Across
- 3. amount of time it takes for a radio active isotope to decay 1/2
- 6. type of element that has the same atomic number but different atomic mass
- 7. structures or organs in the body that serve no purpose but were useful to earlier ancestors
- 8. body structures that are same general shape but used for different functions
- 10. a fertilized egg that is growing into a new organism
Down
- 1. body structures that are used for the same function but not the same shape
- 2. first type of cells
- 4. largest time classification
- 5. the Earth is 4.6...years old
- 9. this vital element didn't show up until 1.8 billion years ago