Limestone is a sedimentary rock which contains fossils as it is made up of shells and skeletons of tiny sea creatures.

Equator is the imaginary line that passes through the centre of the Earth, dividing it into northern and southern hemispheres.

The process by which wind or flowing water washes away the fertile top part of soil is known as soil erosion.

The Sun is a star around which all the planets revolve. The planets have a fixed path in which they revolve called orbits around the Sun.

In any food chain, primary consumer is an organism that feeds on the primary producers(plants).

Carnivores are predators. They hunt and eat other animals to survive.  

Air is a mixture of gases which contains:
- $78\%$ of nitrogen
- $21\%$ of oxygen
- $1\%$ of other gases
In the given pie chart, 'X' represents nitrogen and 'Y' represents oxygen gas.

Oxygen is consumed in the process of burning. In the process of respiration, oxygen is absorbed and carbon dioxide is released. In the process of photosynthesis, carbon dioxide is absorbed and oxygen is released into atmosphere.