History of Life on Earth (macroscopic level) - Lecture 2

• Paleontology is the scientific study of the existence of life, including the origin and extinction of different groups of organisms
• Paleontology incorporates disciplines such as biology, geology, ecology, archaeology, and computer science to study the evolution of organisms and their interaction with the environment
• Paleontologists specialize in studying the ecologies of the past and the evolution of organisms through careful observation and documentation of fossils
• Geology is the study of life on Earth based on evidence found in rocks
• Geologists study different materials that make up Earth to understand its history, focusing on changes over time in relation to climate and land formation
• The Geologic Timescale shows significant events in Earth's history and the evolution of living things, and scientists developed it by studying rock layers and index fossils worldwide
• Eons are the largest divisions in the Geologic Timescale, with the Phanerozoic, Proterozoic, Archaeozoic, and Hadean eons.
• The Phanerozoic eon began more than 500 million years ago and is characterized by organisms with skeletons and hard shells
• The Proterozoic eon is where the first multicellular organisms arose and mass extinction occurred
• The Archaeozoic eon is where the first life forms represented by single-celled organisms appeared
• The Hadean eon is characterized by Earth's formation from dust and gases
• Eras are smaller intervals within eons, with the Phanerozoic eon divided into Paleozoic, Mesozoic, and Cenozoic eras
• The Paleozoic era began about 540 million years ago and lasted for about 300 million years, rich in evidence of many marine organisms also known as the "Age of Marine Life"
• The Mesozoic era began about 200 million years ago and lasted for about 180 million years, known as the "Age of Dinosaurs" and sometimes "Age of Reptiles" because this is when many kinds of dinosaurs existed.
• The Cenozoic era is composed of the Quaternary and Tertiary

  periods, and is characterized by the presence of primitive mammals and modern human civilization, known as the "Age of Mammals"
• Periods are further subdivisions of eras, with the Proterozoic eon composed of the Vendian/Ediacaran period where prokaryotic organisms appeared; life formsfirst with the anaerobic life-forms, and then photosynthetic organisms. - life in this period only thrived underwater and few fossils existed because animals were all forms firstsoft bodied.
• The Paleozoic era is divided into periods such as the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian periods
• The Mesozoic era is 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 and their extinction could have been brought about by an asteroid impact and volcanism.
• The Cretaceous period ended with a meteorite-caused mass extinction
• The Tertiary period started the emergence of primitive mammals, while the Quaternary period is known as the "Age of Man" with the earliest modern humans believed to have existed
• Epochs are finer subdivisions shown in the Cenozoic era and parts of the Mesozoic era, done for the most recent portion of the geologic timescale
• The Geologic Timescale is an important tool to visually show Earth's history and identify organisms that existed in the past
• Paleontologists work to identify the forms of life that existed millions of years ago.
• Paleontologists figure out how things were in ancient times using fossil records.
• Geologists specifically investigate rock formations and even fossils to measure different physical properties of Earth.
• Geologists are scientists who carefully study different materials that make up Earth.
• Scientists obtained information from the pieces of evidence made it possible for them to identify the relative age of Earth.
• Scientists were also able to identify the different groups of organisms that have lived during a specific time group of groups of periods.
• The Proterozoic, Archaeozoic, and Hadean eons are sometimes collectively known as the Precambrian time, which accounts for almost 90% of Earth’s history.
• The Mesozoic era is also marked by the appearance of flowering plants.
• The Cenozoic era is considered to be the latest era in the geologic timeline, which began from 65 million years ago up to the present.
• Cambrian Period - organisms have hard body parts such as shells

  and outer skeletons (ex. jellyfish, worms, and sponges).
• Also common during the Cambrian period were the brachiopods, which were small animals with two shells and, Trilobites, the most dominant macroscopic life forms in this period.
• Ordovician and Silurian Periods are where the early forms of cephalopods (including octopi and squids)
• The first vertebrates, animals with backbones to appear in the Ordovician and Silurian period were jawless fishes that had suckerlike mouths. Invertebrates are animals without backbones, that first appeared in this period were insects.

  
  

  The first forms of land plants also appeared during these periods.
• Devonian Period is referred to as the “Age of Fishes” because many groups of fishes have evolved during this period. Most fishes had jaws, bony skeletons, and scales. Sharks appeared in the later parts of the period.
• The Carboniferous and Permian Periods is when reptiles, animals with scaly skin that lay eggs with tough leathery shells evolved from amphibians, and also winged insects evolved into many forms, such as dragonflies and cockroaches.
• At the end of the Paleozoic Era, many organisms became extinct, including trilobites and many amphibians.
• The mass extinction affected both plants and animals on land and even in the seas.
• As much as 95% of complex life forms in the oceans disappeared when the mass extinction occurred.