Unit 4A Exam Review Word Scramble
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| Question | Answer |
| What has the study of fossils allowed scientists to do? | Describe past environments and the history of life |
| What are ideal conditions to fossilize remains of an ENTIRE organism? | Very rapid burial or freezing |
| True or False? Footprints and trails are examples of trace fossils. | True |
| How is a petrified fossil formed? | When minerals replace parts of an organism |
| What is the relative age of a rock? | It's age compared to the rock layers that surround it |
| What is the absolute age of a rock | It's age in years |
| How is the absolute age of a rock determined? | By radioactive dating |
| What is a 'half-life' of a radioactive element? | The number of years it takes for half of the radioactive element to decay. |
| On a graph of radioactive decay, how can you determine the element's half life? | The half-life is the point on the graph (in years) in which 50% of the radioactive content has decayed |
| When determining the relative age of rocks, the concept that 'the deeper the rock layer, the older the rock' is known as: | The Law of Superposition. |
| What two things must occur to create an 'unconformity' in rock layers? | First, a rock layer is eroded. Second, a new sediment layer is deposited. |
| The breakdown of an unstable element to form atoms of another element is known as: | Radioactive decay. |
| When did marine invertebrates first appear in the fossil record? | During the Cambrian explosion of the Paleozoic era |
| When did marine vertebrates first appear in the fossil record? | During the Ordovician period of the Paleozoic era |
| When did amphibians first appear in the fossil record? | During the Devonian period of the Paleozoic era |
| Which era is commonly known as 'the age of reptiles' when dinosaurs were common on land? | The Mesozoic era |
| Which era is commonly called 'the age of mammals' when mammals were common on land? | The Cenozoic era |
| Why is the Quaternary period of the Cenozoic era significant? | Humans appear in the fossil record. |
| The record of geologic events and the history of the evolution of life forms as shown in the fossil record is commonly called the: | Geologic Time Scale |
| In a diagram of rock layers, how could you determine which rock layer is the oldest? | According to the law of superposition, the deeper the rock layer, the older it is. |
| In relative aging of rocks, if a boundary between rock layers has been eroded away and a new sediment layer has been deposited on top, what is that called? | An unconformity |
| How is the Geologic Time Scale organized? | It is divided into Eons, eras, periods, and epochs. |
| How/why do geologists use the Geologic Time Scale? | Scientist's use the Time Scale to record and keep track of Earth's history. |
| If the half life of a 20g sample is known to be 24 minutes, How long will it take for only 10g of the sample to remain? | 24 minutes |
| True or False? Geologists divide Earth's long history into smaller units that make up the Geologic Time Scale? | True, Geologists have divided Earth's long history into eons, eras, periods, and epochs. |
| What information in the fossil record helps Geologists determine the boundaries between time periods in the Geologic Time Scale? | The appearance or disappearance of species commonly found in the fossil record. |
| How did Geologists develop the Geological Time Scale? | By studying rock layers and index fossils worldwide. |
| What is an index fossil? | A fossil used by geologists for indexing and defining geologic periods |
| True or False? Earth's atmosphere, oceans, and continents began to form during the first several hundred million years of Precambrian time. | True. |
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