Biology 105 Origin and Diversity of Life
I. Origin of Life
A. Science provides evidence to explain the origin of life, using ideas of evolution and knowledge of chemistry
B. To understand how life could have evolved, we need to know what the very early Earth was like.
1. The Earth was formed about 4.5 bya (billion years ago), and conditions then were very different than they
a. The atmosphere was thought to include hydrogen gas, ammonia, methane, carbon dioxide, carbon
monoxide, and water vapor, but no oxygen.
b. There were severe storms with lightning, strong UV light, and constant volcanic eruptions supplying
energy to these atmospheric chemicals.
c. A Russian scientist, Oparin, hypothesized that these atmospheric gasses, when given energy, would react
to form organic (cellular) molecules.
d. This hypothesis was tested by an American scientist, Miller. He put the gasses into an apparatus with
circulating water and used sparks to simulate lightning. In only a few weeks he succeeded in making many organic
molecules, similar to those found in cells, in his 'primitive Earth' apparatus.
C. Scientists now believe that similar cellular molecules were in fact formed on the primitive Earth and slowly
built up in the oceans, forming a mixture called the “primordial soup”. Somehow primitive cells evolved in the
primordial soup and lived by eating these molecules.
1. Nobody knows quite how this happened, but natural selection clearly would have played a big role. Cells or
even proto-cells that were good at getting what they needed would persist and reproduce, while others would fall
apart or be eaten.
a. The requirements needed to make a cell out of non-living materials seem to be:
i. a boundary, or membrane, between the cell and its environment
ii. controlled chemical activity, or some sort of metabolism, in the cell, and
iii. a way to store and use the biological information needed to produce the metabolic enzymes and
membrane (there is evidence that this was RNA in the first cells)
b. Once a cell had achieved all of these, it could be considered alive. However, evolution could occur even
in the pre-living state, and maybe helped cells become alive.
2. The first primitive cells formed in this way were anaerobic (non oxygen-using), procaryotic cells -- small
primitive cells lacking a nucleus or other internal parts, like bacteria today.
D. After these first prokaryotic cells evolved, the Earth's first ecological crisis occurred. Cells were consuming
the organic molecules much faster than they could be made. Even if the cells could eat each other, they were still
limited by the original small supply of abiotically-formed organic molecules. The future of life on Earth appeared