How life originated
How life emerged from non-life is an extremely challenging question. As a prelude to the details, let’s review the distinguishing features of living systems in the context of this question.
Origin and Diversity of Life
Life is a continuum extending from the earliest organisms to the great variety of
species that exist today. It is difficult for us to appreciate exactly how far back
life has existed on Earth.
In this unit, we will survey the diversity of life and
trace the evolution of this diversity. Throughout this unit, we will see examples
of the connection between biological history and biological evolution.
If we calculate Earth to be about 4 billion years old and we know that there were
stromatolite–forming bacteria by 3.5 billion years ago, we must assume that living
organisms arose sometime in between.
Where did these living organisms come from?The
conditions on Earth are very different than they were 4 billion years ago. In Earth's
early years the atmosphere was essentially devoid of oxygen and the planet was subjected
to more lightning, UV radiation, and falling meteorites (A stony or metallic mass
of matter that has fallen to the earth's surface from outer space ). Somehow life
managed to arise under these conditions, and various hypotheses attempt to explain
how this might have happened.