FMBR Editorial: April, 2002
Emergence of Life
William C. Gough
Science tells a fascinating story about the emergence of life on Earth and its evolution into ever more complex forms. To put this process into perspective let's condense the four billion years of the Earth's existence into one year. On such a scale the universe started less than three years earlier. On January 1st the earth has areas ravaged by volcanoes and earthquakes, there is no oxygen, and radiation from the solar winds is bombarding the planet. Slowly water appears from the ice in asteroids, comets and magma and creates the primordial seas. The most ancient creatures to appear are prokaryotic cells that have no nucleus. By February 14th molecules that constantly assemble and disassemble themselves appear. A major advance in the history of life has happened -- replication. The ingenious biological invention of photosynthesis occurs permitting the release of oxygen, making life as we know it today possible. By July 1st the air has cooled and volcanic eruptions have diminished. Two billion years have passed and all life is still based upon the same underlying design -- a cell without a nucleus.
It is now August 24th and the prokaryotic cell is still dominant (1.4 billion years ago) but the environment is being poisoned by oxygen which can destroy the primitive cells in the oceans. Then an extraordinary biochemical "invention" occurs, the aerobic cell -- the first living creature to use oxygen for its vital processes, i.e., to "breathe". By October the amoeba appears. The photosynthesis of microorganisms is producing so much oxygen that it is escaping from the ocean and spreading into the atmosphere. From November on the ozone layer in the Earth's upper atmosphere will allow life to start to emerge and conquer dry land. For billions of years now all life has had to remain under water to protect itself from the ultraviolet radiation of the sun -- the land is barren: there is no grass, no vegetation, no life.
From September 28th to October 16th, 1 billion to 800 million years ago, cooperation becomes a major force. Atoms assemble to create molecules and these in turn create other basic structures of life like DNA and proteins. The outcome is colonies of highly organized and specialized cells that cooperate -- the forerunners of plants, animals, and us. By November 5th we have jellyfish. Neural ganglia, tangles of nerve cells, that are the first steps towards a brain appear. By November 8th to 15th, a relatively short time span, an incredible range of diverse animal life appear. On November 22nd the first landing troops arrive on dry land -- they are forms of plant life like moss. By the end of November invertebrates like the millipedes and scorpions had landed. In the seas there is a decisive anatomic invention: the jaw -- sharks appear. Then the vertebrates arrive on land -- the ancestors of todays animals like snakes, horses, etc.
By December 3rd, 310 million years ago, there are immense forests with trees as tall as a ten-story building which eventually became our coal deposits. However, on December 8th an ecological catastrophe occurs and again it is the climate that conditions and selects the life that is to evolve on Earth. The glaciers melt and the temperature at the poles are 50-60 F. Dinosaurs, a type of reptile, dominate -- in fact reptiles will control the land, water, and air environments for the next 200 million years. Only very small mammals manage to survive. By December 23rd and 24th color appears on land with the advent of flowers, and birds, the closest relative of the dinosaurs, fill the sky -- including the ancestors of seagulls.
Although there have been at least twelve other climatic extinctions known to have taken place, the one that occurs on December 25th (65 million years ago) is the most impressive. This catastrophe, a change in climate with a sudden cooling, eliminates the Earth's dominate species. The earth is like a theater that has been emptied. With the disappearance of the dinosaurs, new environmental niches for small mammals open up and they grow in size and number.
Finally, on the last day of the year, December 31st (2 million years ago), one of these mammals, Homo habilis or man, appears in Africa. But it isn't until ten minutes before midnight on New Years Eve that our immediate ancestors, Homo sapiens, make their appearance. One of their keys to success is the increase in brain volume from 600 cc for Homo habilis to about 1300 cc in modern human beings.
The number of neurons increases to ten billion, and hence the capability for processing information magnifies enormously. Yet other species also developed extraordinary brains like the dolphin and became highly intelligent. However, in man there occurs a radical re-engineering of the whole brain, an evolution in which language is reflected in the very architecture of the brain. Man develops a unique ability to express symbols and quickly becomes the dominate species.
We are in Times Square, New York City for the New Years Eve celebration. Shortly before the big ball is dropped and the count down begins, writing is developed and the first Egyptian monuments appear. With one minute to go the first steam engines operate and the Industrial Revolution begins. The ball starts falling. With five seconds to go World War I begins, with two seconds to go Homo sapiens set foot on the moon. As the ball hits the ground and a new year starts, we find that our species is seriously affecting the Earth's environment including depleting the protective ozone layer -- and we are now capable of genetically engineering the creation of new species. What will be our future? The history of life on our planet says that environmental changes are the key factor for the demise of species. In fact 99.99% of all species that ever existed on Earth are now extinct. However, there has been one constant -- life always continues!
William C. Gough, Apr 2002
Piero and Alberto Angela, The Extraordinary Story of Life on Earth, Amherst NY: Prometheus Books, 1996
Terrence W. Deacon, The Symbolic Species: The Co-evolution of Language and the Brain, NY: W.W. Norton & Co., 1997