Ever wonder how life began ex nihilo, out of nothing? Cradle of Life, The Discovery of the Earth's Earliest Fossils, presents the most current thinking along these lines. This 367 page 1999 Princeton University Press volume by J. William Schopf retails for $29.95. I special ordered my copy through Barnes and Noble and received their 10% discount on hard cover books. Cradle of Life is well illustrated with diagrams and both color and black and white photographs.
Schopf begins this twelve chapter book with introductory information about geologic time, plate tectonics, early discoveries and early interpretations. More modern "early" discoveries and "recent" modern interpretations from new evidence and new scientists beginning in the 1950's follows.
Schopf answers numerous questions that a reader would be likely to ask. Revealed is the slim likelihood that any living organism will end up as a fossil (More than 99.9% of everything that has ever lived on earth is recycled into other living organisms - less than .1% become fossils). Add to this that the older the fossil sought after, the less likely that the correct age of rocks survive (Geologic processes erode, metamorphose, and destroy rock units through plate tectonics). No sedimentary rock on the earth is older than 3,500 Ma (millions of years before present = 3.5 billion years ago). With these facts considered, there are very few places on earth with surviving sediments available for investigating. The geologic age of these sediments is explained including the methods used to determine that age. Another problem to resolve is whether the find is a fossil or an inorganic deposit. Despite these hurdles, fossil "bacteria" have been discovered in the 3,465 Ma Australian Apex Chert.
By the fourth and fifth chapters Schopf departs briefly from fossils to give the reader a background in the biology of life. Some readers may find these chapters to be more difficult reading. In order to understand biology one needs to understand the chemistry of life. Schopf has done an excellent job of simplifying this material but it necessarily includes chemical symbols, molecular symbols and chemical reaction formulae. Those who have never seen a chemistry class may find this difficult to understand. These chapters include discussion of the building blocks of life - one building upon the other from organic molecules called nucleotides to RNA and DNA.
The next chapters should impress the reader with the evolutionary process and why learned scientists call evolution a fact. Cradle of Life reveals to the observant reader that all life on earth is based upon the four chemical elements of Carbon, Hydrogen, Oxygen, and Nitrogen (CHON). Numerous laboratory experiments have been done over the years simulating the chemical makeup of the early earth along with the prevailing environmental conditions. Each of these experiments has produced various forms of the building blocks of life. The beginnings of life can be formed by simple chemical compounds placed together under the right conditions. From this start, the building blocks join to form higher level compounds again by chemical reactions. This process proceeding over millions of years eventually led to biological cells. Schopf takes the reader through these steps explaining how these compounds replicate and develop metabolic processes.
Chapter Six explains the most fascinating evidence of the atmospheric oxygen content of the early earth. The major source of the world's iron is in Banded Iron Formations. [Australian samples of this material have been available from dealers at the annual Gem and Mineral Show.] It appears as straight or wavy parallel bands of black alternating with red. The banding is from seasonal deposition of iron rich and iron poor sediments. The black is hematite, a different form of iron oxide than the more familiar "rust" we all know. Simplistically, free iron in solution (in the oceans) can not exist in the presence of oxygenated water. Therefore, during the time of deposition of banded iron formations, minimal free oxygen existed in the oceans (this ocean oxygen has to come from the air meaning there was minimal oxygen in the atmosphere as well). Further, at the time that banded iron deposition ceased, the oxygen levels in the atmosphere and oceans was such that free iron was immediately dropped out as red "rust" just as it is today. The beginning and end of banded iron deposition on earth is dated to 3,500 Ma to 2,000 Ma. The significance in all this is the source of the oxygen - photsynthesizing cyanobacteria concentrated in lagoonal environments. The early forms of cyanobacteria existed as slimy mats. You may know them better as one of the life forms responsible for Stromatolites. Schopf presents a more detailed explanation in Cradle of Life.
The seventh chapter marks the return to discussions of early life in the form of the aforementioned Stromatolites. The cyanobacteria form the top photosynthesizing layers of the Stromatolite. Other anaerobic "bacteria" form lower layers. These plus influx of sediments produce the distinctive layered configuration of Stromatolites. Many of the nature programs will show the mound shaped Stromatolites in Shark Bay in Australia.
Cradle of Life continues with the evolution of higher forms in the following chapters. Cells with nuclei may have existed as early as 2,800 Ma. Better proof but still not certain is found in 2,100 Ma rock. Firm evidence comes in at 1,800 Ma rocks from China.
Solution To Darwin's Dilemma is the topic in chapter ten. "Darwin's Dilemma" was not whether evolution had occurred but where was the proof of the earliest life forms that should have existed prior to the Cambrian? Darwin proved that evolution had occurred by factual evidence; remember that the multiple "theories of evolution" are proposals on the mechanism of how evolution (the fact) works. [Unfortunately, incomplete science education and the popular press have the fact and the theories confused]. Schopf does an excellent job explaining this starting with how science is done. He ends with a logical explanation of the evolution of intelligence.
Cradle of Life ends with a chapter illustrating examples of early mistakes and hoaxes in science. One of these very famous fossils was Homo diluvii testis - "Man a witness of the deluge". Discovered and described by Johann Jacob Scheuchzer in 1725, the fossil fit with prevailing religious beliefs and was seen as providing proof of Biblical Truth (the Noachian flood). Georges Cuvier showed this to be a 15 Ma fossil salamander 100 years later. The important premise to remember from this chapter is that science can make mistakes but sooner or later they are corrected. Science is a self correcting discipline.
Finally, Cradle of Life deals with Martian meteorites and possible proof of life on Mars. You'll find this interesting from the aspect of political pressures and government funding. It will certainly open your eyes to the veracity of facts as presented in the daily news.
Cradle of Life has an excellent Glossary and a chapter by chapter guide to recommendations for Further Reading.
I strongly endorse Schopf's Cradle of Life for many reasons. There is a tremendous amount to be learned from the search and discovery of the earliest forms of life on earth. Besides the main thrust concerning life Schopf well illustrates the methods of science, the intertwining of chemistry and biology, and the role of evolution.
