It's hard to fully
comprehend the
depth of time past. The universe came into existence some 13.8
billion years ago (BYA). The earth was formed around 4.5 BYA. The
first signs of life – simple microbes – appear about 3.5 BYA.
But as presented in a wonderful book about just how complex and
essential they are – Life's
Engines: How Microbes Made Earth Habitable by Paul Falkowski
– microbes are anything but simple. Microbes – bacteria and
archaea – are prokaryotes, single cell life without a nucleus or
organelles. Everything else – single cell or multi-cell plants and
animals – are eukaryotes: cells containing a nucleus and
organelles such as mitochondria. The prokaryotes developed the
ability to extract energy from the chemical environment and,
eventually, from the sun. It took another two billion years for them
to evolve into complex cells: the eukaryotes.
Two billion years is
a long time. Why did it take that long to go from bacteria and
archaea to the first eukaryotes? The machinery to convert chemicals
such as hydrogen sulfide or ammonia, and then the much harder task of
using sunlight, to fuel life would have taken a long time to develop.
But not just that. Extracting energy from the environment meant a
complex process of freeing electrons from chemical bonds,
transferring those electrons around within the cell and using them
ultimately to create other chemicals that would store those electrons
(i.e., serve as “food”) to provide energy for cellular processes.
Photosynthesis is an even more complex process that uses sunlight to
crack electrons from water and combine them – through intermediate
steps – with carbon dioxide to produce carbohydrates and, as a
waste product, oxygen. This complex machinery had to evolve step by
step through the repeated random changes in DNA and RNA as winnowed
through natural selection. (A good part of the first billion years
after the formation of earth would have been used for the
construction of the RNA/DNA mechanism itself.) As Falkowski argues,
the processes for producing and consuming biologic energy work as
tightly as a complex and precise system of interlocking gears: one
out of place and the whole won't work. All the parts of the
machinery had to come on line more or less at once or it would not
function. Somehow, the machinery evolved anyway, implying that a lot
of time was required for vastly more failures – in which the
resulting organism from random mutation simply died – than
successes.
That the machinery
was there to be evolved – that the givens of the universe
allowed such a thing to come into existence – is also
worth pondering. As is the fact that we would not be here
otherwise.