B.P. #5 Present state of earth is temporary - different in past, future B.P. #6 Rates and scale of earth change are difficult to comprehend – either too slow relative to human life, or too huge in scale to imagine Related to how old we think the earth is ---- Prior to late 18 th century – earth = young; unchanging 1790’s on = earth processes the same as today; implies old earth How old?? 4.55 billion years old

Implications of huge amount of time – (“deep time”) Events that occur so slowly as to seem unimportant become important. Given time, unlikely events WILL eventually occur.

B.P. #4 Materials move within each sphere and between spheres Plate tectonic cycle

Cycling of Earth Materials – Plate tectonic cycle KEY TO HOW THE EARTH WORKS - NEW IDEA (1960’s) 1.Historical background – What they knew in the early 1900’s Continents and ocean floors – are different Features of continents & forces that formed them Continental drift – (1915) Alfred Wegener Reaction to Wegener

Height of the earth’s surface - B A What are the most common elevations of the earth’s surface?

Height of the earth’s surface - the hypsographic curve B A What are the most common elevations of the earth’s surface? 4-6 km below sea level, 0-1 km above sea level

How does this fit with Big Points from last week? What is the elevation of the ocean crust relative to the continental crust? Why is the ocean water where it is? What is the density of the ocean crust relative to continental crust?

What is the elevation of the ocean crust relative to the continental crust? Lower Why is the ocean water where it is? Water fills in low areas What is the density of the ocean crust relative to continental crust? Ocean crust is more dense than continental crust - lower How does this fit with Big Points from last week?

Cycling of Earth Materials – Plate tectonic cycle KEY TO HOW THE EARTH WORKS - NEW IDEA (1960’s) 1.Historical background – What they knew in the early 1900’s Continents and ocean floors –different crusts Features of continents & forces that formed them Continental drift – (1915) Alfred Wegener Reaction to Wegener

1. Folded Mountains

Appalachian Mtns

When layers of rocks are laid down - they are horizontal

rocks in folded mountains

What has happened to the rocks in folded mountains? Folded - not horizontal What force caused this? yields

What has happened to the rocks in folded mountains? Folded - not horizontal What force caused this? yields Compression -

Folded mountains, Pennsylvania

2. Rift systems

b. Rift systems - Sea level Side view How can a valley be formed that is below sea level?

2. Rift systems - Sea level Side view How can a valley be formed that is below sea level? Not by river erosion - rivers run to ocean.. Are not lower than sea level. Force?

2. Rift systems - Sea level Side view How can a valley be formed that is below sea level? Not by river erosion - rivers run to ocean.. Are not lower than sea level. Force? Tension

Rift valley - water can’t drain to ocean (why?) and so evaporates leaving white salts (Death Valley, CA)

Basin and Range from space, rift system - forces? x X = Death Valley area of previous slide

~Canada ~central US This is a cross-section view. 3. craton

~Canada ~central US This is a cross-section view.

Red = Canadian shield

Questions about shield: -- Where were these rocks formed - folded not broken? -- How did they get to the surface? -- Why are they so old? -- Where do they go to find the oldest rocks on earth? -- Where is ours?

Questions about shield: -- Where were these rocks formed - folded not broken? Deep in earth -- How did they get to the surface? -- Why are they so old? -- Where do they go to find the oldest rocks on earth? -- Where is ours?

Questions about shield: -- Where were these rocks formed - folded not broken? Deep in earth -- How did they get to the surface? Overlying miles of rocks were eroded… then pushed up… isostasy -- Why are they so old? -- Where do they go to find the oldest rocks on earth? -- Where is ours?

Questions about shield: -- Where were these rocks formed - folded not broken? -- How did they get to the surface? -- Why are they so old? Takes long time for erosion and uplift.. -- Where do they go to find the oldest rocks on earth? -- Where is ours?

Questions about shield: -- Where were these rocks formed - folded not broken? -- How did they get to the surface? -- Why are they so old? Takes long time for erosion and uplift.. -- Where do they go to find the oldest rocks on earth? Shields -- there is a shield on every continent -- Where is ours?

Questions about shield: -- Where were these rocks formed - folded not broken? -- How did they get to the surface? -- Why are they so old? Takes long time for erosion and uplift.. -- Where do they go to find the oldest rocks on earth? Shields -- there is a shield on every continent -- Where is ours? In Canada - northern MI, north NY

~Canada ~central US This is a cross-section view. c. Craton - 2nd part = stable platform(covered shield)

Nashville - covered shield - horizontal sedimentary rocks

Covered Shield = Blue, yellow Green

Covered shield (platform) - note horizontal layers

Cycling of Earth Materials – Plate tectonic cycle KEY TO HOW THE EARTH WORKS - NEW IDEA (1960’s) 1.Historical background – What they knew in the early 1900’s Continents and ocean floors –different crusts Features of continents & forces that formed them Continental drift – (1915) Alfred Wegener Reaction to Wegener

Wegener’s lines of evidence that continents drifted 1. Fit of the continents

~4 km thick Pm-J continental deposit s 2. Similar sequence of rocks on all southern continents

3. Similar fossils on all southern continents

Without hair? Lystrosaurus With hair?