Chapter 26 - Chapter 26 - The Tree of Life: An Introduction...

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Chapter 26 - The Tree of Life: An Introduction to Biological Diversity Chapter 26 The Tree of Life: An Introduction to Biological Diversity Lecture Outline Overview: Changing Life on a Changing Earth Life is a continuum extending from the earliest organisms to the great variety of forms alive today. Organisms interact with their environments. o Geological events that alter environments change the course of biological history. When glaciers recede and the land rebounds, marine creatures can be trapped in what gradually become freshwater lakes. Populations of organisms trapped in these lakes are isolated from parent populations, and may evolve into new species. o Life changes the planet it inhabits. The evolution of photosynthetic organisms released oxygen into the air, with a dramatic effect on Earth’s atmosphere. o The emergence of Homo sapiens has changed the land, water, and air at an unprecedented rate. Historical study of any sort is an inexact discipline that depends on the preservation, reliability, and interpretation of records. o The fossil record of past life is generally less and less complete the further into the past we delve. o Fortunately, each organism alive today carries traces of its evolutionary history in its molecules, metabolism, and anatomy. o Still, the evolutionary episodes of greatest antiquity are generally the most obscure. Concept 26.1 Conditions on early Earth made the origin of life possible Most biologists now think that it is credible that chemical and physical processes on Earth produced simple cells. According to one hypothetical scenario, there were four main stages in this process: 1. The abiotic synthesis of small organic molecules (monomers). 2. The joining of monomers into polymers. 3. The packaging of these molecules into protobionts, droplets with membranes that maintained a distinct internal chemistry. 4. The origin of self-replicating molecules that eventually made inheritance possible.
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The scenario is speculative but does lead to predictions that can be tested in laboratory experiments. Earth and the other planets in the solar system formed about 4.6 billion years ago, condensing from a vast cloud of dust and rocks surrounding the young sun. It is unlikely that life could have originated or survived in the first few hundred million years after the Earth’s formation. 1. The planet was bombarded by huge bodies of rock and ice left over from the formation of the solar system. 2. These collisions generated enough heat to vaporize all available water and prevent the formation of the seas. The oldest rocks on the Earth’s surface, located at a site called Isua in Greenland, are 3.8 billion years old. 1.
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Chapter 26 - Chapter 26 - The Tree of Life: An Introduction...

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