It is extremely rare for any nutrients to escape the recycling of matter in food webs.

When large organisms die, they are normally dispersed or eaten by scavengers. 

Soft-bodied organisms cannot be fossilised, so they leave no trace. 

Plant remains, such as fallen trees, are decomposed by fungi and bacteria. 

Usually only a few hard parts remain, such as exoskeletons and teeth.

Carbon-14: half-life of 5700 years

Uranium-235: half-life of 704 million years

Relative dating: the process of determining the order of past events.

Relative dating cannot determine the age of fossils and rocks; it can only determine whether they are older, younger or the same age as fossils and rocks found near them.

There is evidence of five mass extinctions since life began on Earth. A variety of pressures, including human actions, can lead to species extinction.

Homology:a structural or developmental similarity based on descent from common ancestors. Example: mammals and amphibians have four limbs.

Homologous Structures: body parts that are similar because the species have evolved from a common ancestors. 

Is used to compare structural and developmental patterns at molecular levels. Example: nucleotides, amino acid sequences and protein structure between extant and extinct species.

Variation exists in populations

More offspring are produced than can possibly survive to reproduce in a population.

In the struggle for survival, those organisms better suited to their environment survive in greater numbers than those less suited. 

Surviving organisms breed and pass on the genes that helped them survive to the next generation.

Over time, the population is dominated by those organisms with the genes best suited to surviving in the current environment.

There needs to be:

Variation within a species

Isolation and competition

Selection and speciation

Reproduce via the fusion of two genetically different gametes.

Variation within meiosis:

Mutations during interphase (DNA replication)

Crossing-over during prophase I

Homologous chromosomes are aligned and randomly selected during anaphase I.

Offspring have a unique set of DNA

Reproduce via mitosis 

Produces identical offspring. 

u

Can lead to speciation.


Competition

uDifferent species who share a local area are in competition for resources. 

The ecosystem may not be sufficient to support all species.

uLimited resources poses selection pressures on those competing species and can help lead to speciation. 

uSelection pressures: the driving force that organisms with a particular favourscharacteristic over those without. 

The species with the most advantageous trait will survive over other species with less favourabletraits.


Speciation
Formation of separate species (that were once the same) due to selection pressures. 

Examples: competition and isolation

uBacteria can develop a resistance to antibiotics leading to “superbugs”

Native Australian marsupials have evolved and adapted to our native Australian plants. Due to evolution and natural selection our native marsupials have grown up eating gastrolobium plants, these plants contain the same compound as the poison used to control the introduced species population (poison 1080).

Artificial Selection: intentional breeding for certain characteristics