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Unit 4A Lesson 5 Word Scramble

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Created by: scanto

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Question	Answer
Name two gases common in Earth's atmosphere during the Precambrian time?	Hydrogen and Helium
Scientists used index fossils and rock layers worldwide to determine the:	Geologic Time Scale
What is a body fossil?	A rare fossil in which the entire organism gets preserved.
What is an Index Fossil?	Fossils of organisms that were common worldwide but only lived for a defined period of time in the geologic time scale
On a graph of strontium 90, after two half lives how much radioactive material would remain in a sample?	1/4 or 25%
When did Earth's atmosphere, oceans, and continents began to develop?	During the first several hundred million years of Precambrian time
How are fossils most commonly formed?	When a living thing dies and is quickly covered in sediment
What is a petrified fossil?	Fossils formed when minerals replace all or parts of an organisms body.
What is a mold fossil?	A hollow shape formed when sediment hardens around an organism which later decays
What is a cast fossil?	A solid shape of an organism formed when sediment hardens inside of a hollow mold.
Name 6 types of Fossils that we studied in Unit 4.	Mold, Cast, Index, Petrified, Body , Trace
Carbon 14 and Strontium 90 are two examples of Radioactive elements that scientists use to determine:	The absolute age of a rock or fossil.
What is the absolute age of a rock or fossil	It's actual age in years. (a number- usually in 'mya')
What is the relative age of a rock or fossil?	Its age compared to other rock layers (older/younger)
On a graph of Radioactive decay, at point 0 years, how much radioactive material would remain in a sample?	100% At pt 0, Radioactive decay has JUST begun. Either a living organism has just died OR an igneous rock has just formed.