BES 108D Lecture 3 PDF - Organisms in Their Environment

1 BES 108D Lecture 3 13th Jan 2025 Organisms in their environment By Dr. Benazir Alam ([email protected]) Copyright © 2025 Pearson Canada, Inc. 25 - 1  2 Chapter 25 The History...

1 BES 108D Lecture 3 13th Jan 2025 Organisms in their environment By Dr. Benazir Alam ([email protected]) Copyright © 2025 Pearson Canada, Inc. 25 - 1  2 Chapter 25 The History of Life on Earth Continued…….. Copyright © 2025 Pearson Canada, Inc. 25 - 2 Radiometric Dating A living organism contains the most common carbon isotope, carbon- 12, as well as a radioactive isotope, carbon-14. When the organism dies, it stops accumulating carbon-14, and the amount of carbon-12 in its tissues does not change over time. However, the carbon-14 that it contains at the time of death slowly decays into another element, nitrogen-14. By measuring the ratio of carbon-14 to carbon-12 in a fossil, we can determine the fossil’s age. Radiocarbon dating can be used to date fossils up to 75,000 years old To date older fossils, ages of sediments in sedimentary rocks are considered. If two volcanic layers surrounding fossils are found to be 525 million and 535 million years old, for example, then the fossils are roughly 530 million years old. Copyright © 2025 Pearson Canada, Inc. 25 - 3 How Rocks and Fossils Are Dated Absolute ages of fossils can be determined by radiometric dating – A radioactive “parent” isotope decays to a “daughter” isotope at a characteristic rate – Each isotope has known half-life, the time required for half of the parent isotope to decay which is not affected by temperature, pressure, or other environmental variables – Carbon-14 has a half-life of 5730 years. This means that after 5730 years, half of the original amount of Carbon-14 in a sample will have decayed. – The half-life of a radioactive isotope does not depend on its mass. Regardless of the amount of the material present, the half-life remains constant. For example, whether you have 1 gram or 100 grams of a radioactive substance, it will still have the same half-life. Age=Number of half-lives×Half-life duration Copyright © 2025 Pearson Canada, Inc. 25 - 4  A rock started with 1000 atoms of a particular parent radioactive isotope and now has 750 daughter isotopes. If the half-life of this isotope is 500,000 years, how old is the rock? After 1 half-life, the rock will have 500 daughter isotopes After 2 half lifves, the rock will have 500+250=750 daughter isotopes So, no. of half lives the radioactive isotope has undergone=2 Age=Number of half-lives×Half-life duration =2 X 500,000=1000,000 i.e. Pearson Copyright © 2025 1 million year Canada, Inc. 25 - 5  Oxygen Revolution The initial rise in O2 was likely caused by oxygenic photosynthetic prokaryotes Later increases in atmospheric O2 might have been caused by the evolution of eukaryotic cells containing chloroplasts This “oxygen revolution” from 2.7 to 2.4 billion years ago caused extinction of many anaerobic prokaryotic groups Some groups survived and adapted using cellular respiration to harvest energy Copyright © 2025 Pearson Canada, Inc. 25 - 6  7 The Geologic Record Copyright © 2025 Pearson Canada, Inc. 25 - 7 The Geologic Record Copyright © 2025 Pearson Canada, Inc. 25 - 8 The Rise and Fall of Groups of Organisms Reflect Differences in Speciation and Extinction Rates The history of life on Earth has seen the rise and fall of many groups of organisms The rise and fall of groups depends on speciation (a process by which new species arise via geographic isolation, reproductive isolation, or adaptation to different ecological niches) and extinction (a process by which species cease to exist due to habitat loss, climate change, competition, predation, and human activities) rates within the group Just as a population increases in size when there are more births than deaths, the rise of a group of organisms occurs when it produces more new species than are lost to extinction Copyright © 2025 Pearson Canada, Inc. 25 - 9 How Speciation and Extinction Affect Diversity Extinct Lineage “B” has greater diversity than lineage “A” Copyright © 2025 Pearson Canada, Inc. 25 - 10  Plate Tectonics (1 of 2) Cutaway view of Earth At three points in time, the land masses of Earth have formed a supercontinent: 1 bya, 600 mya, and 250 (Pangaea) mya According to plate tectonics theory, Earth’s crust composed of plates floating on Earth’s mantle Movements in the mantle cause the plates to move over time in a process called continental drift. Oceanic and continental plates can collide, separate, or slide past each other Interactions between plates cause the formation of mountains and islands, and earthquakes. 45 million years ago, when the Indian plate crashed into the Eurasian plate, starting the formation of the Himalayan mountains. Copyright © 2025 Pearson Canada, Inc. 25 - 11  Consequences of Continental Drift Continental drift has many effects on living organisms – A continent’s climate can change as it moves north or south – Separation of land masses can lead to allopatric speciation, which occurs when populations of a species become geographically isolated from one another. This geographic isolation can prevent gene flow between the populations, allowing them to evolve independently over time. As a result, they may develop distinct traits and eventually become separate species.. Evidence of Continental Drift The distribution of fossils and living groups reflects historic movement of continents – For example, similarity of fossils in parts of South America and Africa is consistent with the idea that these continents were formerly attached Copyright © 2025 Pearson Canada, Inc. 25 - 12 Mass Extinction Events A number of factors might have contributed to the mass extinctions, including: – Intense volcanism in what now is Siberia – Global warming and ocean acidification resulting from emission of large amounts of CO2 from volcanoes – Lower oxygen concentrations resulting from nutrient enrichment of ecosystems – Meteorite (containing iridium) impact. Dust clouds blocked sunlight and disturbed global climate. This particularly happened in the Mesozoic era when the dinosaurs survived. Copyright © 2025 Pearson Canada, Inc. 25 - 13  14 The big five mass extinctions The extinction event that led to the demise of the dinosaurs, known as the Cretaceous- Paleogene (K-Pg) extinction event, is considered one of the largest mass extinctions in Earth's history. It occurred about 66 million years ago Copyright © 2025 Pearson Canada, Inc. 25 - 14  15 Extinction of dinosaurs! ❑ The crater associated with the mass extinction event of the dinosaurs is called the Chicxulub crater. ❑ It measures 180 km across ❑ It is located on the Yucatán Peninsula in Mexico and is believed to be the result of a Buried massive asteroid impact around 66 million years ago Copyright © 2025 Pearson Canada, Inc. 25 - 15 Is a Sixth Mass Extinction Under Way? Scientists estimate that the current rate of extinction is 100 to 1,000 times the typical background rate Extinction rates tend to increase when global temperatures increase Factors such as deforestation, habitat destruction, overhunting, overfishing, global warming would contribute to mass extinction. Data suggest that a sixth, human-caused, mass extinction is likely to occur unless dramatic action are taken Copyright © 2025 Pearson Canada, Inc. 25 - 16  17 What would be the factors favouring a sixth mass extinction? Copyright © 2025 Pearson Canada, Inc. 25 - 17