Geological Time Scale PDF

GEOLOGIC TIME SCALE (REVIEWER) ❖ This refers to a system of dating the history of Earth in a chronological manner using geological data. ❖ It is divided into eons, eras, periods, and epochs. EONS – refers to the greatest expanse of time divided into the Phanerozoic and Precambria...

GEOLOGIC TIME SCALE (REVIEWER) ❖ This refers to a system of dating the history of Earth in a chronological manner using geological data. ❖ It is divided into eons, eras, periods, and epochs. EONS – refers to the greatest expanse of time divided into the Phanerozoic and Precambrian eons. The Phanerozoic eon (542 million years ago) means ‘visible life’ that was constructed through rock units that bear abundant fossils. The Precambrian eon (4 billion years ago) represents the period between the birth of the planet and the appearance of life forms. ERAS – eons are subdivided into eras. Phanerozoic eon is divided into three eras namely Paleozoic, Mesozoic, and Cenozoic era. These eras are subdivided into periods, and PERIODS are subdivided into EPOCHS. Arranged from older to recent time: EONS Hadean Formation of gas and dust 4.6 billion years ago On the earth’s surface, the ocean was built of boiling sulfur due to erupting volcanoes Blasting of rocks and asteroids from space There is no atmosphere, instead, air formed thick and steamy layers of dust and crud. The sky was mostly filled with carbon dioxide, water vapor, nitrogen, and sulfur compounds. As of today, there are still no fossilized rocks found from this eon. Archean/Archaean Began about 1 billion years after the formation of Earth. Earth mostly cooled down and the water vapor from the air condensed and formed the global ocean. The abundant carbon dioxide in the air chemically changed and formed limestones that were deposited at the bottom of the ocean. The atmosphere started to form and was mostly composed of nitrogen. The melted rocks cooled down and formed the ocean floor. Earth’s interior was still hot and active. This caused a series of volcanic eruptions and formed long chains of small islands. The continents still have not formed at this time. Small landmasses were present, however, and were formed through the movement of rock deep in Earth's interior towards the surface. Small islands collided and formed larger islands, eventually creating the continental cores. Cratons – are large areas of the continental lithosphere that were formed as early as Precambrian. Cyanobacteria – also known as blue-green algae, first organisms known to have produced oxygen. Proterozoic It started about two billion years after Earth was formed.  Earth was suspected to have two supercontinents: one was located in the equator while the other one was situated on the other side. These were formed due to the collision of islands from the previous eons. Earth's interior continuously cooled down and fewer volcanoes were active. Plate tectonics, or the movement of Earth’s landmasses, was still active and frequent. The multicellular organisms in the form of algae in the ocean started to free oxygen that bonded with chemical elements such as iron to form great mineral deposits around the world. Earth in this era was very cold with bluish glacial ice sheets. Phanerozoic Recent eon and divided into different eras. The first era is Paleozoic. PALEOZOIC ERA At the start of this era, the world-continent Pannotia was broken into pieces leading to the formation of Pangea that makes Earth's continents connected once again. This era is mainly characterized by the explosion of different life forms that started to emerge on Earth The Paleozoic is divided into six periods: the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. Cambrian period The explosion of life occurred. The first multicellular animals, also known as Ediacarans, appeared in the fossil record that was dated almost 600 million years ago. Ordovician period Dominant animals were marine invertebrates such as trilobites and corals. Silurian period It is marked by the first appearance of land plants. Devonian period It is also known as the Age of Fishes. Massive forests of progymnosperms, such as Archaeopteris became highly abundant. Carboniferous First seed plants and first reptiles appeared. period Carbonate deposition was dominant and was mostly present on landmasses. Permian period Earth's crustal plates formed a single, massive continent called Pangaea. It is marked by the extinction of 90% of Earth’s species. Organisms that survived the mass extinction during the Permian period fall into three main categories. (1)the soft-bodied sponges, (2)cnidarians that include sea anemones, corals, and jellyfish, and (3)the annelids which are represented by segmented flatworms.  MESOZOIC ERA Mesozoic can be directly translated as "middle animals." The Mesozoic era has three major periods namely, the Triassic, Jurassic, and Cretaceous periods. However, the Mesozoic era also ended with another series of extinction events known as the "Great Extinction" that removed almost all species of big dinosaurs at the beginning of the Cenozoic era. Triassic period Pangaea was split into Laurasia and Gondwana (also called Gondwanaland), thus allowing the Atlantic Ocean to expand. The smaller continent, the Laurasia, eventually formed North America and Eurasia. On the other hand, Gondwana formed South America, Africa, Australia, Antarctica, and the Indian subcontinent. The environment of the Triassic period was generally warm. Dinosaurs evolved in the late-Triassic period along with crocodilians, flying reptiles, sea-reptiles, and mammals. Jurassic period A tectonic shift took place, several rifts were formed and filled with water, forming what would later become many of today's oceans and seas. Dinosaurs continued as the dominant species and evolved to be gigantic. Cretaceous period The climate remained similar to that of the Jurassic period, i.e., warm and humid. The environment evolved to the point that flowering plants (angiosperms) began to appear for the first time. It can be directly translated as "chalk" which is based on the abundance of chalk deposits during this time. This period also marked the end of the dinosaur age due to the “Great Extinction.” The direct cause of the massive extinction is still under debate, and many theories about this exist. The most dominant idea is the presence of large asteroids hitting Earth. CENOZOIC ERA Age of mammals It is divided into 3 periods: Paleogene, Neogene, and Quaternary. The Paleogene period is subdivided into three epochs: Paleocene, Eocene, Oligocene The Neogene is subdivided into two epochs: Miocene and Pliocene The Quaternary period has the Holocene and Pleistocene epochs. Paleogene period Paleocene epoch temporary warming trend, with - a temporary warming trend occurs causing the formation of thick forests that even reached the poles. thick forests eventually reaching - Mammals were heavily present during the Paleocene, but all of them were still quite small. the poles - The earliest primates, where the modern humans belong, appeared. extinction of non-avian dinosaurs Eocene period  - The Earth's condition was warm in the early Eocene, but changing ocean currents started worldwide cooling and drying. - Grasses had evolved forming grasslands that replaced forests. - Initially, the birds were the dominant animals, but they were eventually replaced by mammals as the dominant fauna. Oligocene period - The earth's environment continuously cools and becomes drier. The savannas and grasslands kept expanding. - Elephants started to appear. Neogene period Miocene epoch the climate became colder and - The climate is still cool and dry throughout this epoch. drier - The grazing mammals became increasingly important as a consequence of the grassland expansion. large and small mammals - The primates continuously diversified into different species which eventually led to the appearance of the flourished together with other human genera. phyla of organisms like insects Pliocene epoch and birds - The climate grew dryer and cooler. This drying process led to the desiccation of the Mediterranean Sea. - Also, deserts started to form in East Asia. - One of the most important organisms that appeared this time is the Australopithecines in African savannas, which is considered as a close human ancestor. Quaternary period Pleistocene epoch glaciation periods culminating to - Around at least four separate glaciation periods occurred during this ice age. the ice age - But Africa continued to become drier at this time causing the formation of African deserts, like Sahara and evolution of human genera Kalahari. - It is mainly characterized by the megafauna or very large mammals. However, these megafaunas were killed in a mass extinction that began toward the end of the Pleistocene. - The Pleistocene epoch is also a special time for the genus, Homo, where our species, Homo sapiens, evolved. - Human hunters contributed greatly to the extinction of megafauna near the end of the Pleistocene. Holocene epoch - Agriculture started in the Middle East. This is a great transition from hunting behavior to farming that affected the migration of early humans. - The writing system and the establishment of early civilization dated back to at least three thousand years ago in the Middle East. - Mass extinction of the Pleistocene megafauna continued until the early Holocene due to human activities. Reference: Quipper