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For a sampling of articles that have appeared in Naturalist Notes, see below:
FOUR-PART STORY OF LIFE SERIES
Recent discoveries and insights in the life sciences, as well as geology, paleontology, geochemistry, and even astrophysics, have led to a radical new synthesis of the history of Earth and the life upon it.
Basically, the New Synthesis goes as follows: The Earth was formed from the debris left over from the formation of the solar system about 4,600 million years ago. Within about 100 million years, the embryonic Earth was struck by a planet about the size of Mars, resulting in the creation of the Moon. Outgassing from the cooling planet formed a primitive atmosphere with little or no oxygen. Another product of cooling was the differentiation of materials based on density and chemical properties, resulting in an iron-nickel core, a dense but deformable mantle, and a thin rocky skin, the lithosphere.
Surface temperatures eventually dropped to the point at which gaseous hydrogen dioxide (steam) was condensed out of the atmosphere to form the oceans. It was a mighty rain that outdid the 40-day Noachian flood of the Bible many millions of times over.
The erosive effects of rains over hundreds of millions of years created a rich chemical soup, resulting in the segregation of self-replicating molecules bounded within simple membranes, the first elemental life forms, around 3,900 million years ago or even earlier (no rocks older than 3,960 million years of age have been found to check for signs of life).
One theory currently in favor is that life may have appeared first in the chemically enriched environments around hot springs or at deep-ocean hot water vents, places where primitive anaerobic archaebacteria still flourish.
Once life got started, the great process of evolution took over, producing the overwhelming diversity of life that we see around us today. But it took a long time to progress beyond the unicellular bacteria. In fact, Earth was solely populated with bacteria and other primitive single-celled organisms for about three and a half billions years, nearly 80 percent of life's existence. (In many respects, these "lower forms" still rule our planet.)
The first microbes were anaerobic, a necessity since there was no free oxygen in the environment. But they produced oxygen as a byproduct of their metabolisms, eventually enriching the atmosphere with what to them was a toxic pollutant.
By 2,100 million years ago, enough free oxygen had accumulated in the atmosphere to form a protective ozone barrier to high intensity solar ultraviolet radiation, thus setting the stage for life to expand beyond the microbial and eventually onto the land itself.
The critical development of multi-celled oxygen-breathing organisms took place in the marine environment "only" about 540 million years ago, in what paleobiologists call the "Cambrian Explosion." In the space of a few tens of millions of years all the basic body forms that have come down to us evolved.
Plants, derived from algal bacteria, escaped the marine environment by evolving mechanisms to survive on land, thanks largely to a new partnership they forged with the fungi. And where plants went, herbivorous animals and their predators were sure to follow, thus creating our familiar terrestrial world.
Life scientists can only make rough estimates of the number of species now living on Earth -- ranging from 5 million to 30 million or more. Of these, only about 2 million species have been named, of which only a fraction have been studied enough to determine some of their basic biological and ecological functions. We know that some species are critical in maintaining our biosphere -- our home in space. The current reckless pace of extermination of species, the functions of many of which are unknown in maintaining the fabric of life, should be a subject of great concern for all of us.
The four-installment series may
be accessed via the following links
1. Earth's biogenic transformation (part 1).
2. Earth’s biogenic transformation (part 2).
3. Kingdom of Life: Bacteria.
4. Kingdom of Life: Fungi.
Click on the hyperlinks below to view the series:
(NOTE: These PDF files may take a while to open if you are using "dial up"...please be patient)