Investigating human origins with fossils

The investigation in human origins is kind of like a detective story.  Clues lead the anthropologist on a search for evidence, using techniques developed in many other fields of science, such as geology, chemistry and zoology, this is why this topic is of real interest to me as well as the many others.  I have started to collect mineral and rocks but do not have any fossils, to purchase them they cost a lot of money. Not only are they valuable to collectors, but are essential in the investigation into human origins.  The search for evidence still continues today at an increasing rate.  As new techniques are developed, new knowledge is built on and foundations laid in the past.

Any preserved trace left by a previously living organism is, of course, a fossil.  Bones and teeth are the most common to be fossilised, but preserved footprints, faces and other remains can provide some really valuable information.

When we consider billions of organisms that have lived on earth, the chance that the individual plant or animal will be fossilised is very small.  Normally, dead organisms are decayed by micro-organisms and no trace of their existence is left.  Parts of organisms may become fossilised when they are buried by drifting sand, mud deposits by rivers, volcanic ash, or, in the case with more recent human ancestors, by other members of the species.  If buried rapidly, conditions may not be suitable for the activity of decay organisms and decomposition may be slowed or prevented.

The nature of the soil is very important for the fossilisation of bone.  In wet, acid soils minerals in the bones are dissolved and no fossilisation occurs.   However if the wet, acid soil contains no oxygen, like peat for example, complete preservation of the soft tissues of animals as well as bones may occur.  
Bones buried with alkali soils produce the best fossils since the minerals in the bones are not dissolved. New minerals, often lime or iron oxide, are deposited in the pore of the bones, replacing organic matter that makes up about 35% I think by weight of the bone.  The bone turns into rock, it becomes 'petrified' (seen Harry Potter?) but the details and structure are still preserved.

Fossil ancestors are often found at the edges of ancient lakes and river systems, in caves or in volcanically active areas.  It is unusual for animals to be preserved near volcanic eruptions because the heat would obviously destroy the organism, but in East Africa, ash falls have preserved fossils of many human ancestors.  Most fossils are found by chance, but also by painstaking excavation of likely sites.