20. The answer is 1 (Precambrian)
21. The answer is 4 (Pennsylvanian)
22. The answer is 2 (Bony Fishes, Dinosaurs, and Mammals)
23. The answer is 2 (Reptiles)
Answer:
The amount of energy in the first level determines how many animals can be supported on the subsequent levels.
The first level of the energy pyramid usually consists of the producers which are the main source of energy for a food web or a food chain. They determine that how many number of species can be supported by the particular ecosystems at each subsequent levels of the energy pyramid. They are the main source through which energy arises in an ecosystem.
DNA molecule was instrumental in the formulation of the modern cell theory.
Answer:
Mass extinctions happen because of climate change, asteroid impacts, massive volcanic eruptions or a combination of these causes. One famous mass extinction event is the one that lead to the extinction of dinosaurs, 65 million years ago.
Explanation:
