Describe the evolutionary history of plant and vertebrates through geological period.
 

About $2000$ million years ago (mya) the first cellular forms of life appeared on earth.

The mechanism of how non-cellular aggregates of giant macromolecules could evolve into cells with membranous envelop is not known.

Some of these cells had the ability to release $\mathrm{O}_{2}$.

The reaction could have been similar to the light reaction in photosynthesis where water is split with the help of solar energy captured and channelised by appropriate light harvesting pigments.

Slowly single - celled organisms became multi-cellular life forms.

By the time of $500$ mya, invertebrates were formed and active.

Jawless fish probably evolved around $350$ mya.

Sea weeds and few plants existed probably around $320$ mya.

We are told that the first organisms that invaded land were plants.

They were widespread on land when animals invaded land.

Fish with stout and strong fins could move on land and go back to water.

This was about $350 \mathrm{mya}$.

In $1938$ , a fish caught in South Africa happened to be a Coelacanth which was thought to be extinct.

These animals called lobefins evolved into the first amphibians that lived on both land and water.

There are no specimens of these left with us.

However, these were ancestors of modern day frogs and salamanders.