All terms in this list:
Density: Mass of a unit volume of a substance. Density = M/V kg per cubic m or g per cubic cm
Life of Earth depends on what? And why?: The Sun. Because most form of energy that we use comes directly or indirectly from the sun.
When and How were fossil fuels formed?: Millions of years ago. From prehistoric forest and marine animals due to lack of air, intense pressure and heat. Coal - forest Oil - marine animals
Renewable energy sources: They use processes that are part of our natural environment to supply energy. They are constantly being replanished.
Non-renewable energy sources: One supplies have been used they cannot be replaced.
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