Common Core: 7th Grade English Language Arts : Analyze How Individuals, Events, and Topics Interact in a Text: CCSS.ELA-LITERACY.RI.7.3
Study concepts, example questions & explanations for Common Core: 7th Grade English Language Arts
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Example Questions
Example Question #3 : Reading: Informational Text
“Stone Trees”
Have you ever seen a stone tree? While the idea of a stone tree may sound fantastic, fallen trees can turn to stone in very specific circumstances, producing what scientists call “petrified wood.” “Petra” means stone in ancient Greek, so something “petrified” has been turned to stone. You may have heard the word “petrified” used to describe someone so scared that they have frozen as if turned to stone, but scientists use the word literally to refer to actual stone. Petrified trees are stone trees, not scared trees!
A Type of Fossil
Like ancient skeletons of dinosaurs and other organisms preserved in the earth, petrified wood is a type of fossil; however, there is a big difference between petrified wood and most fossils. Most fossils are imprints of creatures or partial remains of them, such as their skeletons. In contrast, the process of petrification recreates an entire preserved tree in stone. It’s very cool to see a petrified tree close-up, because it is still precisely life-size; you can get an idea of how big the tree was when it was alive, and even see individual tree cells that have been preserved. You can even count the tree rings in some petrified trees and estimate how old the tree grew to be before it was petrified.
From Tree to Stone
In order for a tree to become petrified wood, it must have died and been buried a very long time ago. This has to have happened in a specific environment, though, or petrified wood would not be so rare. The tree has to be buried in such a way that oxygen cannot get to its bark and wood. If oxygen can get to the tree, it will rot instead of turn to stone.
The environment has to have two more specific characteristics to produce petrified wood: there has to be water in the ground around the tree, and that water has to contain minerals. If mineral-containing water is present, water will go into and out of the tree’s cells and, over time, the minerals in the water will accumulate in the tree’s cells. When the tree’s cells eventually decay, the minerals are left. Petrified wood can be a rainbow of different colors, with each color corresponding to different elements in the tree’s preserving environment that affect the color of the minerals that form its stone.
Petrified wood is found all over the world, and there are even entire forests of petrified trees that you can travel to go see today. One national park in the United States, Petrified Forest National Park in Arizona, is famous for its many petrified trees. The next time you see a tree, remember, after a few million years in the right environment, it could turn to stone!
In what way does petrified wood differ from dinosaur fossils?
Dinosaur fossils are much more valuable than petrified wood is.
Dinosaur fossils can only form when oxygen does not get to the organism being fossilized, but petrification requires that a tree be exposed to oxygen.
Dinosaur fossils are always bigger than petrified trees.
Dinosaur fossils are parts of ancient creatures, but petrification preserves the likeness of an entire tree.
Dinosaur fossils are two-dimensional imprints, but petrification creates a three-dimensional stone tree.
Dinosaur fossils are parts of ancient creatures, but petrification preserves the likeness of an entire tree.
In the section "A Type of Fossil," the passage compares petrified wood to other fossils like dinosaur bones and imprints. The section begins by setting up for discussion of "a big difference" between petrified wood and most other fossils:
Like ancient skeletons of dinosaurs and other organisms preserved in the earth, petrified wood is a type of fossil; however, there is a big difference between petrified wood and most fossils. Most fossils are imprints of creatures or partial remains of them, such as their skeletons. In contrast, the process of petrification recreates an entire preserved tree in stone.
This answers the question at hand: dinosaur fossils are parts of ancient creatures, but petrification preserves the likeness of an entire tree. This is the correct answer. The passage doesn't say anything about dinosaur fossils always being bigger than petrified trees, nor does it say anything about the relative value of dinosaur fossils and petrified wood. The answer choice "Dinosaur fossils can only form when oxygen does not get to the organism being fossilized, but petrification requires that a tree be exposed to oxygen" may seem correct, but read it carefully, and you'll find that its last part, "petrification requires that a tree be exposed to oxygen," is incorrect based on what we learn in the rest of the passage. Petrified trees only form when fallen trees are prevented from rotting by being buried so oxygen can't get to them and make them rot. "Dinosaur fossils are two-dimensional imprints, but petrification creates a three-dimensional stone tree" may also look like a great answer choice; however, the passage states, "Most fossils are imprints of creatures or partial remains of them, such as their skeletons." Skeletons aren't two-dimensional imprints, so we can't claim that "Dinosaur fossils are two-dimensional imprints."
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All Common Core: 7th Grade English Language Arts Resources
