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Cyanobac­te­ria were the first liv­ing organisms

Since the first life appeared in the Earth’s oceans about 3.8-billion years ago, the pat­tern of life on our plan­et has become increas­ing­ly complex.

Life has devel­oped from those sim­ple organ­isms, explod­ing into more than 1.3-million doc­u­ment­ed species of liv­ing things on Earth today. Sci­en­tists esti­mate there are between 30-mil­lion and 100 – mil­lion species on Earth, though only about 1.3 – mil­lion of these have been documented.

The devel­op­ment of life on Earth as we know it has gen­er­al­ly been grad­ual, although there have been peri­ods of rapid change. The most pro­lif­ic pro­fu­sion of species has occurred dur­ing the last eighth of Earth’s his­to­ry, known as the Phanero­zoic Era, with­in the past 543-mil­lion years.

Among the Earth’s first organ­isms were cyanobac­te­ria: tiny, sin­gle-celled crea­tures which formed a film over the sur­face of mud and trapped coats of it, mak­ing lay­ered struc­tures called stro­ma­to­lites. Stro­ma­to­lites emerged soon after the Earth cooled and the atmos­phere and oceans formed. Although now near­ly extinct, these micro­bial mats are still form­ing in some places, such as in the high­ly saline waters of Shark Bay, in West­ern Australia.

Fos­sil stro­ma­to­lites have been dis­cov­ered in a wide vari­ety of envi­ron­ments, from ther­mal springs to lakes, the sea and even below ice-cov­ered lakes in Antarc­ti­ca. Sci­en­tists have found fos­sil traces of stro­ma­to­lites which are about 3.5-billion years old – some of the world’s old­est – near Bar­ber­ton in the Mpumalan­ga Province of South Africa. Stro­ma­to­lite fos­sils of a sim­i­lar age have also been found in north-west­ern Aus­tralia and Green­land. Fos­sil stro­ma­to­lites have also been found at Sterkfontein.

The stro­ma­to­lite fos­sil record is almost the only evi­dence we have of life on Earth for the first s

even-eighths of the planet’s existence.


The last eighth of the Earth’s his­to­ry saw an explo­sion of life. 

About 600-mil­lion years ago, the first sponges, jel­ly­fish and flat worms appeared in the oceans. The first arthro­pods – mil­li­pedes and cen­tipedes, and lat­er spi­ders and scor­pi­ons – moved onto land about 450-mil­lion years ago. Insects first evolved about 400-mil­lion years ago and rep­tiles about 330-mil­lion years ago. The first mam­mals appeared about 220-mil­lion years ago, and the first birds about 150-mil­lion years ago. The first flow­er­ing plants began to grow about 118-mil­lion years ago. The last dinosaurs were wiped out about 65-mil­lion years ago, and the first pri­mates – our ancient ances­tors – appeared about 55-mil­lion years ago.

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Earth is home to more than 4000 species of mammal

At present, clas­si­fied species include 4,000 dif­fer­ent mam­mals, 9,000 birds and 750,000 types of insects.

But hun­dreds – pos­si­bly thou­sands – of species are becom­ing extinct every year. Some esti­mates put the num­ber of species dying out at about 100 every day; even con­ser­v­a­tive records of extinc­tions run to more than 500 a year.

Sci­en­tists regard Africa as a rem­nant of the Earth’s past diver­si­ty. Its rel­a­tive­ly sparse human pop­u­la­tions until now have allowed peo­ple and a great range of oth­er species to co-exist. But this is chang­ing fast. The amaz­ing bio­di­ver­si­ty of life on Earth is now under seri­ous threat.

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