Geological Time Scale, Fossils & Early Life

• History of life on Earth, including dates and sequence of the geologic time scale
• Characteristics of major groups of organisms present during these time periods

Background

• Earth formed along with the rest of the solar system 4.6 billion years ago
• Life on Earth arose around 3.5 billion years ago
• Both gradual and catastrophic processes have produced enormous changes over Earth's history

Protocells

• Term designating the first cells

Stromatolites

• They constitute the first fossil evidence of life
• Thought to have lived on earth 3.5 billion years ago
• They are layered sedimentary rocks formed by ancient cyanobacteria

Oxygen Revolution

• Occurred around 2 billion years ago
• Sudden increase in oxygen is due to the evolution of eukaryotic cells

Eukaryotic Organisms

• Fossil evidence shows that they are about 2.1 billion years old

Endosymbiotic Theory

• Provides an explanation on the origin of eukaryotes
• A prokaryote ingested some aerobic bacteria, and the aerobes were protected and produced energy for the prokaryote
• Over a long time the aerobes become mitochondria, no longer able to live on their own
• Some primitive prokaryotes also ingested cyanobacteria, which contain photosynthetic pigments
• The cyanobacteria become chloroplasts, no longer able to live on their own

Evidence Supporting Endosymbiotic Theory

• Prokaryotes show the same enzyme and transport systems as those of the mitochondria and plastids
• Present prokaryotes and the endosymbionts have similar ribosomal structures
• Endosymbionts contain a machinery that can transcribe and translate DNA into proteins similar to present prokaryotes
• Binary fission, as a mode of reproduction in prokaryotes, is similar to splitting mechanisms involved in reproduction of endosymbionts

Geological Time Scale

• Record that depicts Earth's history and the order of life from 2,500 million years ago to the present
• Scientists developed the time scale by studying fossils and layers of rock worldwide
• It spans Earth's entire history and is separated into four principal divisions

Paleontology

• This is the study of the history of life on Earth based on fossils

Fossils

• These are the remains of plants, animals, fungi, bacteria, and single-celled living things that have been replaced by rock material or impressions of organisms preserved in rock

Stratigraphy

• It's a scientific discipline concerned with the description of rock successions and their interpretation in terms of a general time scale
• It provides a basis for historical geology
• Its principles and methods have found application in such fields as petroleum geology and archaeology

Radioactive / Radiometric Dating

• This helped to determine the absolute divisions in the time scale
• It's a technique used to determine the age of materials such as rocks

Divisions of Geologic Times Scale

• Largest to Smallest: Eon, Era, Period, Epoch

Eon

• Largest segment of geologic time
• Spans hundreds to thousands of million of years ago

Hadean (4.5 – 4 billion years ago)

• Oldest eon and was officially recognized only in 2012
• Derived from the word Hades (God of the underworld in Greek mythology)
• Refers to hellish conditions and violent cosmic collisions that characterized Earth four billion years ago
• Represents Earth's earliest history, during which the planet was characterized by a partially molten surface, volcanism, and asteroid impacts
• Earth's continental and oceanic crust began to solidify

Archean (4,000 – 2,500 mya)

• Not much clear among geologists due to the few fossils or mineral evidence that could support it
• Began after the formation of Earth's crust, atmosphere, and seas
• Protocells evolved into anaerobic cells, and into prokaryotic archaea and bacteria

Proterozoic (2,500 – 541 mya)

• Characterized by the presence of oxygen in the atmosphere due to the emergence of cyanobacteria
• Cyanobacteria allowed other organisms, such as eukaryotes and other multicellular organisms to live
• Many anaerobic unicellular organisms disappeared because oxygen is toxic to them
• Prokaryotes with smaller prokaryotic symbionts evolved to become the first eukaryotic unicellular organisms which later gave rise to multicellular organisms
• During the Ediacaran Period (635 mya), multicellularity is evidenced by the fossil of diverse algae and soft-bodied invertebrates
• Grazers and suspension feeders or scavengers are called Ediacaran fauna that have given rise to cnidarians and bilaterians
• Dickinsonia costata – organism that lived during Ediacaran period

Phanerozoic (541 mya - present)

• Means "visible life"
• Divided into three major spans of time largely on the basis of characteristic assemblages of life-forms: Paleozoic, Mesozoic, Cenozoic ERAS

Era

• Span Time periods to tens to hundreds of millions of years

Pre-Cambrian

• Accounts for 88% of Earth's History
• The earliest living organisms were microscopic bacteria, which show up in the fossil record as early as 3.4 billion years ago
• Some three billion years ago the Earth's atmosphere was virtually devoid of oxygen
• It's thought the final stages of Precambrian time were marked by a prolonged global ice age

Paleozoic ERA (541 - 251 mya)

• The Cambrian period is the 1st Period of the Paleozoic Era
• Explosion of life in the oceans began during this era
• Most of the continents were covered in warm, shallow seas

Paleozoic Era (Ancient Life) Events:

• Invertebrates were dominate - Trilobites
• Fish emerged during this time
• Fish led to the arrival of amphibians
• The End of the Paleozoic Era is called the "Age of Amphibians"
• Early land plants including mosses, ferns and cone-bearing plants
• The early coal forming forests were also formed during this time
• At the end of the Paleozoic, the largest mass extinction in history wiped out approximately 90% of all marine animal species and 70% of land animals

Possible Causes of Mass Extinction Event:

• Lowering of sea levels when the continents were rejoined as Pangaea (convergent boundary)
• Increased volcanic activity (ash and dust)
• Climate changes – cooler climate

Cambrian Period (541 – 488 mya)

• Explosion of life
• All existing phyla come into being at this time
• Classes of marine animals with definite skeleton are present during this period
• Ediacaran animals – soft-bodied that leads to the appearance
• Marks the appearance of Marine invertebrates -trilobites and brachiopods, as well as echinoderms and arthropods
• The Cambrian Period is known as the "Age of the Trilobites"

Brachiopods

• Marine animals that resemble clams

Jawless (Agnathan) Vertebrates

• Organisms that emerged during the (541 – 488 mya) Cambrian Period
• Haikouichthys ercaicunensis - have notochord, gill pouches, eyes, segmented musculature, and other features similar to the present larval lampreys

Conodonts

• Possess teeth made of cellular bones

Ordovician Period (488 – 444 mya)

• Marked the appearance of the 1st animals with bones
• Dominant animals include trilobites, brachiopods and corals
• Marine animals are Epifaunal (live on the surface of the seafloor) or Infaunal (burrowing types)
• Also present were Sea stars and nautiloids – marine predators; and Agnathans (lack of jaw, being armored, and having no fins, survivors during this period, such as Hagfishes and lampreys)

Silurian Period (444 – 416 mya)

• Evolution of the jawed and finned marine vertebrates (gnathostomes)
• Groups of arthropods appeared: Chelicerates (spiders, scorpions) and Mandibulates (millipedes and centipedes)
• Wingless insects also appeared
• Small vascular plants (less than 10cm high) appeared with roots and vascular tissues like Cooksonia (a vascular plant in the Silurian period).
• Coral reefs expand and land plants begin to colonize barren land

Devonian (416 – 359 mya) - Age of the Fish

• Nautiloids gave rise to ammonoids (shelled cephalopods)
• Dominance in this period: fish
• Sarcopterygii are the Lobe-finned fishes (Lungfishes and rhipidistians (sacopterygians); Ichthyostegids - evolved from Sarcopterygii which become the first terrestrial tetrapod)
• Actinopterygii - ray-finned fishes that are ancestors of the modern teleosts.
• Plants become prominent by evolving from Chlorophyta (marine green alga), Mosses, Liverworts, and tracheophytes
• Land plants diversified and ferns, club mosses, horsetails, and large trees form
• Small plants sporandia develop (spore-bearing structure)

Carboniferous Period (359-299 mya)

• Warmer climate allowed the development of swamp forests populated by horsetails, clubmosses, and ferns
• Seeds protect the embryo from desiccation and to keep embryo nourished during development
• Anthracosaurs were classified as amphibian or reptile
• First wing insect evolved and diversified to dragonflies, orthopteroids, and hemipteroids

Permian Period (299-251 mya)

• This was the Last period of the Paleozoic
• Reptiles spread across continents
• Anthracosaurs gave rise to first amniotes (captorhinomorphs), Synapsids; and therapsids (mammal-like reptiles)
• Insects evolved to undergo complete metamorphosis including beetles, flies, caddisflies, and lepidopterans (moth and butterflies)
• Paleozoic Era (Ancient Life)
• Events at the end of the Paleozoic: Largest mass extinction in history
• Approximately 90% of all marine animal species and 70% of land animals were wiped out
• Possible causes of this Mass Extinction Event: Lowering of sea levels when the continents were rejoined as Pangaea (convergent boundary); Increased volcanic activity (ash and dust); and Climate changes – cooler climate

Mesozoic Era (Middle Life) (251-66 mya) Events:

• Pangaea broke up around the middle of this era
• Reptiles became the most abundant animals because of their ability to adapt to the drier climate of the Mesozoic Era
• Their skin maintains body fluids; and Embroyos live in shells
• The main plant life in the Mesozoic Era was Gymnosperms (plants that produce seeds, but no flowers, such as pine tress)
• Flowering plants appeared at the END of this 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.

Mesozoic Mass Extinction

• Asteroid or Comet collides with Earth
• Huge cloud of smoke and dust fills the air, blocks out sunlight, and causes Plants/Animals that eat plants/Animals that eat plant-eaters to die
• Many animals you see today are descendants from the survivors of this extinction event

Triassic Period (251-199.6 mya)

• First dinosaurs appear
• Mammals first appear as small rodents
• The fauna and life re-diverisfy
• The first turtle fossil comes from this period
• Foraminiferans, modern corals, and bony fishes evolved
• Mollusk developed thick shells and spines
• Ichthyosaurus - marine reptiles with dolphinlike appearance gave birth to live young
• Two groups of diapsids evolved: Lepidosauromorphs (related to lizard) & Archosauromorphs (predators)
• Pterosaurs developed that were capable of powerful flight urther diversified into large flying vertebrates and small sparrows.
• Saurischia developed including carnivores, bipedal theropods, herbivores, and quadrupedal sauropods & also included Tyrannosaurus rex and Deinonychus (theropods) & Apatosaurus (herbivores sauropods; with a small head and long neck, for example, Brontosaurus/Brachiosaurus/Diplodocus

Jurassic Period (201.3 – 145 mya)

• Dinosaurs flourish, this is deemed the “Golden age of dinosaurs”
• First birds appear
• Gymnosperms develop, such as cycads and conifers, including Ginkgo and giant ferns

Cretaceous Period (145 – 66 mya)

• T-Rex emerges
• First snakes and primates appear
• Deciduous trees and grasses commoned developed
• First flowering plants evolved
• Mass extinction (K/T (Creataceous-Tertiary) extinction) marks the end of the Mesozoic Era with the demise of dinosaurs
• The extinction also lead to the loss of 25% of all marine life

Cenozoic Era – Recent Life (66 mya - present)

• Began about 65 million years ago and continues today
• Climate was warm and mild
• Marine animals such as whales and dolphins evolved
• Mammals began to evolve to live in land, air, and sea
• Grasses provided a food source for grazing animals
• Many mountain ranges formed during the Cenozoic Era
• Alps in Europe and Himalayas in India; Rocky Mountains in the USA

Cenozoic Era Features

• Growth of mountains cooled down climate and ice ages occurred late during the Cenozoic Era (Quaternary Period)
• As the climate changed, the oceans rose and fell caused by melting glaciers
• Cenozoic Era: also considered the "Age of Mammals", is comprised of marine organisms like Algae/Mollusks/Fish and Mammals
• Land Animals present include Bats/Cats/Dogs/Cattle and Humans (thought to have appeared during 3.5 million years ago-Quaternary)
• Flowering plants were now most prevalant.
• EPOCH - Smallest segment of geologic time characterized by distinctive organisms
• First horses appear and tropical plants dominate during the (Paleocene), Grasses spread and whales, rhinos, elephants and other large mammals develop & Sea level rises and limestone deposits form occurred in the (Eocene) Epoch; Dogs, cats, and apes develop(Oligocene), Horses, mastadons, camels, and tigers freely developed (Miocene); Hominids and the Grand Canyon formed (Pliocene); modern humans devoloped, ice sheets, ice age (Pleistocene); Holocene Humans prospered (Holocene).

Explore fossils, stratigraphy, radiometric dating, and geological time. Understand Earth's eons, Hadean conditions, stromatolites, and endosymbiotic theory. Examine the oxygen revolution, protocells, and the differences between prokaryotic and eukaryotic cells.