notes about the biology readings
Chapter 8 explosion of animals
Charles Doolittle Walcott:mark his crowning discovery on that Canadian mountain peak—trilobites.
•of the greatest mysteries in paleontology: the so-called Cambrian explosion—the apparently sudden emergence of large, complex animals in the Cambrian period over 500 million years ago.
•this nearly 60-year-old veteran geologist discovered one of the oldest and most important mother lodes of animal fossils ever unearthed.
-Walcott rose to be the director of the U.S. Geological Survey, secretary of the Smithsonian Institution, a founder of the Carnegie Institution of Washington, and president of the National Academy of Sciences.
•Walcott later published his first paper in a scientific journal, the Cincinnati Quarterly Journal of Science, describing a new species of trilobite.
•grand” total of 25,000 vertical feet surveyed—probably the largest section ever measured by a single geologist in the 19th century.
•Cambrian fossils was in fact laid down during an immense period before the Cambrian—during the Precambrian era. The fossils he had found within it were the first clear evidence of Precambrian life and included structures now called stromatolites, formed by mats of ancient single-celled blue-green bacteria (cyanobacteria), and remains of large algae
Roosevelt’s and Walcott’s passions converged most strongly on the matter of conservation. Walcott was frequently summoned to the White House for conferences about forests, rivers, parks, and politics. Concern that the United States lacked adequate laws to protect prehistoric artifacts, cliff dwellings, cemeteries, caves, mounds, and other sites, as well as areas of scientific or scenic value, helped forge the Antiquities Act of 1906. It empowered the president to set aside as a national monument, or park, whatever lands he deemed necessary for their preservation. One of the first areas Roosevelt designated as a national monument was the Grand Canyon (1908).
Walcott thought that the fossils were 15 to 20 million years old. We now know that they are much, much older—the Cambrian period began 543 ± 1 million years ago—and that the Burgess fossils are about 505 million years old. The Precambrian rocks in which Walcott found a few fossils were formed 700 million to 1.2 billion years ago.
Chapter 7 Great Minds think a like
CAMBRIAN
GEOLOGY AND PALEONTOLOGY
II ABRUPT APPEARANCE OE THE CAMBRIAN FAUNA ON
THE NORTH AMERICAN CONTINENT Walcott
limit paleontological conclusions to results obtained from studies of material from the oldest fossiliferous Cambrian rocks.In summing up the Lower Cambrian fauna in 1891
That the life in the pre-Olenellus seas was large and varied there can be little, if any, doubt. The few traces known-of it prove little of its character, but they prove that Hfe existed in a period far preceding Lower Cambrian time, and they foster the hope that it is only a question of search and favorable conditions to discover it.
western side of the Rocky Mountains in the United States and on their eastern (western) slopes in British Columbia. There the great thick- ness of conformable pre-Olenellus zone strata p
western interior or Cordilleran-areas, are of terrigenous origin, and in the absence of a marine fauna are considered as having been deposited in epicontinental seas or lakes of fresh or brackish water.
including "the major part of the pre-Cambrian sedimentary rocks, though it also contains sedi- ments so deformed and metamorphosed that their stratigraphy cannot be deciphered.
Sources of Sediments.—Of the sources of the sediments of the Algonkian (Proterozoic) formations of the Lake Superior region,
Chamberlin and Salisbury consider [1906, Vol. 2, p. 199] "that a large portion of the sediments was produced by mature decomposition of older rocks, and this implies that they were not derived by
rapid mechanical abrasion such as that which accompanies and fol- lows great elevation and excessive precipitation.
if deposited in the ocean, would probably have been accumulated in deep, quiet water [Chamberlin and SaUsbury, Vol. i, 1904, pp. 361-363], but
(a) the large amount of calcareous matter ; (b) the presence of shrinkage cracks and ripple markings on shales, sandstones, and
limestone shales; (c) the presence in calcareous shales of fossils that lived in shallow water [Walcott, 1899, pp. 235-238],
will first call attention to the origin of the great series of Tertiary terrestrial non-marine sediments in the western section of the continent, for the solution of that problem has a most important
bearing on the probable origin of the Algonkian sediments.
At the time of the
Tertiary deposition there was abundant life, both on the land and in the water, but in Algonkian time only a fragment of the pre-Cam-
brian life had had the opportunity of adapting itself to the conditions
of the inland seas of late Algonkian time.
Dr. Joseph Barrell has given a full review of the evidence favor-
ing the continental origin of most of the Algonkian rocks of the
Cordilleran area. He argues that from the presence of mud-cracks in the Belt and Grand Canyon series that many of the formations were deposited on flood plains is thus seen that the interval between the Algonkian and Cambrian was at least long enough to permit dynamic movements and chemical changes to effect considerable results, even before the period of erosion and reduction began.
pre-Cambrian land surface was formed of sedimentary, eruptive, and crystalline rocks that did not in any known instance immediately precede in deposition or origin the Cambrian sediments
The known fossils contained in the Algonkian sediments of the Cordilleran geosyncline lived in fresh or brackish waters that were rarely in connection with marine waters on the margins of the Algonkian continent of North America. This will explain the abrupt
appearance of a highly specialized crustacean deep down in the Belt series.
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