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Principles of Biology. By Frank H. Osborne, Ph. D. Evolution. The Heterotroph Hypothesis. According to the heterotroph hypothesis, the first organisms to develop were heterotrophs. The autotrophic organisms developed after the heterotrophic ones. Primitive Conditions on the Earth.
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Principles of Biology By Frank H. Osborne, Ph. D. Evolution
The Heterotroph Hypothesis According to the heterotroph hypothesis, the first organisms to develop were heterotrophs. The autotrophic organisms developed after the heterotrophic ones.
Primitive Conditions on the Earth The age of the Earth is thought to be 4.5 x 109 (4.5 billion) years. Evidence for this estimate comes from the measurement of the decay of Uranium. This time is divided into four eons. In the earliest eon, there was a reducing atmosphere, much heat, lightning (electrical discharge), ultraviolet (UV) light from the Sun and radiation.
Eons of Time EonDuration (Millions of Years) Hadian 4500-4000 Archaen 4000-2500 Proterozoic 2500- 600 Phanerozoic 600-Today
Primitive Conditions on the Earth There was no ozone layer in the earliest days of the Earth. To form an ozone layer requires oxygen. Oxygen is the waste product of photosynthesis. Photosynthesis did not develop until after the formation of the first eukaryotic cells, about 2.5 billion years ago. Therefore, without an ozone layer, UV light came all the way down to the surface.
Primitive Conditions on the Earth There are no rocks found so far that go back to the formation of the Earth. Geological processes of erosion, transport and depostion have worn away the original rocks. There have been rocks found in Canada and Australia that are dated in the range of 3.9 - 4.1 billion years.
Synthesis Reactions A reducing atmosphere of ammonia (NH3), methane (CH4), hydrogen (H2) and water (H2O) has been shown to be able to produce such molecules as urea, hydrogen cyanide, organic acids and other molecules under laboratory conditions by random synthesis reactions with each other.
Synthesis Reactions There was no oxygen in the early atmosphere but there was some CO2 present. The molecules produced experimentally in Miller's spark discharge apparatus were similar to biological molecules. For example, amino acids were found.
Aggregates of Organic Molecules Aggregates are collections of organic molecules that may have formed along the shorelines of primitive seas where the molecules were exposed to ultraviolet light. Radiation on rocks causes them to heat up. There is evidence that when organic molecules are heated together dry, they react.
Aggregates of Organic Molecules Fox took dry amino acids and heated them together. Water was released that condensed on the inside of the test tube at the top. This condensation resulted from reactions between the amino acid molecules. Thus the origin of the term "condensation reaction."
Coascervates Certain larger aggregates (coascervates) might have begun to divide after reaching a certain size. Experiments have shown that CH4, NH3, and H2O can yield bases like those found in DNA.
Anaerobic Respiration Fermentation is found in all cells, not only the anaerobic bacteria but even those that use aerobic respiration. So, anaerobic respiration must have developed first. The first organisms probably got their energy by fermenting organic molecules that were dissolved in the water.
Development of Autotrophs Some organisms must have developed the means by which to perform photosynthesis. The resulting release of oxygen over time led to the formation of the oxidizing atmosphere we have today.
Aerobic Respiration Those organisms that could tolerate and use oxygen went on to become aerobic. It is thought that eukaryotic cells developed as a result of one kind or prokaryote living inside another.
Endosymbiosis This explanation is called the endosymbiotic theory. According to this explanation, mitochondria that we have today were originally a form of prokaryote that had a knack for producing energy. Similarly, chloroplasts are thought to have resulted from other prokaryotes that could trap solar energy.
Endosymbiosis Evidence for this theory comes from the fact that mitochondria and chloroplasts have their own DNA molecules, independent of the DNA in the chromosomes of the nucleus of the cell. This DNA is closely related to bacterial DNA, not nuclear DNA.
Endosymbiosis Also, mitochondria and chloroplasts have their own ribosomes. These ribosomes are closely related to bacterial ribosomes and are distinctly different from the cytoplasmic ribosomes.
Geologic Time Scale Geologic Time Scale Geologic time is divided into eras, periods and epochs. Mainly the distinctions are based on fossil evidence.
The Geologic Time Scale Life began in the proterozoic eon, about 2.5 billion years ago. This is also known as the Pre-Cambrian era. Each era is a subdivision of an eon. Each era is also further subdivided into periods. The periods correspond to major divisions in geologic (and biologic) history.
The Geologic Time Scale Geologists use biology as evidence for different periods. Up until the discovery of radioactivity in 1895, there was uncertainty about the age of the Earth or different layers of rocks.
The Geologic Time Scale Geologists then and now use fossils to indicate information about the age and history of various rocks. The most recent period, the one we are in now, is known as the Quaternary Period.
Glaciations of the Quaternary • Others occurred beginning at 500,000 years and 250,000 years. The last one began at 70,000 years and ended 20,000 years ago. There were four major glaciations (ice ages) in the Quaternary period. The earliest ice age began 600,000 years ago.
The Fossil Record The oldest rocks are over 3.5 billion years old. Fossils are the remains of living things or are objects that were made by living things. These are left in sand or mud that will eventually be turned into sedimentary rock. Teeth and bones make good fossils as well as tools of primitive humans and worm burrows.
The Fossil Record In undisturbed rock layers, the oldest fossils (indicating the oldest rocks) should be found in the oldest layers. This is the case in the Grand Canyon that exposes approximately 2.5 billion years of Earth history in one place. Relatedness between fossils is based on comparative anatomy.
Early Mammals The first mammals came into existence as early as 1.5 x 108 (150,000,000) years ago. The earliest primates developed about 70,000,000 years ago. The earliest monkeys came into being some 40,000,000 years ago. The most primitive of them already had the same dental pattern as modern humans.
Fossil Record of Early Humans The oldest fossils are found in Africa. For human archeological sites, 14C-dating is used.
Fossil Record of Early Humans Information about the early ancestors of humans is derived from the study of fossil bones and skulls. In the early Miocene lived Proconsul. Proconsul may have been the common ancestor of chimpanzees, gorillas and humans. It is 25 million years old and had teeth like those of apes.
Early Pleistocene Hominids Early Pleistocene hominids lived in the old stone age. Australopithecus afarensis (southern ape of the Afar region of Africa) lived in east Africa at least 3 million years ago. [This makes it the earliest hominid.] It then evolved into the gracile A. africanus and the robust A. transvaaliensis at about 2 million years ago.
Early Pleistocene Hominids Gracile organisms have delicate boning whereas robust organisms have heavy boning. The robust ones lived for about 1 million years then died out. Humans are gracile. The gracile ancestors evolved into the genus Homo.
Early Pleistocene Hominids More recently in the Pleistocene lived Homo habilis. Homo is the genus that includes humans. All members of the genus Homo, other than Homo sapiens sapiens are extinct. Homo habilis, like Australopithecus was small but had distinct differences in the skull bones and teeth.
Middle Pleistocene Hominids Homo erectus had a more advanced Stone Age culture called Pre-Moustarian. It had the ability to use fire and create simple tools. Some specimens have been given names such as Java Man. Homo erectus developed in Africa about 1.6 million years ago.
Middle Pleistocene Hominids Homo erectus and Australopithecus lived in the same general areas of Africa and Europe. Australopithecus may have died out because Homo erectus was more advanced and could compete more easily.
Middle Pleistocene Hominids The earliest prototype Homo sapiens is dated at about 300,000 years ago. During the last ice age it evolved into two sub-species, Homo sapiens neanderthalis and Homo sapiens sapiens. Steinheim man is of the Neanderthal type. It has Mousterian culture which included ritual burial.
