Early signs of Life (Important Facts) {Part-12}

FOR ALMOST A THOUSAND MILLION YEARS after its formation, there was no known life on Earth. The first simple, sea-dwelling organic structures appeared about 3,500 million years ago; they may have formed when certain chemical molecules joined together.

Stromatolitic Limestone

Prokaryotes, single-celled micro-organisms such as blue-green algae, were able to photosynthesize , and thus produce oxygen had built up in the earth's atmosphere to allow multicellular organisms to proliferate in the Precambrian seas (before 570 million years ago).

Fossilized Jawless Fish

Soft-bodied jellyfish, corals and seaworms flourished about 700 million years ago. Trilobites, the first animals with hard body frames, developed during the Cambrian period (570-519 million years ago).

Fossilized Trilobite

However, it was not until the beginning of the Devonian period (409-363 million years ago) that early land plants, such as Asteroxylon, formed a water-retaining cuticle, which ended their dependence on an amphibians crawled onto the land, although they probably still returned to the water to lay their soft eggs.
By the time the first reptiles and synapsids appeared late in the Carboniferous, animals with backbones ad become fully independent of water.