FOSSILS AND EVIDENCES OF EVOLUTION

Fossil
- any preserved part or trace of an organism that once lived.
- it is formed when substance in the soil replace the soft, easily decomposed part of a dead organism.
- Other organisms like mosquitoes and spiders are sometimes covered with resin. The resin hardens, forming amber.

Fossil Reconstruction
- Scientists gather pieces of fossils, reconstruct them to form a complete structure, and compare them with structures of living organisms.
- Scientists work with other artists who compare the shape of the skeleton to determine an ancients organism's posture ans style of walking.
- Some may even determine the shape of the preserved organism by detecting muscle attachments and using clay molds.

Types of Fossils
1. Imprints - are formed when soft body structures such as feathers and leaves form impressions on sedimentary rocks.

2. Molds - are depressions on the rock and are shaped like the part of the organism such as teeth, shells, and bones.

3. Cast - it is formed when a mold is filled with another material.

4. Petrified Fossils - are formed when minerals replace the hard parts of organisms.

Fossils can be formed in 3 processes:

1. Replacement - is the process through which the original mineral is replaced by other minerals that seep in from the environment.

2. Molds and Casts

3. Recrystallization - only outline of the original material is preserved.

Evidences of Evolution

1. Embryonic Development
- organisms in their early stages of development are called embryo.
- embryonic development among species reveal similarities with their "ancestors".
- during development process embryos look alike because organisms may have the same ancestral roots.

2. Homologous and Analogous Structures

Homologous structures - some organisms of different groups have body parts that are similar in structure but have different functions.
Analogous structure - are those that have similar functions but different anatomical structures. Example butterfly's wings have the same function as the bat's wings.
3. Vestigial Structures - are parts of the body with no particular function. The existence of these structures indicates that the changes have taken place through time and that the ancestral roots of the organisms with these structures may be the same.

4. Biochemical Evidences - indicates that living organisms share a common ancestor. Variation is formed in the protein structure of one group of organisms as they evolve into another group.The greater are the similarities in the protein structures, the closer is the relationship between the organisms.