Certain fossils, called index fossils, help geologists match rock layers. To be useful as an index fossil, a fossil must be widely distributed and represent a type of organism that existed for a brief time period. Index fossils are useful because they tell the relative ages of the rock layers in which they occur.
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There are many ways scientists can gather evidence to learn about Earth's interior including direct evidence from rock samples and indirect evidence from seismic waves.
also
1. Seismic waves and earthquakes
2. Volcanoes
3. Principles of density
4. Earth is magnetic
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Answer:
The Human Immune system helps fight bacteria and germs and viruses because without the Immune system we could die it is what protects us from The flu and sometimes cov id with a weak immune system we might no survive.
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