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Molecular phylogenetics places the animals firmly within the clade of the Opisthokonta, with the choanoflagellates as their most likely sister group. Choanoflagellates possess many of those cell-adhesion and cell-cell signalling molecules that are required for multicellularity. These molecules thus largely predate the evolutionary transition from single cells to multicellular organisms. Palaeontological evidence of the earliest stages of metazoan evolution is either lacking or problematic. Late Precambrian fossils include a diversity of macroscopic forms (often known as the vendobionts) whose phylogenetic relationships to modern metazoans are disputed, and a number of recently described embryos from the Chinese Doushantuo deposits, probably corresponding to adults organisms of minute size. Fossil evidence still supports the concept of a quite sudden Cambrian explosion of animal diversity. Molecular estimates of the timing of divergence of the main metazoan lineages mostly point to ages quite than the base of the Cambrian, but those results are not consistent overall.

This chapter looks at climate change in the broader planetary sense. It examines evolutionary process in planetary atmospheres, with an application to the modelling of the evolution of the Earth's climate from the Precambrian to the present time. It examines the comparative climatology of the terrestrial planets and looks at the atmospheres of the giant planets. The photochemical and climate modelling techniques developed in the earlier chapters is then applied to Titan's haze formation and atmosphere. A brief look is given to extrasolar planets.

The geological history of California provides the basis for its present geological complexity. The position of California along the continental margin gives a physical context that began when the earth’s crust was formed and has resulted in rapid geological change and effective biotic isolation from much of North America. Chapter 2 begins in the early Proterozoic and describes the changes to the area of the earth currently known as North America through the Mesozoic.

This chapter discusses the three main techniques for recognising when eukaryotes first appeared. Each technique, however, gives different answers, with its own set of problems. The most obvious source of evidence is the fossil record, especially of macroscopic and multi-cellular life, which now extends back into the Precambrian. The fossil record of the earliest eukaryotes is inevitably indistinct, but a different kind of fossil can help to date the origins of eukaryotes – the so-called ‘molecular fossils’. A third and last approach to dating the emergence of eukaryotes uses what have come to be called molecular clocks, where the molecules in question are DNA or RNA, or the proteins they encode.

This chapter describes Australian paleontologist Reginald Sprigg's discovery of the famous Ediacaran fauna in 1946. It argues that Sprigg's discovery helped pave the way for Precambrian paleobiology and that his case illustrates the sometimes tortuous path of ideas to scientific acceptance. This chapter explains that the findings of Sprigg were not accepted until their later appropriation by Charles Walcott in his work at Burgess Shale.

This chapter discusses the author's own personal experience in witnessing the growth of Precambrian paleobiology. It relates how the assumptions accepted by early workers influenced the development of this science and how and by whom breakthrough advances were brought to the fore in the mid-1960s. This chapter discusses the pioneering works of John William Dawson, Charles Doolittle Walcott, and Albert Charles Seward. It also narrates the story of the gradual expansion of the fossil record over the past several decades, including the discovery of microfossils dating some 3.5 billion years old.

The way the planet has changed through geologic time, and life on it, the account of the Earth, is the topic of this and the next three chapters, starting in this chapter with the Precambrian Supereon. The overarching principles of geologic time, plate tectonics, and evolution worked dynamically to create the biography of the planet. This chapter traces back to the recesses of the geologic record and early Earth, from its birth and the formation of the Moon through seven-eighths of its existence, a huge span of time. Early life forms emerged during this supereon in the Archean Eon and had a profound influence on other Earth systems. Life interacted and changed the chemistry of the atmosphere through photosynthesis, so much so that the changes are thought to have sent planetary systems over an edge into multiple “Snowball Earth” episodes when most of the planet froze over. In addition to the beginning of organic life and climate, the emergence and configuration of the continents during the Precambrian are covered. Events of this supereon set the stage for the burgeoning of life forms in the next eon, the Phanerozoic.

In just a few years, the magnetic bar-code secreted beneath the world’s oceans had provided detailed intelligence on the motions of the plates. When combined with other data from the sea floor, this allowed geophysicists to reconstruct the history of entire ocean basins following the rifting of Pangea. Some folk, however, are never happy, and ‘glass-half-empty’ types might well have complained that, impressive as all this was, it accounted for less than 200 million of the 4500 million years of Earth history, i.e. just 4%. What about that other 96%? Did plate tectonics operate through part or all of this long history and, in any case, how could you ever know, since the evidence had all been shredded by the closure of earlier oceans? There was hope: the same process that had so conveniently sequestered the recent history of the plates in the sea floor had also been at work throughout much of earlier geological time, recording the story in rocks onshore. By comparison with the high-definition picture of plate motions offered by bar-codes and fracture zones, this recording was monochrome, fuzzy, and incomplete. Yet, by the mid-1950s, it had already provided conclusive evidence that continents were truly mobile. Curiously, hardly anyone noticed.

Granitic rocks represent the dominant part of the Precambrian continental crust and have characters different from younger granites. Methods for and the significance of age determinations are briefly reviewed. The Archaean TTGs (tonalites, trondhjemites and granodiorites) are examined with respect to their geochemistry, petrogenesis and setting, namely subduction environments or others, and exemplified by the melt products of the Barberton (South Africa) amphibolites. Late-Archaean potassic granitoids and sanukitoids, Proterozoic granitoids (Eburnian from West Africa, AMCG (anorthosite–mangerite–charnockite–granite) associations from Finland and Norway, etc.) and granitic rocks derived from impacts are examined in some detail. Sections include those on age determination, Archaean TTG granitoids, late-Archean granitoids, Proterozoic granitoids and impact granites, including the Sudbury igneous complex.

As we apprehend the likelihood of an almost inconceivable cosmic impact occurring again at some time in the future, it is worth considering how we got to be here in the first place. The quest for an explanation of our origins is, of course, as old as the ability of humans to conceptualize questions and consider answers. Our species has probably been able to do that for hundreds of thousands of years, since well before evidence of its ability to comprehend was etched in cave paintings, perhaps back in an age when stone tools began to be patiently chipped out of flint rock. But when questions about origins were first hesitatingly formulated, answers could only be invented. There was no way any human beings could have known back then what we know now about the nature of the universe and its contents. Our collective ability to understand the world in which we live received an enormous impetus starting about 400 years ago when the scientific method for approaching reality was first practiced. That was when it was discovered that through experiment and observation, and above all through measurement, it became possible to unravel the secrets of the universe. That was when Galileo first pointed a telescope at the heavens, William Gilbert experimented with natural magnets, and Johannes Kepler discovered the laws of planetary motion. Since then, our species has gathered a stunning new perspective on the nature of this universe and its origins, a perspective that has relegated to the back burner of human thought most of the fantasies that have so long held sway over the human mind. As a result of the high technology that has emerged during this century, scientists have learned to probe into the depths of matter and into the farthest reaches of space. In the course of this exploration, astronomers, in particular, have learned that the universe has its roots in awesome violence and that the birth of the earth and moon were accompanied by what, from our perspective, would be considered catastrophic events. Were anything remotely similar to occur today, all life on earth would be instantly terminated.

Most of the important metal ores in medieval and ancient times were pyrite-rich sulfides. These pyrite-rich ores were a major source of a suite of valuable commodities such as sulfur, arsenic, copper, lead, zinc, and nickel, as well as some gold and silver. This is why in 1725 Henckel could devote a 1,000-page volume to pyrites, sensu lato. Because of its relative abundance, its potential economic importance, and its exotic composition compared with the rock-forming minerals, pyrite has played a key role through the ages in developing ideas of how minerals and ore deposits form. During the last century, pyrite became an even more important mineral in discussions of ore genesis because it is also a key component of sediments. This led to conflicting theories of ore genesis, in which the ore minerals were formed in the sediments or introduced later, often by processes related to volcanism. The conflict between adherents of these theories continues to this day. Pyrite constituted a key, but sometimes uncomfortable, mineral in ancient theories of mineral formation. It was relatively common and often economically important. However, it contained sulfur as a key constituent and this contrasted it to many other common minerals and rocks in that this meant that pyrite could be changed by heating. Heating released sulfur from pyrite, leaving a residue of stony slag. The ancients also recognized sulfur as a special material since it occurred in solid, liquid, and gaseous form, rather like water. Any theory of mineral formation needed to explain how this protean element got into pyrite. This problem was compounded by the fact, discussed in Chapter 3, that for some unknown reason the ancients did not know that pyrite contained iron. Ancient theories of mineral formation divide into three categories: (a) the Genesis theory: that all minerals were formed by God during the creation of the Earth; (b) the Aristotelian theory: that all minerals were formed at depth in the Earth through the interactions of the four basic elements; and (c) the Alchemical theory: that minerals were formed from combinations of mercury and sulfur.