The organisms with hard parts are likely to be fossilised, than those who do not have such parts. The harder the material, better it would be preserved soft parts fossils occur rarely, e.g., birds and pterosaurs have very light bones, hollowed out and specialised for flight.

So, they have sparser fossil record as compared to mammals, whose bones are partially mineralised during life.

Yes, aquatic forms of life do get fossilised, infact, there are more aquatic than terrestrial fossil organisms. Such fossils of sea creatures are found in mountains as opposed to deep sea beds.

This is because the rocks in which the fossils are found used to be at the bottom of oceans. Due to the changes in the crustal plates over time, the ocean sediments were pushed up to form mountains.

These terms are used to classify organisms according to their evolutionary history.

Simple organisms refer to those organisms that have simple structural and functional organisation and are considered primitive, whereas Complex organisms refer to those organisms that have higher and complex levels of structural and functional organisation.

These are more advanced and said to have arisen from simple organisms.

To estimate the age of a living tree, following steps are required

(i) Measure the circumference of the tree trunk (at about 4.5 feet above the ground).

(ii) Calculate the diameter of the trunk. This is done by dividing the circumference by 3.14. Divide this (i.e., diameter) by 2 to get the radius.

(iii) Determine the growth factor. A tree's growth factor is the measurement of the width it gains annually. The trees's growth factor can be seen from the data available or by measuring the rings of a dead tree from the same species.

(iv) Multiply the diameter and the tree species average growth factor and the so done calculating suggest the approximate age of the tree in years.