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Biology 110 - Basic Concepts and Biodiversity

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Antiquity of Life

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The available astronomical data indicate that the universe is about 13.7 billion years old. This estimate is based, in part, on the observation that the universe is constantly expanding. Astronomers have plotted the trajectories (directional movement) of various stars and galaxies and determined that all matter in the known universe arose from a common point. In an event often referred to as the "Big Bang," the universe arose in a relatively brief moment in time and matter was flung outward from this central origin. Since this beginning, this vast amount of matter has been hurling through space, undergoing a number of many changes as it traverses the cosmos. 

By using radiometric dating techniques (discussed herein) of pristine meteorites, astronomers have determined that our own solar system, along with the earth, formed 4.55 - 4.56 billion years ago.

The Hubble telescope was dispatched in 1990 to explore the far reaches of our galaxy and to photograph events (e.g., star formation). Astronomers use images captured by the Hubble telescope to further our understanding of the origin of the universe and solar systems.

 

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The atmosphere on early Earth was strikingly different from that of today. Primitive Earth's atmosphere consisted of methane, ammonia, hydrogen, water vapor, and a negligible amount of free oxygen. This is an important point because if there was a lot of free oxygen available, life probably could not have arisen from inorganic compounds. This is because oxygen tends to oxidize substances, which means that electrons are removed. Importantly, the early atmosphere was highly reducing (capable of gaining electrons and forming more complex molecules). Oxidation and reduction will be examined in more detail in Tutorial 23.

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Support for the Chemical Evolution of Life

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The Miller-Urey experiment has often been repeated, and similar set-ups have generated various organic compounds (including ATP when phosphate is added to the initial slurry). However, there are still various aspects about abiotic synthesis of organic compounds that stimulate much debate. For instance, many scientists feel that the essential ingredients for these early chemical reactions could have come from deep-sea vents in Earth's oceans or from submerged volcanoes, rather than from the early atmosphere. Also, the first cells might have been autotrophs, using inorganic sulfur and iron compounds to gain energy, rather than consuming organic molecules (heterotrophs).  Ultimately, these laboratory simulations give us insight into how the chemicals necessary for life could have formed. We will discuss the chemistry of life further in Tutorial 3.

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Early Earth

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Fossils are divided into age groups according to a geological time scale, a classification of different periods in Earth’s history. For example, layers of rock bearing evidence of the origin of most modern animal phyla would be classified as belonging to the Cambrian period in the Paleozoic era. We will discuss the Cambrian explosion in Tutorial 18. Layers of rock bearing fossils suggest a rapid diversification of reptiles took place during the Permian period in the Paleozoic era. 

While you will not need to know the different periods and epochs for this course, you should be familiar with the four great eras of the geological time scale: Precambrian (oldest), Paleozoic (Figure 5), Mesozoic, and Cenozoic (Figure 6); and you should know that we are currently in the Quaternary period of the Cenozoic era. 

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Early Geological Eras

Recent Geological Eras


Figure 4. The Precambrian and Paleozoic Eras. 
(Click to enlarge)


Figure 5.  The Mesozoic and Cenozoic Eras.
(Click to enlarge)

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The Earth has been a living planet for about 4 billion years.  During that time, life has evolved and diversified into the approximately 1.8 million species that have been described so far, with the possibility of between 10 and 100 million species living on the planet today.  All life on Earth appears to have arisen from a single common ancestor based on the evidence that all organisms studied so far use virtually the same genetic code to transform the information in their DNA into proteins  (we will cover this in Tutorial 35). proteins.  Life has diversified into three major domains, the Bacteria, Archaea, and Eukarya.  The Bacteria and Archaea have more simple cells (prokaryotes), while member of the Eukarya have complex cells with a nucleus and an array of organelles that perform different functions within the cell (eukaryotes). Figure 9 shows the relationships among these groups. 

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Figure 9. The Three-Domain System of Classification. (Click to enlarge)

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Questions?  Send your instructor a message through ANGELCanvas?

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