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The famous Lit­tle Foot fossil.

Fos­sils are the remains of plants and ani­mals that have been pre­served in sed­i­men­ta­ry rocks. Fos­sils are gen­er­al­ly rare. For every ani­mal that dies, its chances of becom­ing fos­silised are esti­mat­ed to be less than one in a mil­lion. But at the Cra­dle of Humankind, the chances are greater because the area has the right mix of con­di­tions that pro­mote fossilisation.

How are fos­sils formed?

For a fos­sil to be suc­cess­ful­ly formed and found, a num­ber of steps have to take place in suc­ces­sion. One missed step, and the ancient remains of an ani­mal or plant will either not be pre­served, or not be discovered.

Fos­sils are formed when min­er­als such as cal­ci­um car­bon­ate enve­lope or replace bones and oth­er organ­ic mat­ter, hard­en­ing or cast­ing them with­in a rock matrix such as brec­cia that remains unchanged for mil­lions of years.

If the sed­i­ment is com­posed of the right min­er­als, it can suf­fuse through the bones and organ­ic mate­r­i­al, mak­ing them as hard as rock in a process called min­er­al­i­sa­tion”. Over mil­lions of years, these fos­sils are cov­ered by lay­ers of new rock and sediments.

Final­ly, either through nat­ur­al occur­rences like ero­sion, earth­quakes or human activ­i­ty, such as lime­stone min­ing, the fos­sils can become exposed again, giv­ing sci­en­tists a win­dow to our past.

Evi­dence from the study of fossils

Palaeon­tol­o­gists exam­ine the age, char­ac­ter­is­tics and sur­round­ing envi­ron­ment of a fos­silised ani­mal to under­stand its place on the evo­lu­tion­ary timeline.

The age of fos­sils can be deter­mined using radio-iso­tope dat­ing on rocks close to them. Some chem­i­cal ele­ments occur in slight­ly dif­fer­ent forms called iso­topes, and some of these iso­topes found in rocks are unsta­ble and decay over mil­lions of years at a set rate.

By check­ing the amount of decay of an iso­tope, sci­en­tists can work back­wards and deter­mine how old a rock is – and from that esti­mate the age of a fossil.

Once a few species have been clas­si­fied, experts can start to exam­ine trends in the evo­lu­tion of animals.

For instance, with fos­silised remains of Aus­tralo­p­ithe­cus africanus and Homo ergaster in the Sterk­fontein deposits, we can see the trend towards a big­ger brain as hominids evolved.

The Cra­dle of Humankind gives us some of the rich­est evi­dence of our ear­li­est direct ances­tors – Aus­tralo­p­ithe­cus africanus and Homo ergaster hominids – and our dis­tant cousins”, Paran­thro­pus robus­tus.

Fos­sils from some of the ear­li­est organ­isms ever dis­cov­ered have been found in South Africa and date to about 3.5-billion years ago.

Palaeon­tol­o­gists have also found remains of our dis­tant mam­malian ances­tors that lived more than 200-mil­lion years ago and fos­sils of some of the ear­li­est known dinosaurs from about the same peri­od, in the Karoo.

Return to the Exhi­bi­tion Guide.