The Earth is 4.6 billion years old! Earth History Mrs. Burkey ESS Cy Creek HS 17-18 If the Earth formed at midnight 6:00 am First life appears 10:00 pm First animals/plants on land 11:59 pm First humans evolve What is the Earth s time scale? The Geological time scale is a record of the life forms and geological events in Earth s history. Scientists developed the time scale by fossils world wide. Radioactive dating (like Carbon Dating) helped determine the absolute divisions in the time scale. Geological time Scale (largest to smallest) Super-eon Eon Era* - 4 Period* -11 Epoch - Current Age - Current FOUR Eras PRE-CAMBRIAN 88% of earth s history Paleozoic (ancient life) 544 million years ago lasted 300 million yrs Mesozoic (middle life) 245 million years ago lasted 180 million yrs Pre-Cambrian Began with the formation of the Earth 4.6 billion years ago. Accounts for 88% of whole Earth History. Simple bacteria only. Cenozoic (recent life) 65 million years ago continues through present day 1
Paleozoic Era Ancient Life Explosion of life in the oceans began during this era. Most of the continents were covered in warm, shallow seas. Invertebrates were dominate Fish emerged which led to the arrival of amphibians The early coal forming forests were also formed during this time. Carboniferous Period Paleozoic Era Divided into 5 periods: Cambrian period - Age of the Trilobites Ordovician period - First fishes evolved and other species become extinct Silurian period - Land plants, insects and spiders appear Devonian period - Amphibians evolve and cone-bearing plants start to appear. Carboniferous period - Tropical forests appear and reptiles evolve. Where we get most of our coal/fossil fuel now. Permian period - Seed plants become common and insects and reptiles become widespread. Mesozoic Era middle life Dinosaurs were also very active in this era. First small dinosaurs appeared in the Triassic Period. Larger and more abundant dinosaurs appeared in the Jurassic Period. Small mammals and birds also appeared during this era. Mesozoic Era Divided into 3 periods: Triassic period - Turtles and crocodiles evolve and dinosaurs appear. Jurassic period - Large dinosaurs roam the world. First mammals and birds appear. Cretaceous period - Flowering plants appear, mammals become more common, dinosaurs become extinct. 2
Mesozoic Mammals Mesozoic Reptiles End of the Mesozoic Era This era ended with a mass extinction event about 65 million years ago. Many groups of animals, including the dinosaurs disappeared suddenly at this time. Many scientists believe that this event was caused by a comet or asteroid colliding with the Earth. Cenozoic Era Recent Life Began about 65 million years ago and continues today!!!!! Climate was warm and mild. Marine animals evolved. Mammals began to increase and evolve adaptations that allowed them to live in many different environments land, air and the sea. This era is sometimes called the Age of Mammals Cenozoic Era Divided into 2 periods: Tertiary period - First primates appear and flowering plants become the most common. Quaternary period - Humans evolve and large mammals like woolly mammoths become extinct. 3
Mass Extinctions Source: http://dsc.discovery.com/earth/wide-angle/massextinctions-timeline.html #37-40, #6 Mass extinctions are NOT unusual 99% of all things that have ever lived, have gone extinct There have been 5-6 major mass extinction events Causes of Mass Extinctions #37 1. Asteroid or comet impacts 2. Climate changes 3. Volcanic eruptions 4. Sea level changes 5. Oxygen in the atmosphere Asteroid or Comet Impacts Dust kicked up may block out the Sun for years Perennial winter Global wildfires from molten impact debris Climate Changes Shifts in climates can eliminate or move entire habitats. Plate Tectonics Alters major circulation patterns Volcanic eruptions Living organisms can alter atmospheric gas concentrations and global thermostat 4
Volcanic Eruptions Some last hundreds or thousands of years Areas covered by vast deposits of lava (flood basalts, traps) Change global climate by releasing large amounts of carbon dioxide into atmosphere Sea Level Changes Affects mostly shallow coastal areas Caused by climate change (melting/freezing of ice caps and glaciers) and tectonic activity Oxygen in the Atmosphere Highly variable, current level is 21% Unicellular photosynthetic organisms added oxygen for 2 billion years (600 mya ~15%) Explosion of multicellular life 2.5-2.2 bya (Precambrian era) Almost all anaerobes Oxygen Holocaust Evolution of photosynthetic organisms added oxygen to the atmosphere killing most anaerobic organisms 445 mya (Late Ordovician period) 57% extinction Most organisms lived in the sea at this time Causes Sea level drop caused by plate tectonics Pangea over south pole at this time large glacier 370 mya (Late Devonian period) 50% extinction Causes Fluctuating sea levels Land plants removed CO 2 from atmosphere (global cooling) More glaciers 5
250 mya #38, 40 (End of Permian period) 200 mya (end of Triassic period) 83% extinction The Great Dying event 96% of all marine species 70% of all land vertebrates Arthropods Land plants Likely causes Eruption of Siberian Traps Formation of Pangaea disrupted ocean currents Possible meteor impact 48% extinction Large marine extinction Ammonites Corals Seed ferns Likely caused by eruption of the Central Atlantic province Sulfur gas blocked Sun Large amount of lava released over several centuries K-T Boundary ~65 mya T How could volcanic eruptions lead to sea level changes? #39 50% extinction Asteroid impact Break up of Pangaea Eruption of Deccan Traps in India Marks the end of the Cretaceous period, Mesozoic era End of the age of reptiles / dinosaurs K Ash SO 2 gas Ash blocks out sun Gases (SO 2, CO 2 ) add to global warmin g Temp, glacier s form Temp, glacier s melt Sea level drops Sea level rises Principle of Faunal Succession Fossils in rocks occur in a fixed sequence worldwide. Index Fossil abundant, widespread, and lived for a short span of geologic time These fossils can be used to correlate and relatively date rocks in which they are found. Which would make the best index fossil? 6
Absolute Age Absolute Age the numeric age of an object, or event, often stated in years before the present. Ways to Determine Absolute Age 1. Rates of Erosion 2. Rates of Deposition 3. Varve Count 4. Radioactive Dating #23 1. Rates of Erosion By measuring how fast a river erodes, geologists can estimate how old it must be. Only accurate for 10,000 20,000 years old. Niagara Falls erodes at the rate of 1.3 meters per year Erosion of Niagara Falls 2. Rates of Deposition Geologists estimate that it takes about 1,000 years to deposit 30 centimeters of sedimentary rock. This is not a highly accurate way of measuring age but can give useful estimates. 7
3. Varve Count Varves are sedimentary rock layers that occur annually. Ice core section showing annual layers. Caused by glaciers freezing and thawing. Just like tree rings! (Dendrochronology) 4. Radioactive dating: Half life #24 Start 1 2 3 4 0 half-life half-life half-life half-life 100% 50% 25% 12.5% 6.25% the amount of time needed for half the parent isotope to decay to daughter isotope Does Not Change- intensive property How to calculate Half-lives Find % of parent material remaining # of half-lives completed Determine amount of time that has past Example: Find % of parent material remaining # of halflives completed Determine amount of time that has past The half-life of radon-222 is 3.8 days. How much of a 100g sample is left after 15.2 days? 8