Origin-07-web - Lecture 1 1 Lecture 1 Origin of Life The...

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Lecture 1 Lecture 1: Origin of Life The Time-Scale of Life How old is the earth? Geologists and astrophysicists believe the earth is roughly 4.6 billion years old. Geologists base their estimates on measurements of radioactive decay of uranium to lead in rocks. A brief overview of the history of life: < Figure 26.9 > The geological time scale is separated into eras. The eras are the Precambrian, the Paleozoic, the Mesozoic and the Cenozoic. The Precambrian lasts from the beginning of the earth 4.6 billion years ago to roughly 543 million years ago. The Paleozic lasted from roughly 543 to 250 million years ago. The Mesozoic lasted from 250 to 65 million years ago. The Cenozoic has lasted from 65 million years ago to the present. Periods are ontained within eras. An examination of the geological time scale reveals some interesting features. For example, the first fossils are dated around 3.6 to 3.8 billion years ago, roughly 1.0 billion years after the formation of the earth. There weren’t any multicellular animals for another 2.6 billion years; animals first evolved roughly 700 million years ago. Plants first invaded land around 440 million years ago. Humans are remarkably recent - we’ve arisen in the last 100,000 years (and even more recently by some estimates) Time table of important events in the earth’s history: Event Approximate Age Origin of Earth 4.6 billion years ago Earth cools and crust solidifies 4 billion years ago First evidence of life/origin of life 3.6-3.8 billion years ago Oldest prokaryotic fossils 3.5 billion years ago Accumulation of oxygen in the atmosphere 2.5 billion years ago Origin of Eukaryotes 2 billion years ago Origin of multicellular organisms 1 billion years ago Plants and fungi colonize land 440 million years ago First Mammals 190 million years ago First humans 100,000 years ago 1
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Lecture 1 This discussion underscores the point that most of the organisms on which we focus - i.e., birds, mammals, trees, fish - originated quite recently relative to the first origins of life. Essay, p. 15, if the history of the earth were reduced to a year, 1 day would be 12.6 million years, 1 second would be 143 years, and humans evolved on Jan. 31 about one hour before midnight! The vast majority of the earth’s history has been dominated by single-celled organisms. Life is still dominated by single-celled organisms. The Origin of Life Before we speculate on how life began, we need to know a little something about the conditions on earth during and after its formation.
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