember 'HEAT CYCLE' to recall why they move!

Exactly! Most seismic activities occur along plate boundaries. They can either converge, diverge, or transform. Let’s keep 'THE THREE C'S' in mind—Convergent, Divergent, and Transform!

In summary, plate tectonics involves lithospheric plates moving due to convection currents, which leads to geological events like earthquakes and volcanic eruptions.

Let’s examine the evidence supporting continental drift and plate tectonics. What types of evidence do we have?

Absolutely! Identical fossils found on continents separated by oceans, such as Mesosaurus in South America and Africa, challenge the idea of separate development.

Excellent point! Matching geological formations and age of rocks across continents suggest they were once joined. Let's memorize 'MATCHING ROCKS' for this evidence.

Right! Tillites found in different southern continents suggest a shared glacial past, indicating they were much closer together during their formation.

In summary, geological evidence, fossil distribution, and glacial deposits collectively support the theory of continental drift and plate tectonics.

Let’s talk about sea floor spreading. What happens at the mid-ocean ridges?

Exactly! As magma rises from the mantle and cools, it creates new crust. This process is key in the theory of sea floor spreading.

Great question! Old oceanic crust is pushed down into trenches and recycled, which we can remember as 'RECYCLE CRUST'.

Good observation! Magnetic stripes on either side of the ridge and the age of rocks support the idea. Younger rocks at the ridge, older as you move away.

In summary, sea floor spreading at mid-ocean ridges creates new crust, older crust is subducted, and magnetic evidence helps track this process.