Rock Cycle 9/12/18

Rock Cycle by L.E.

The Rock Cycle

Geology is the study of the structure of the planet Earth and the forces that make and shape this planet. Geology literally means “study of the Earth”. “Geo” means “Earth” and “logos” means “study of”. 

If things like volcanoes and earthquakes shape mountains and monuments in the present day, we can estimate what could have happened in the past. Rocks that are around today could have been around in the past.

Geologists classify rocks into three main groups: igneous, sedimentary, and metamorphic. 

Igneous rocks are made of fire. They form when molten material from the Earth’s core hardens and cools inside or outside of the Earth’s crust. Igneous rocks can look entirely different from each other based on their rate of cooling or where they cooled. If an igneous rock hardened closer to the Earth’s core than one that hardened on or closer to the surface.

Sedimentary rocks are made through settling. They are made from sediments that have been deposited and then forced together to create a rock. Sedimentary rocks can have sand, dirt, fossils, and shells in them because all of these things are carried through sediments.

Metamorphic rocks are made through change. They are formed when a rock that ALREADY EXISTS is changed by immense amounts of intense heat and pressure or a chemical reaction. 

The rock cycle is a series of processes on and beneath the Earth’s surface that transforms one type of rock to another and back again over time. The rock cycle is the Earth’s way of changing rocks.

Relative and Absolute Age:

The Geologic Time Scale is a record of Earth’s life forms and geologic events in Earth’s history. 

We do not talk calendars when we talk about the Earth’s geologic history because Earth is 4.6 billion years old and calendars are 2,018 years old. 

Geologists use both relative and absolute age depending on what organism it is. 

Relative age is the age of a rock or fossil compared to the rocks or fossils near or around it. Absolute age is the age of a rock since it was first formed. Everyone and everything has a relative and absolute age. 

The law of superposition states that in a horizontal sedimentary rock layer, the oldest layer is at the bottom. The youngest, or most recent, is at the top. The law of superposition helps us determine the relative age in a sedimentary rock layer. 

Determining Relative age:

Cross-cutting principle: when something cuts across a body of rock, the ‘something’ is ALWAYS younger than the rock it cuts across. 

Clues from igneous rock:

Magma that hardens on the surface of the Earth is called an extrusion. An extrusion is always younger than the rocks/soil around or near them. Magma that cools and hardens below the Earth’s surface is called an intrusion. Intrusions are always younger than the soil around them. This is because the rocks and soil were there before the magma cooled and made the igneous rocks. 

Clues from faults:

Faults are always younger than the rocks/plates they cut across. 

Imagine a hole. The hole is younger than the area of soil, grass and rocks around it. You can’t have a hole first and then the rocks, grass and soil. The hole or fault is always going to be younger. 

Index fossils help geologists match rock layers and help to determine the relative ages of rocks in which they occur. To be useful as an index fossil, a fossil must be widely distributed and represent a type of organism that existed/lived only briefly. 

S&EP: SP2

I used models to visually explain how geologists use fossils to estimate relative and absolute age. We used a fossil simulation to match the layers of fossils and help us determine which creatures existed when. We also used a Task simulation on goformative that helped us order the fossils from the oldest on the bottom to the most recent on the top. 

Models are useful in situations like these because they can help you grasp better understanding of the tasks at hand and can help you learn things, like how to estimate relative and absolute age, how to order fossils based on age, and how to make inferences based on your discoveries. 

XCC: Patterns

This image displays an example of a pattern we’ve used in class. This is a screenshot of the fossil simulation that we used to help us. The oldest layer of fossils is on the bottom. 

You are able to see where the same types of organisms line up with each other. This is a pattern, because an organism cannot go extinct and then randomly appear again. Some may live for longer than others, like the fossils that line up in every segment, but some might only live for a little while, like the fossils that accumulate in only one or two of the segments. 

Some organisms can live before others do and live long after some go extinct. Some organisms are able to survive longer than others, or other animals might’ve preyed on the smaller ones, causing them to go extinct before the more carnivorous ones.