bio_4_history

• The Earth is about 4.6 billion years old (time of the first likely solid surface)
• Evidence for the age of the Earth

  • Radioisotope dating of oldest known Earth minerals (4.4 billion years ago)
  • Radioisotope dating of oldest known rocks on Earth (4.1 billion years ago)
  • Radioisotope dating of oldest known meteorites (4.6 billion years ago; for the age of the solar system)
• Earth's early atmosphere (when life first appears in the fossil record) most likely consisted of CO2, H2O, CO, H2, N2, and small amounts of NH3, H2S, and CH4
• The early Earth had little or no free oxygen
• The early Earth had abundant energy sources such as volcanism, thunderstorms, and bombardment with particles and radiation from space, especially important is more UV radiation than today
• The four requirements for the current model for chemical evolution of life were likely met in the early Earth: little or no free oxygen, abundant energy sources, chemical building blocks of water, dissolved mineral ions, and atmospheric gases, and plenty of time before the first traces of life from 3.8 billion years ago
• Spontaneous Generation (Abiogenesis)


  The hypothesis that life arises regularly from non-living things
• Scientists that helped to disprove Spontaneous Generation (Abiogenesis)

  • Francesco Redi (1668) - demonstrated that maggots were the offspring of flies, not products of spontaneous generation
  • Louis Pasteur (1859) - Microorganisms do not arise from meat broth

  
• The Miller/Urey Experiment (1953)


  Simulated the conditions of Earth's early atmosphere and oceans, adding energy to simulate the lightning that was believed to be common place. After one week, 10-15% of the carbon had turned into organic compounds, and 2% of the carbon had created amino acids, the building blocks of proteins/life.
• Primordial Soup Hypothesis


  Alexander Ivanovich Oparin (1920s) proposed that the atmosphere of early Earth was very reactive, with numerous incidents of lightning and high levels of ultraviolet radiation. He also claimed that life on Earth developed through gradual chemical changes of organic molecules, in the "primordial soup" which likely existed on Earth four billion years ago.

  
• Exogenesis


  The hypothesis that life on Earth was seeded from an extraterrestrial source, and that primitive life may have originally formed extraterrestrially either in space or nearby planet such as Mars.
• Protobionts


  The simple cell that is the precursor to life. They resemble very simple cells and are microspheres composed of inorganic and organic molecules trapped inside of a lipid bilayer membrane.
• RNA world hypothesis


  RNA can catalyze a variety of reactions, including some self-catalytic reactions. RNA can also store genetic information. In vitro evolution of RNA has shown that the RNA world hypothesis is feasible - selection can act on self-replicating RNA molecules in vitro. DNA likely came later and had the selective advantage of greater stability.
• The first evidence of life in the fossil record are isotopic carbon "fingerprints" in rocks from ~3.8 billion years ago
• The first evidence of cells are microfossils of prokaryotic cells in fossils of stromatolites dated to ~3.5 billion years ago
• Stromatolites


  Rocklike structures made up of layers of bacteria and sediment. In some areas stromatolites are still being formed today.
• The first cells were most likely anaerobic heterotrophs, as there was likely an abundance of organic molecules available for food early on. Later, as organic molecules became scarcer, photosynthetic organisms were favored.
• The first photosynthetic organisms were likely the purple and green sulfur bacteria, which use H2S as a hydrogen donor.
• Microfossils


  The oldest ones found on Earth date to ~3.5 billion years ago.
• Banded iron formations from about 2.5 billion years ago indicate the massive release of O2 into the oceans.
• By 2 billion years ago, O2 levels began to build up in the atmosphere. The presence of O2 had a profound impact on life on Earth - it is toxic to organisms that don't have protective mechanisms, many died as O2 levels built up, it creates an oxidizing atmosphere which can destroy precious reduced organic molecules, some anaerobic organisms survive only in environments with little to no oxygen, some evolved adaptations to the presence of oxygen, and some organisms developed means to use O2 in respiration to extract more energy from foods (aerobic respiration).
• The formation of the ozone layer (O3) soon after oxygenation of the atmosphere provided protection from UV radiation and allowed life to expand to regions at and near the Earth's surface.
• Eukaryotic cells first appear in the fossil record about 2 billion years ago, long after prokaryotic cells.
• DNA sequencing provides evidence of common ancestry of all life on Earth, with eukaryotes splitting from Archaea about 2 billion years ago.
• Paleontology


  The scientific study of the existence of life; including the origin and eventual destruction or extinction of different groups of organisms, through careful observation and documentation of fossils.
• Paleontologists


  Scientists who specialize in studying the ecologies of the past and the evolution of organisms that thrived in these ecologies through careful observation and documentation of fossils. They work to identify the forms of life that existed millions of years ago.
• Geology


  The study of life on Earth based on the evidence found on rocks.
• Geologists


  Scientists who carefully study the different materials that make up Earth. They work to understand the history of Earth by focusing on the changes of Earth over time in relation to changes in Climate and land formation. They specifically investigate rock formations and even fossils to measure different physical properties of Earth.
• Paleontologists look at the fossil remains of different types of organisms beneath the surface of Earth to study primitive life, while geologists study the outer layer of Earth's crust to understand the history of Earth. Both work together to understand the history or evolution of life on Earth and use the geologic time scale to divide Earth's history into time intervals.
• Geologic Time Scale


  A scientific tool used to represent evolutionary time, showing significant events in the history of Earth and of the evolution of living things, developed by studying rock layers and index fossils worldwide. It is divided into several levels: eons, eras, periods, and epochs.
• Eons in the Geologic Time Scale

  • Hadean Eon
  • Archaeozoic Eon
  • Proterozoic Eon
  • Phanerozoic Eon
• Hadean Eon


  From 4.6 to 3.9 billion years ago, characterized by Earth's formation from dust and gases.
• Archaeozoic Eon


  From 3.9 to 2.5 billion years ago, where the first life-forms represented by single-celled organisms appeared.
• Proterozoic Eon


  From 2.5 billion years ago to 540 million years ago, where the first multicellular organisms arose and mass extinction occurred.
• Phanerozoic Eon


  The recent eon which began more than 500 million years ago, with the existence of organisms that had skeletons or hard shells.
• Eras in the Geologic Time Scale

  • Pre-Cambrian Era
  • Paleozoic Era
  • Mesozoic Era
  • Cenozoic Era
• Pre-Cambrian Era


  Accounts for almost 88% of Earth's history.
• Paleozoic Era


  Began about 540 million years ago and lasted for about 300 million years. Many kinds of organisms lived during this era, and fossil records became rich with evidence of many marine organisms. Pangea was starting to form.
• Mesozoic Era


  Began about 200 million years ago and lasted for about 180 million years. Also called the Age of Dinosaurs and the Age of Reptiles. Also marked by the appearance of flowering plants.
• Cenozoic Era


  The latest era in the geologic timeline, began from 65 million years ago up to the present. Mammals have evolved and adapted to live in various environments, including land, water, and even air. Sometimes called the Age of Mammals.