Historical Geology Understanding Our Planet\'s Past

marine life today. The first metazoans were a loose organization of individual cells united for a common purpose, such as locomo ...

Free ebooks ==> http://www.Ebook777.com The next evolutionary step was the jellyfish, which had two layers of cells separated ...

million years ago, however, no track-making animals existed. Marine worms burrowed into the bottom sediments or were attached to ...

tened bodies of many animals was the limited food supply available during the Proterozoic.A high ratio of surface area to volume ...

populations of widespread and diverse organisms. Sea levels rose and flooded large portions of the land. The extended shoreline ...

modern animals.The proliferation of these new organisms, representing nearly every major group of marine species, set the stage ...

The Ediacaran fossils represent a marine life very different from that of today’s oceans, including feathery fronds, puckered po ...

vendobionts, after the Vendian period, the final stage of the Precambrian, evolved a unique solution to the problem of growing l ...

In effect, biological activity was responsible for the iron deposits since photosynthetic organisms produced the oxygen. When pl ...

Free ebooks ==> http://www.Ebook777.com locked up in the sediments, the level of oxygen began to rise steadily, spawn- ing th ...

when massive sheets of ice nearly engulfed the entire landmass.The positions of the continents also had a tremendous influence o ...

overran nearly half the continents for millions of years. Four periods of glacia- tion occurred between 850 and 580 million year ...

Free ebooks ==> http://www.Ebook777.com is established that mimics both the 11-year sunspot cycle and the 22-year solar cycle ...

THE CONTINENTAL CRUST By the beginning of the Proterozoic, upward of 80 percent or more of the pre- sent continental crust was a ...

known for its widespread terrestrial redbeds, named so because sediment grains were cemented with red iron oxide. Their appearan ...

carbon dioxide concentrations in the Precambrian probably account for the prevalence of dolomite over limestone. These minerals ...

continents collided and closed an ancient ocean. Arcs of volcanic rock also weave through central and eastern Canada down into t ...

heated and erupted with volcanism.The warm, weakened crust consequently broke apart into several major continents between 630 an ...

T his chapter examines the invertebrate life-forms and landforms of the lower Paleozoic era. The Cambrian period from 545 to 500 ...

Free ebooks ==> http://www.Ebook777.com THE CAMBRIAN EXPLOSION The Cambrian was an evolutionary heyday for species, featuring ...