The document discusses geological principles for understanding the Earth's history using the analogy of a layer cake. It explains four key principles: 1) Uniformitarianism - geological processes occurred the same way in the past as today, like how cakes are made the same way each time. 2) Superposition - the oldest sedimentary layers are on the bottom, like how cake layers are placed with the bottom being oldest. 3) Original Horizontality - sedimentary rocks form in horizontal layers, similar to cake layers being placed horizontally. 4) Catastrophism - geological change can occur suddenly, akin to a dropped cake being ruined suddenly.

1. Evocative Question
How are the
geologic
principles for
understandin
g the Earth’s
history like a
layer cake?

2. Uniformitarianism
 The geologic processes that happen today
(mountain building, volcanoes, rocks)
happened the same way in the past AND
change on the Earth is occurring slowly and
constantly.
 How is this like a cake?
 The Principle of Uniformitarianism is like a layer
cake because people basically make cakes the
same way every time.

3. Superposition
 In horizontal sedimentary rock layers, the
oldest layer is at the bottom. Each higher layer
is younger than the layers below it.
 How is this like a layer cake?
 The Principle of Superposition is like a layer cake
because the bottom layer was put down first
(oldest) and the top layer was placed last
(youngest).

4. Original Horizontality
 Sediment settles out of water in
horizontal layers. Larger sediment
settles first and smaller sediment
settles later. Sedimentary rocks form
in horizontal layers.
 How is this like a layer cake?
 The Principle of Original Horizontality is like a
layer cake because the layers should be placed
horizontally.

5. Catastrophism
 Geologic Change occurs suddenly
 How is this like a layer cake?
 The Principle of Catastrophism is like a layer cake
because if you drop it, it’s gone wrong suddenly!
http://www.flickr.com/photos/sylvia/5727154433/sizes/m/in/photostream/http://www.flickr.com/photos/sanfranannie/3639238588/sizes/m/in/photostream/

6. More Simile Examples
 Before you get ready to write your own
similes, here are a few more examples that
are not related to cake.
 The Principle of Superposition is like your dirty
clothes pile. The shirt you wore longest ago is
on the bottom, and the shirt your wore most
recently is on the top.
 The Principle of Uniformitarianism is like riding
a bike. You always ride a bike in the same
way.
 The principle of Original Horizontality is like a
house. The floors in a house are laid out
horizontally.