earth science stem 11 how sea floor spreads

spreading of sea floor

1. HOW SEafloor spreads? S E AF L OOR S P READING

2. R N A O S Let's play a game!  2 pics 1 word

3. S R O A N

4. S A O E O F L R

5. S O E O A F L R

6. C E O N A

7. O N C A E

8. SEAFL OOR SPREADING OBJECTIVES:                        Sea-floor Spreading  

9. Seafloor Spreading is the process in which the ocean floor is extended when two plates move apart.              

10. As magma seeps out between two plates, it solidifies and extends the ocean floor and creates a long chain mountain called the  Mid-Oceanic Ridge.

11. SEAFL OOR SPREADING Seafloor spreading is the movement of two oceanic plates away from each other (at a divergent plate boundary), which results in the formation of new oceanic crust (from magma that comes from within the Earth's mantle) along a mid-ocean ridge. When the oceanic plates are moving away from each other it is called a Zone of Divergence.

12. S E AF L OOR S P READING Seafloor Spreading Hypothesis Proposed by Harry H. Hess in 1960, he hypothesized that the formation of underwater mountains and new ocean floors were caused by the Earth's mantle rising up between two plates.

13. S E AF L OOR S P READING The world's ocean floor are spreading outward from the mid-ocean ridges at a geographically varying rate of 1 to 2 inches per year and then subducting under the less dense continental plates, destroying old crust at roughly the same rate as the rifts are creating new crust.

14. The boundaries where the plates move apart are 'constructive' because new crust is being formed and added to the ocean floor. The ocean floor gradually extends and thus the size of the plates increases.

15. As these plates get bigger, others become smaller as they melt back into the Earth in the process called Subduction.  Subduction is a geological process in which the oceanic lithosphere and some continent lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates.   Where one tectonic plate converges with a second plate, the heavier plate dives beneath the other and sinks into mantle.

16. Sonar – a device that bounces sound waves off underwater objects and then records the echoes of these sounds waves. The time it takes for the echo to arrive indicates the distance to the object.

17. S E AF L OOR S P READING Supporting Evidence for Seafloor Spreading 1. Molten material 2. Drilling samples 3. Magnetic stripes

18. At the mid-ocean ridge, molten material rises up from the mantle and spreads out, pushing the older rocks to both sides of the ridge.

19. Rock shaped like pillows (rock pillows) show that molten material  has erupted again and again from cracks along the mid-ocean ridge and cooled quickly.

20. Evidences from Drilling Samples Samples of the deep ocean floor show that basaltic oceanic crust and overlying sediment become progressively younger as the mid-ocean ridge is approached, and the sediment cover is thinner near the ridge. The rock making up the ocean floor is considerably younger than the continents, with no samples found over 200 million years old, as contrasted with maximum ages of 3 billion years for the continental rocks. This confirms that older ocean crust has been reabsorbed in ocean trench systems. 

21. S E AF L OOR S P READING Evidence from Magnetic Stripes By the mid-1960s studies of the earth's magnetic field showed a history of periodic reversals of polarity. The magnetic history of the earth is thus recorded in the spreading ocean floors as in a very slow magnetic tape recording, forming a continuous record of the movement of the ocean floors.

22. SEAFL OOR SPREADING Magnetic surveys conducted near the mid-ocean ridge showed elongated patterns of normal reverse and reversed polarity of the ocean floor in bands paralleling the rift and symmetrically distributed as mirror images on either side of it.

23. In conclusion, seafloor spreading is a process where new oceanic crust forms at mid-ocean ridges as tectonic plates move apart. Molten material from the mantle rises, cools, and solidifies, pushing older crust away and causing the seafloor to expand. This supports the theory of plate tectonics and explains continental drift. Key evidence includes magnetic patterns in oceanic rocks, the age distribution of the seafloor, and seismic activity along ridges. It is essential in understanding Earth's geological processes.

24. THANK YOU!