General Biology 2: History of Life on Earth

General Biology 2 Prepared by Mr. Eugene C. Pansaon, LPT History of Life on Earth HOW OLD IS EARTH? The age of Earth is estimated to be 4.5 billion years old. The first widely accepted idea of how life on Earth formed was proposed by the Russian chemist Alexander Ivanovich Oparin (1894-1980) in...

General Biology 2 Prepared by Mr. Eugene C. Pansaon, LPT History of Life on Earth HOW OLD IS EARTH? The age of Earth is estimated to be 4.5 billion years old. The first widely accepted idea of how life on Earth formed was proposed by the Russian chemist Alexander Ivanovich Oparin (1894-1980) in the 1920s. He proposed that the atmosphere of early Earth was very reactive, with numerous incidents of lightning and high levels of ultraviolet radiation. Early oceans contained a solution of many essential elements and compounds referred to as “primordial soup”. Primordial Soup Theory The Origin of Life First Organic Molecules American chemists Stanley Miller and Harold Urey conducted an experiment in the 1950s in which they filled a flask with hydrogen, methane, ammonia, and water to represent the early atmosphere. Then, they passed electric sparks through the mixture to stimulate lightning. They discovered that several amino acids began to accumulate in their setup. First Organic Molecules How Life Began? Scientists believe that microscopic cell-like structures similar to modern bacteria appeared 200-300 mya. Protenoid microspheres - They had a selectively permeable membrane that allowed certain molecules to pass through them. - Had simple means of storing and releasing energy Where Did Life Evolve? Locations: - Soil surfaces - Interstellar space - Atmosphere Some scientists also suggest that life might have originated from the oceans, but complex organic molecule are vulnerable to damage due to the high sodium and chlorine concentration. Origin of Eukaryotic Cells Endosymbiosis is a type of relationship wherein an organism lives inside its partner. According the Endosymbiotic theory, eukaryotic cells created a symbiotic relationship with prokaryotic organisms. Paleontology The scientific study of the existence of life, including the origin and eventual destruction or extinction of different groups of organisms. Paleontologists specialize in studying the fossil remains, the ecologies of the past and the evolution of organisms. An example of a fossil record is Archaeopteryx lithographica from the late Jurassic period. It is said to have had many features of dinosaurs, which provide a strong evidence of the dinosaur ancestry of birds. Geology The scientific discipline that focuses on the study of rocks. Geologists are scientists who carefully study the different materials that make up Earth. Geologic Time Scale Calendar of events of earth’s history of life where they are arranged in chronological order. Scientists were able to develop it by studying rock layers and index fossils worldwide. Divisions of Geologic Time Scale Eons - Are the largest divisions in the geologic timeline. They are composed of hundreds of millions of years in duration. Phanerozoic eon, which began more than 500 million. Characterized by the existence of organisms that had skeletons or hard shells. Proterozoic eon (2.5 billion – 540 million years ago), where the first multicellular organisms rose and where mass extinction occurred. Archaeozoic eon (3.9 billion to 2.5 billion years ago) where the first life-forms represented by single-celled organisms appeared. Hadean eon (4.6 to 3.9 billion years ago), which is characterized by Earth’s formation from dust and gases. The Proterozoic, Archaeozoic, and the Hadean eons are collectively known as the PRECAMBRIAN TIME, which accounts for almost 90% of Earth’s History. Eras - Can be divided into smaller time intervals. Phanerozoic eon is divided into three eras, namely, Paleozoic, Mesozoic, and Cenozoic eras. Paleozoic era - Began about 540 million years ago and lasted for about 300 million years. This is when fossil records became rich with evidence of many marine organisms. Mesozoic era - Began about 200 million years – 180 million years ago. This era is called the Age of Reptiles and sometimes, the Age of Dinosaurs because this is when many kinds of dinosaurs existed. - Appearance of flowering plants. Mesozoic era Cenozoic era - Considered to be the latest era in the geologic timeline, which began from 65 million years ago up to the present. - Composed of Paleogene, Neogene, and Quaternary periods, which are characterized by the presence of primitive mammals and modern human civilization. - “Age of Mammals” Cenozoic era Periods - Are further subdivisions of eras. The Proterozoic eon is composed of the Vendian/Ediacaran period. - Life in this period only thrived underwater, and only few fossils existed because the animals were all soft-bodied. - The Paleozoic era has been divided into the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian periods. Cambrian Period - Organisms were noted to have hard body parts such as shells and outer skeletons. - The first known representatives of most animal phyla evolved during this period, which include jellyfishes, worms, and sponges. - Also common were the brachiopods, which were small animals with two shells. Cambrian Period These organisms resembled (but were not related to) modern clams. Hard-shelled segmented creatures called trilobites were the most dominant macroscopic life-forms in this period. A fossil of Modocia typicalis During the Ordovician and Silurian periods, early forms of cephalopods (which include octopi and squids) appeared. In the Devonian period, many plants, including ferns, adapted to drier areas, which allowed them to invade other kinds of habitats. “Age of Fishes” because many groups of fishes have evolved during this period. Life continued to expand on Earth’s surface during Carboniferous and Permian periods. The reptiles – animals with scaly skins that lay eggs with tough leathery shells – evolved from amphibians. a.) Life forms during the Carboniferous period b.) Skeletal fossil of Eryops The Mesozoic era was divided into the Cretaceous, Jurassic, and Triassic periods. These periods represent the age when many forms of dinosaurs are believed to have existed on Earth. Many organisms at the onset of the Triassic period survived the mass extinction during the Permian period, including fishes, insects, reptiles, and cone-bearing plants. Then, about 225 million years ago, the first dinosaurs appeared. One of the earliest dinosaur species belonged to the genus Coelophysis, which were meat-eaters. a.) A fossil of Coelophysis bauri b.) Flora and Fauna that existed during the Triassic period During the Jurassic period, dinosaurs became dominant animals on land for about 150 million years. - Dicraeosaurus was one of the largest dinosaurs in this period. - Archeopteryx, one of the earliest known birds, also appeared. The Cretaceous period is the time when reptiles were the dominant vertebrates on Earth. - During this period, several kinds of birds began to exist alongside Pterosaurs (flying reptiles). It was also the period when new kinds of dinosaurs evolved. - Iguanodon and Triceratops species emerged as common herbivores, and Tyrannosaurus rex and Spinosaurus were some of the dominant carnivores in this period. - The cretaceous period ended with a meteorite-caused mass extinction. Tyrannosaurus rex, one of the largest and fiercest carnivorous dinosaurs. A replicated fossil of Tyrannosaurus rex The Cenozoic era is divided into Tertiary and Quaternary periods. The Tertiary period is from 65 to 1.8 million years ago. During this period, Earth’s climate was generally warm and mild. Flowering plants emerged and grasses flourished, providing a vital food source that encouraged the evolution of today’s grass-eating mammals such as cattle, deer, and sheep. Fossil skeleton of Equus simplicidens The Quaternary period, on the other hand, is coined as the “Age of Man” because the earliest modern humans are believed to have existed at the start of this period. - From 1.8 million years ago up to the present and is characterized by a series of ice ages followed by warmer climates. - Then, about 20,000 years ago, Earth’s climate began to warm, causing the continental glaciers to melt, which resulted in the increase in sea levels. - Modern humans called Homo sapiens may have evolved as early as 100,000 years ago in Africa. A fossil of a male mammoth at the natural History and Mammoth Museum in Siegdorf located in Bavaria, Germany Epochs - Finer subdivisions shown in the Cenozoic era and parts of the Mesozoic era. - Our geologic timescale is an important tool that visually shows Earth’s history. With the help of this timescale, we can look at the past and identify the organisms that have existed a long time ago. Thank You!