Origin of life on Earth
How life first came into existence on earth is an interesting question which many people ponder. In order to understand this truly amazing change on the planet I have been reading quite a few articles and books these days.Today via this post I will try to summarise some aspects of early life(which I could understand) on earth in a rather simplified way.Lot of research is going on in this area and hence huge debate about places in the tree of life for various groups.The base of the Tree of Life, and the relationships of the major lineages, are controversial.So its not possible to draw the exact tree of life on earth with the amount of data on hand.
One can find life on every imaginable environment on our planet,from deep into the oceans to high in the sky ,from freezing water of Antarctic to to groundwater thousands of feet below the Earth’s surface.Its now a well accepted fact that Earth is around 4.6 billion years old.There is no direct evidence of earth’s history for the first 700 million years,but rocks have been found that date back 3.8 billion years and first evidence of life dates backs to some 3.5 billion years (micro fossil resembling Cyanobacteria from rocks in Australia).However ,there is a need to take these data on very early life with caution.The more back we go in time the more controversial the claims becomes.During the past 3.5 billion years ,living organisms have diversified and adapted to almost every environment possible.
To trace the rooting of life we take a trip down the memory lane. All animals share common ancestor with Plants and Fungi some 1.2 billion years ago (BYA).It is believed that some special single or multicellular organism gave rise to three major kingdoms of Plants,Fungi and Animals 1.2 BYA.This ancestor of three kingdoms shared ancestor with simple single celled eukarytoes like amoeba ,ciliates and extant (Still in existence) Archaebacteria around 2.2 BYA. As this ancestor was prokaryotic ,all eukaryotic features are assumed to evolved more recently that 2.2 billion years.This prokaryotic ancestor ( of Archea and single celled eukaryotes) share common ancestor with extant Eubacteria around 3.2 BYA.Finally this prokaryotic organism (ancestor of ancestors) is considered to be progenitor of all extant beautiful life forms on Earth.
Terms used in the post :
Archaebacteria: A group of unusual prokaryotic organisms that microscopically resemble true bacteria but differ biochemically and genetically, and form a distinct evolutionary group; some occur widely in oxygen-free environments and produce methane, while others are found in extreme salty or acidic conditions or grow at high temperatures.
Eubacteria :The Eubacteria, also called just “bacteria,” are one of the three main domains of life, along with the Archaea and the Eukaryotes.
Eukaryotes :A single-celled or multicellular organism whose cells contain a distinct membrane-bound nucleus.A eukaryotic cell is a cell with a nucleus and DNA is organised into chromosomes. Plants, animals, protists, and fungi have eukaryotic cells, unlike the Eubacteria and Archaea.Eukaryotes also differ from Prokaryotic cell in having special organelles which perform distinct important functions.
Prokaryotes : An organism of the kingdom Monera comprising the bacteria and cyanobacteria.They are characterized by the absence of a distinct, membrane-bound nucleus and by DNA that is not organized into chromosomes and found freely in cytoplasam.
Note : This tree may not represent exact scenario in the origin of life.This is drawn only for better understanding on the above description(which i believe might have happened billions of years ago) about evolution of early life.
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