Science 10: Lesson 5 Seafloor Spreading
Summary
TLDRIn this science lesson, Marian Soriano revisits the continental drift theory, explaining how continents once formed a single landmass called Pangaea and later split into Laurasia and Gondwanaland. She introduces Alfred Wegener's evidence for continental drift, including matching continental shapes and fossil records. The lesson then delves into the concept of seafloor spreading, a key process supporting continental drift, which involves the creation of new oceanic crust at mid-ocean ridges and its subsequent movement away from the ridge. Evidence for seafloor spreading includes the age and density of rocks, sediment thickness, and geomagnetic reversal patterns. The lesson concludes by emphasizing the balance between crust creation and destruction, maintaining Earth's shape and size.
Takeaways
- 🌏 The continental drift theory suggests that continents were once part of a single landmass called Pangaea, which later split into Laurasia and Gondwanaland.
- 🔍 Alfred Wegener proposed the continental drift theory, citing evidence such as matching continental shapes, fossil records, and ancient climates.
- 🚫 Despite the evidence, Wegener's theory was initially rejected due to a lack of a mechanism to explain how continents could drift.
- 🌊 Seafloor spreading was introduced as a concept by Harry Hess, who used sonar technology to study the ocean floor and its relation to continental drift.
- 🔥 Seafloor spreading theory posits that new oceanic crust is formed at mid-ocean ridges as magma rises and spreads sideways, creating new sea floor.
- 📏 Evidence for seafloor spreading includes the finding that the youngest rocks are near the ridges, while the oldest are found further away.
- 🌌 The ages, densities, and thicknesses of the oceanic crust increase with distance from the mid-ocean ridges.
- 🧲 Geomagnetic reversals provide strong evidence for seafloor spreading, with matching magnetic stripes on either side of mid-ocean ridges indicating past magnetic field changes.
- 🌍 Seafloor spreading disproves the idea that continents move through static oceans, showing that oceans are also sites of tectonic activity.
- ⚖️ The balance between seafloor spreading, which creates new crust, and subduction, which destroys old crust, maintains the Earth's shape and size.
- 📚 The lesson concludes that seafloor spreading occurs at divergent plate boundaries and is a key process in understanding the Earth's tectonic movements.
Q & A
What is the Continental Drift Theory?
-The Continental Drift Theory, proposed by Alfred Wegener, suggests that continents are slowly drifting around the Earth and were once part of a single large landmass called Pangaea.
What were the two supercontinents formed after the division of Pangaea?
-After the division of Pangaea, the supercontinent split into two parts: Laurasia, which drifted to the north, and Gondwanaland, which drifted to the south.
What evidence did Alfred Wegener identify to support the Continental Drift Theory?
-Wegener identified several pieces of evidence, including the matching shapes of continental edges, fossil evidence, cold deposits in Antarctica, ancient climates, and glacier carvings.
Why was the Continental Drift Theory initially rejected?
-The theory was initially rejected because Wegener could not explain the mechanism causing the continents to drift.
What is Seafloor Spreading?
-Seafloor Spreading is a geological process where new oceanic crust is formed at mid-ocean ridges as magma rises, cools, and solidifies, pushing older crust away from the ridge.
Who was Harry Hammond Hess and what was his contribution to the understanding of the ocean floor?
-Harry Hammond Hess was a professor of geology at Princeton University who used sonar to study the ocean floor during World War II. He is known for developing the idea of seafloor spreading.
What evidence supports the idea of seafloor spreading?
-Evidence supporting seafloor spreading includes the presence of the youngest rocks near the ridge, progressively older rocks as one moves away from the ridge, thinner sediments near the ridge, and symmetrical magnetic stripes on either side of the mid-ocean ridges.
How do the ages, densities, and thicknesses of the oceanic crust relate to the mid-ocean ridge?
-The ages, densities, and thicknesses of the oceanic crust increase with distance from the mid-ocean ridge, indicating that new crust is being created at the ridge.
What is the relationship between seafloor spreading and geomagnetic reversal?
-Geomagnetic reversal is a phenomenon that provides evidence for seafloor spreading. The magnetism of the ocean floor, recorded in the basalt rock, shows symmetrical stripes on either side of the mid-ocean ridges, indicating past reversals of the Earth's magnetic field.
How does seafloor spreading disprove and support the Continental Drift Theory?
-Seafloor spreading disproves the original idea that continents move through unmoving oceans. It supports the Continental Drift Theory by showing that the ocean floor is an active site of tectonic activity, with new crust being created and old crust being destroyed through subduction.
How do seafloor spreading and subduction maintain the shape and diameter of the Earth?
-Seafloor spreading creates new crust, while subduction destroys old crust. These two processes roughly balance each other, keeping the shape and diameter of the Earth constant.
Outlines
🌏 Continental Drift and Seafloor Spreading Theories
This paragraph introduces the concept of continental drift, which posits that continents were once part of a supercontinent called Pangaea and have since drifted apart to form the current continents. The theory was proposed by Alfred Wegener and supported by evidence such as matching continental shapes, fossils, and geological features. Despite this, the theory was initially rejected due to a lack of a mechanism for the drift. The paragraph also introduces the concept of seafloor spreading, which was developed as a result of sonar technology in the 1930s and further supported continental drift by explaining the movement of tectonic plates and the creation of new oceanic crust at mid-ocean ridges.
🌊 Seafloor Spreading and Subduction: Balancing Earth's Crust
The second paragraph delves into the specifics of seafloor spreading, detailing how new oceanic crust is formed at divergent plate boundaries and how the process is evidenced by the distribution of rock ages and sediment thickness near the ridges. It also discusses the concept of subduction, where old crust is destroyed, and how these two processes maintain the Earth's shape and size. The paragraph concludes with a summary of the key points about seafloor spreading and its implications for understanding the Earth's geological activity, as taught by Marianne Zoriano.
Mindmap
Keywords
💡Continental Drift Theory
💡Pangaea
💡Laurasia
💡Gondwanaland
💡Seafloor Spreading
💡Mid-Ocean Ridge
💡Magma
💡Subduction
💡Geomagnetic Reversal
💡Basalt
💡Tectonic Plates
Highlights
Continental drift theory posits that continents slowly drift around the Earth.
Pangaea was once a large landmass that divided into Laurasia and Gondwanaland.
Alfred Wegener's evidence for continental drift includes matching continental edges and fossil evidence.
Seafloor spreading was discovered with the development of sonar technology in the 1930s.
Harry Hess's studies on the mid-ocean ridge system led to the concept of seafloor spreading.
Seafloor spreading involves hot material rising and creating new sea floor at the mid-ocean ridge.
Evidence for seafloor spreading includes the youngest rocks being found near the ridge.
Oldest rocks and thicker sediments are found further from the mid-ocean ridge.
Geomagnetic reversals provide strong evidence for seafloor spreading.
Basalt's magnetism records the Earth's magnetic field as it cools, forming symmetrical stripes.
Seafloor spreading disproves the idea of continents moving through static oceans.
Seafloor spreading and subduction balance each other, maintaining Earth's shape and diameter.
Subduction destroys old crust, balancing the creation of new crust by seafloor spreading.
The process of seafloor spreading occurs at divergent plate boundaries.
The density of oceanic crust increases with distance from the mid-ocean ridge.
Seafloor spreading is a key geological process that shapes the Earth's crust.
Teacher Marian Soriano concludes the lesson on seafloor spreading and its implications for continental drift.
Transcripts
hello students welcome to great and
science lessons
and i'm your teacher mom marian soriano
in our previous lesson you have learned
about continental drift theory
according to this theory continents are
slowly drifting around the earth and was
once a large landmass called panjaya
this supercontinent pangea was divided
into two super continents
named orisha and gondwanalan
pieces of lorasia drifted to the north
while pieces of ganduanolan drifted to
the south
and eventually drifted into day seven
continents
alfred wegener the originator of the
continental drift theory
identified several evidence to support
his claim
that continents are drifting
these evidence are shapes or matching
edges of continents or rocks
fossil evidence cold deposits in
antarctica
ancient climates and glacier carvings
despite of this evidence the continental
drift theory was still rejected
during begganer's time because he can't
explain
what causing the continents to drift
what other evidence can be used to
support the idea
that continents are drifting
let's find out in today's lesson
seafloor spreading
many people in the past believe that the
ocean floor is flat
like the desert
but in 1930s where sounding gear called
sonar was developed
leads to the discovery of the standing
feature of the ocean floor
one of the scientists to use sonar to
study ocean floor during world war
ii was harry hammond hesse a professor
of geology
at princeton university harry hess and
his team carefully examined maps of the
mid-ocean ridge system
then hes begun to think about the ocean
floor in relation to the problem of the
continental drift theory
that leads him to the idea of seafloor
spreading
according to the sea floor spreading
theory
hot less dense material below the
earth's crust rises towards the mid
ocean ridge this material flows sideways
carrying the seafloor away from the
reach and creates a crack in the crust
the magma flows out of the crack cools
down
and becomes a new sea floor over time
the new oceanic crust pushed the old
oceanic crust
far from the ridge and subducted
the idea of seafloor spreading is
supported by these evidence
find out that youngest rocks are found
near the ridge
while oldest rocks are found far from
the ridge
this provides evidence that seafloor
spreading and new crust is being created
at the reach
since there's spreading happening at the
ridge the sediments near the reach are
thinner
and progressively thickens as you move
away
always remember that the ages density
and thickness of the oceanic crust
increases with distance from the mid
ocean ridge
another strong evidence that supports
seafloor spreading is the geomagnetic
reversal
basalt the once molten rock that makes
up most new oceanic crust
is a fairly magnetic substance
scientists began using magnetometers to
measure the magnetism of the ocean floor
in the 1950s
scientists discovered that the magnetism
of the ocean floor around mid-ocean
ridges
was divided into matching stripes on
either side of the ridge
[Music]
the specific magnetism of basalt rock is
determined by the earth's magnetic field
when the magma
is cooling
scientists determined that the same
process formed the perfectly symmetrical
stripes on both sides of a mid-ocean
ridge
the continual process of seafloor
spreading separated the stripes in an
orderly pattern
how is seafloor spreading disproves and
supports continental drift theory
supporters of continental drift
originally theorized that the continents
move through unmoving oceans
seafloor spreading proves that the ocean
itself is a site of tectonic
activity
did you know that seafloor spreading and
subduction keeps the shape of the earth
seafloor spreading creates new grass
while subduction destroys old crust
the two forces roughly balance each
other so the shape and diameter of the
earth
remain constant
to summarize what you have learned
seafloor spreading
is a geologic process in which tectonic
plates split apart from each other
seafloor spreading occurs at divergent
plate boundaries
the evidence of sea floor spreading are
youngest rocks are found near the ridge
all these rocks are found far from the
reach
sediments are thinner near the reach and
progressively thickens as you move away
the density of materials increases as
you go far from the reach
symmetrical stripes on both sides of a
mid-ocean reach you also learn
that seafloor spreading creates new
crust while subduction destroys old
crust
the two forces roughly balance each
other so the shape and diameter of the
earth remain constant
i hope you learned and enjoyed our
lesson this is my marianne zoriano
see you in our next lesson
[Music]
you
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