The Tree of Life: An Introduction to Biological Diversity Chapter 26

Overview: Changing Life on a Changing Earth Life is a continuum extending from the earliest organisms to the variety of species that exist today Geological events change the course of evolution Conversely, life changes the planet that it inhabits

Planet Formation

Planet Formation http://www.fas.org/irp/imint/docs/rst/Sect20/planet_quickly_021128_02,0.jpg

Planet Formation http://cougar.jpl.nasa.gov/HR4796/anim.html

Conditions on early Earth made the origin of life possible Chemical and physical processes on early Earth may have produced very simple cells through a sequence of stages: 1. Abiotic synthesis of small organic molecules 2. Joining of these small molecules into polymers 3. Packaging of molecules into “protobionts” 4. Origin of self-replicating molecules

Synthesis of Organic Compounds on Early Earth Earth formed about 4.6 billion years ago, along with the rest of the solar system Earth’s early atmosphere contained water vapor and chemicals released by volcanic eruptions

Synthesis of Organic Compounds on Early Earth Ancient Atmospheric Gases—H2O, CH4 (methane), NH2 (ammonia) Additional gases (common emissions of modern volcanoes)—CO, CO2, N2, H2O vapor, H2S/FeS, HCN, H2 Meteor bombardment Lightning, heat, and UV radiation served as energy sources

Experiments simulating an early Earth atmosphere produced organic molecules from inorganic precursors, but such an atmosphere on early Earth is unlikely LE 26-2 Water vapor CH4 NH3 H2 Electrode Condenser Cold water Cooled water containing organic molecules Sample for chemical analysis H2O Stanley Miller

Instead of forming in the atmosphere, the first organic compounds may have been synthesized near submerged volcanoes and deep-sea vents www.pmel.noaa.gov/vents/geology/video_other.html http://www.ocean.udel.edu/kiosk/bsmoker.html

Extraterrestrial Sources of Organic Compounds Some organic compounds from which the first life on Earth arose may have come from space Carbon compounds have been found in some meteorites that landed on Earth Some carbonaceous chondrites have revealed the presence of 74 different amino acids, and all 5 of the cross-linking bases of RNA and DNA.

Mars Rock and putative microbes

Abiotic Synthesis of Polymers Small organic molecules polymerize when they are concentrated on hot sand, clay, or rock Electrical charges concentrate monomers; dehydration reactions create polymers Sydney Fox demonstrated formation of proteinoids (abiotically synthesized polypeptides) http://www.darwinismrefuted.com/molecular_biology_13.html

Protobionts Protobionts are aggregates of abiotically produced molecules surrounded by a membrane or membrane-like structure Experiments demonstrate that protobionts could have formed spontaneously from abiotically produced organic compounds For example, small membrane-bounded droplets called liposomes can form when lipids or other organic molecules are added to water

Liposome Glucose-phosphate Phosphorylase Amylase Starch Maltose LE 26-4 Glucose-phosphate Phosphorylase Amylase Starch Maltose Phosphate Simple metabolism Simple reproduction 20 mm Liposome

Protobionts Microspheres—made from proteinoids mixed in cool water Liposomes—spheres made of phospholipids mixed with water (similar to phospholipid bilayer) Coacervates—colloidal drops of polypeptides, nucleic acids, and polysaccharides Microspheres Liposomes

The “RNA World” and the Dawn of Natural Selection The first genetic material was probably RNA, not DNA RNA molecules called ribozymes have been found to catalyze many different reactions, including: Self-splicing Making complementary copies of short stretches of their own sequence or other short pieces of RNA

Ribozyme (RNA molecule) 3¢ Template 3¢ Nucleotides Complementary RNA copy 5¢ 5¢ Early protobionts with self-replicating, catalytic RNA would have been more effective at using resources and would have increased in number through natural selection

First Genetic Material and Enzymes may both have been RNA

The fossil record chronicles life on Earth Fossil study opens a window into the evolution of life over billions of years www.dickinson.edu/~nicholsa/Romnat/fossils.htm

How Rocks and Fossils Are Dated Sedimentary strata reveal the relative ages of fossils http://www.gly.fsu.edu/~salters/GLY1000/12Rock_record_time/Slide12.jpg

Grand Canyon www.euxus.de/usa-page-grand-canyon.html

Index fossils are similar fossils found in the same strata in different locations They allow strata at one location to be correlated with strata at another location

Determining Age of Fossils Relative age—placement in strata layers Absolute age—determined by radiometric dating The magnetism of rocks can provide dating information Magnetic reversals of the magnetic poles leave their record on rocks throughout the world

Ratio of parent isotope LE 26-7 Accumulating “daughter” isotope Ratio of parent isotope to daughter isotope 1 2 Remaining “parent” isotope 1 4 1 8 1 16 1 2 3 4 Time (half-lives)

The Geologic Record By studying rocks and fossils at many different sites, geologists have established a geologic record of Earth’s history scamp.wr.usgs.gov/scamp/html/scg_time.html

The geologic record is divided into three eons: the Archaean, the Proterozoic, and the Phanerozoic The Phanerozoic eon is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic Each era is a distinct age in the history of Earth and its life, with boundaries marked by mass extinctions seen in the fossil record Lesser extinctions mark boundaries of many periods within each era

Mass Extinctions The fossil record chronicles a number of occasions when global environmental changes were so rapid and disruptive that a majority of species were swept away Mass extinctions provided life with unparalleled opportunities for adaptive radiations into newly vacated ecological niches www.jkaneart.com/massextinctiongraph.htm

LE 26-8 Millions of years ago 600 500 400 300 200 100 Permian mass extinction 80 60 40 20 Extinction rate Cretaceous mass extinction 2,500 2,000 1,500 1,000 Neogene Proterozoic eon Cambrian Ordovician Silurian Devonian Carboniferous Permian Triassic Jurassic Paleogene Paleozoic Mesozoic Ceno- zoic Number of families ( ) Extinction rate ( Number of taxonomic families

It may have been caused by volcanic eruptions The Permian extinction killed about 96% of marine animal species and 8 out of 27 orders of insects It may have been caused by volcanic eruptions The Cretaceous extinction doomed many marine and terrestrial organisms, notably the dinosaurs It may have been caused by a large meteor impact NORTH AMERICA Chicxulub crater Yucatán Peninsula

As prokaryotes evolved, they exploited and changed young Earth The oldest known fossils are stromatolites, rocklike structures composed of many layers of bacteria and sediment Stromatolites date back 3.5 billion years ago

Modern stromatolites in Shark Bay, Australia Mats of photosynthetic organisms – cyanobacteria, algae and phototrophs

The First Prokaryotes Prokaryotes were Earth’s sole inhabitants from 3.5 to about 2 billion years ago Electron transport systems were essential to early life The earliest types of photosynthesis did not produce oxygen Oxygenic photosynthesis probably evolved about 3.5 billion years ago in cyanobacteria

Effects of oxygen accumulation in the atmosphere about 2 Effects of oxygen accumulation in the atmosphere about 2.7 billion years ago: Posed a challenge for life Provided opportunity to gain energy from light Allowed organisms to exploit new ecosystems

Eukaryotic cells arose from symbioses and genetic exchanges between prokaryotes Among the most fundamental questions in biology is how complex eukaryotic cells evolved from much simpler prokaryotic cells The oldest fossils of eukaryotic cells date back 2.1 billion years

Endosymbiotic Origin of Mitochondria and Plastids The theory of endosymbiosis proposes that mitochondria and plastids were formerly small prokaryotes living within larger host cells The prokaryotic ancestors of mitochondria and plastids probably gained entry to the host cell as undigested prey or internal parasites In the process of becoming more interdependent, the host and endosymbionts would have become a single organism

Key evidence supporting an endosymbiotic origin of mitochondria and plastids: Similarities in inner membrane structures and functions Both have their own circular DNA

Multicellularity evolved several times in eukaryotes After the first eukaryotes evolved, a great range of unicellular forms evolved Multicellular forms evolved also Molecular clocks date the common ancestor of multicellular eukaryotes to 1.5 billion years The oldest known fossils of eukaryotes are of relatively small algae that lived about 1.2 billion years ago

Larger organisms do not appear in the fossil record until several hundred million years later Chinese paleontologists recently described 570-million-year-old fossils that are probably animal embryos 150 mm 200 mm Two-celled stage of embryonic development (SEM) Later embryonic stage (SEM)

The Colonial Connection The first multicellular organisms were colonies, collections of autonomously replicating cells Some cells in the colonies became specialized for different functions The first cellular specializations had already appeared in the prokaryotic world

The “Cambrian Explosion” Most of the major phyla of animals appear in the fossil record of the first 20 million years of the Cambrian period Two animal phyla, Cnidaria and Porifera, are somewhat older, dating from the late Proterozoic Cnidaria Porifera

Molecular evidence suggests that many animal phyla originated and began to diverge much earlier, between 1 billion and 700 million years ago

Colonization of Land by Plants, Fungi, and Animals Plants, fungi, and animals colonized land about 500 million years ago Symbiotic relationships between plants and fungi are common today and date from this time www.fcps.edu/.../mpages/common_greenshield.htm

Colonization of Land by Plants, Fungi, and Animals With the development of photosynthetic bacteria came the development of an atmosphere containing oxygen UV radiation from the sun reacted with the oxygen to form the ozone layer around the earth Protected organisms from destructive radiation, allowing them to survive on the land

Arthropods ~100 million years after plants/fungi covered the earth, animals could survive on land Arthropods are believed to be the first Have hard outer skeleton and jointed limbs Lobsters, insects, crabs, spiders Specific traits allowed certain animals to survive and reproduce and pass on their genes Eryon arctiformis

Vertebrates Animals with backbones (endoskeletons) The first were jawless fishes (500 mya) 430 mya jawed fishes

Vertebrates Amphibians –first vertebrates on land Had lungs, allowing them to absorb oxygen from the air Limbs believed to be derived from bones if fish fins Strong, flexible internal skeleton allowed animals to be much larger than insects Plethodon glutinosus: Slimy Salamander Lysorophid amphibian

Vertebrates Reptiles –350 mya Watertight skin protected from dessication Lay eggs with shells on land Better adapted to dry climate Iguana

Vertebrates Birds Winged animals Can fly Hollow skeleton

Evolution of Organisms Extinctions –death of a species opens up niches for other species to become more abundant Continental drift—movement of Earth’s land masses over geologic time Contributed to geographic distribution of some species Marsupials in Australia and South America

Continental Drift The continents drift across our planet’s surface on great plates of crust that float on the hot underlying mantle These plates often slide along the boundary of other plates, pulling apart or pushing each other

Eurasian Plate North American Plate Philippine Caribbean Juan de Fuca LE 26-18 North American Plate Eurasian Plate Philippine Indian Arabian Australian Antarctic African Scotia Plate South Nazca Pacific Cocos Plate Juan de Fuca Caribbean

Many important geological processes occur at plate boundaries or at weak points in the plates Volcanoes and volcanic islands Trench Oceanic ridge Oceanic crust Subduction zone Seafloor spreading

LE 26-20 By about 10 million years ago, Earth’s youngest major mountain range, the Himalayas, formed as a result of India’s collision with Eurasia during the Cenozoic. The continents continue to drift today. By the end of the Mesozoic, Laurasia and Gondwana separated into the present-day continents. By the mid-Mesozoic Pangaea split into northern (Laurasia) and southern (Gondwana) landmasses. At the end of the Paleozoic, all of Earth’s landmasses were joined in the supercontinent Pangaea. 65.5 135 251 Millions of years ago Cenozoic Mesozoic Paleozoic North America Eurasia Africa India South America Madagascar Australia Antarctica Laurasia Gondwana Pangaea The formation of the supercontinent Pangaea during the late Paleozoic era and its breakup during the Mesozoic era explain many biogeographic puzzles

New information has revised our understanding of the tree of life Molecular data have provided insights into the deepest branches of the tree of life

Previous Taxonomic Systems Plantae Fungi Animalia Protista Monera Eukaryotes Prokaryotes Early classification systems had two kingdoms: plants and animals Robert Whittaker proposed five kingdoms: Monera, Protista, Plantae, Fungi, and Animalia

Reconstructing the Tree of Life: A Work in Progress The five kingdom system has been replaced by three domains: Archaea, Bacteria, and Eukarya Each domain has been split into kingdoms serc.carleton.edu/.../creationism/mechevol.html www.windows.ucar.edu/.../tour_evolution_1.html