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

Early Earth 4 main stages in this process Abiotic synthesis of small organic molecules Monomers into polymers Protobionts 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 Inorganic molecules synthesized due to free energy and absence of oxygen Monomers served as building blocks for RNA and DNA

Extraterrestrial Sources of Organic Compounds Some of the organic compounds from which the first life on Earth arose May have come from space Carbonaceous chondrites (rocks, 1-2% carbon by mass) Fragments of a 4.5 billion-year-old collected in southern Australia in 1969 contained 80 a.a. similar to those produced by Miller-Urey experiments

The “RNA World” and the Dawn of Natural Selection The first genetic material Was probably RNA, not DNA DNA and RNA are carriers of genetic information through transcription, translation and replication Major features of the genetic code are shared by all modern living systems.

Complementary RNA copy Ribozymes 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 Figure 26.5 Ribozyme (RNA molecule) Template Nucleotides Complementary RNA copy 3 5

From RNA to DNA DNA Double stranded DNA is a much more stable repository for genetic information than the more fragile single stranded RNA Can be replicated more accurately After DNA appeared, RNA began to take on their modern roles as intermediates in translation of genetic programs How did RNA sequences come to carry the code for amino acid sequences?

Fossils: physical proof Fossils provide evidence for evolution Shows: rate of decay of isotopes, relationships with phylogenetic trees, and chemical properties or geographical data Dating fossils using Radiometric Dating technique Radioactive isotopes with longer half-lives are used to date older fossils (ex. Potassium -40 with a half life of about 1.3 billion years)

The fossil record chronicles a number of occasions 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 Millions of years ago 600 500 400 300 200 100 100 2,500 Number of taxonomic families 80 Permian mass extinction 2,000 Extinction rate 60 1,500 Extinction rate ( ) Number of families ( ) 40 1,000 Cretaceous mass extinction 20 500 Carboniferous Proterozoic eon Cambrian Ordovician Devonian Permian Cretaceous Silurian Paleogene Neogene Triassic Jurassic Figure 26.8 Paleozoic Mesozoic Ceno- zoic

Magnetic reversals of the north and south magnetic poles Magnetism of Rocks The magnetism of rocks Can also provide dating information Magnetic reversals of the north and south magnetic poles Have occurred repeatedly in the past Leave their record on rocks throughout the world

Seafloor Spreading

The oldest known fossils are stromatolites Prokaryotes Evolved The oldest known fossils are stromatolites Rocklike structures composed of many layers of bacteria and sediment Which date back 3.5 billion years ago First Prokaryotes were Earth’s sole inhabitants From 3.5 to about 2 billion years ago

Oxygenic photosynthesis Probably evolved about 3.5 billion years ago in cyanobacteria Figure 26.12

When oxygen began to accumulate in the atmosphere about 2 When oxygen began to accumulate in the atmosphere about 2.7 billion years ago It provided an opportunity to gain abundant energy from light It provided organisms an opportunity to exploit new ecosystems

Among the most fundamental questions in biology 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 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 Figure 26.13 Cytoplasm DNA Plasma membrane Ancestral prokaryote Infolding of plasma membrane Endoplasmic reticulum Nuclear envelope Nucleus Engulfing of aerobic heterotrophic Cell with nucleus and endomembrane system Mitochondrion eukaryote Plastid Engulfing of photosynthetic prokaryote in some cells Photosynthetic

In the process of becoming more interdependent The host and endosymbionts would have become a single organism The evidence supporting an endosymbiotic origin of mitochondria and plastids includes 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

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 Figure 26.15a, b 150 m 200 m (a) Two-cell stage (b) Later stage

The Colonial Connection The first multicellular organisms were colonies Collections of autonomously replicating cells 10 m Figure 26.16

The “Cambrian Explosion” Most of the major phyla of animals Appear suddenly in the fossil record that was laid down during the first 20 million years of the Cambrian period “explosion” included many large animals with hard shells and exoskeletons

Plants, fungi, and animals Molecular evidence Suggests that many animal phyla originated and began to diverge much earlier, between 1 billion and 700 million years ago Plants, fungi, and animals Colonized land about 500 million years ago

Often, these plates slide along the boundary of other plates Continental Drift Often, these plates slide along the boundary of other plates Pulling apart or pushing against each other Figure 26.18 North American Plate Caribbean Juan de Fuca Cocos Plate Pacific Nazca South African Scotia Plate Antarctic Arabian Eurasian Plate Philippine Indian Australian

Many important geological processes Occur at plate boundaries or at weak points in the plates themselves Volcanoes and volcanic islands Trench Oceanic ridge Oceanic crust Seafloor spreading Subduction zone Figure 26.19

The formation of the supercontinent Pangaea during the late Paleozoic era And its breakup during the Mesozoic era explain many biogeographic puzzles Figure 26.20 India collided with Eurasia just 10 million years ago, forming the Himalayas, the tallest and youngest of Earth’s major mountain ranges. The continents continue to drift. 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. Cenozoic North America Eurasia Africa South America India Madagascar Antarctica Australia Laurasia Mesozoic Gondwana At the end of the Paleozoic, all of Earth’s landmasses were joined in the supercontinent Pangaea. Pangaea Paleozoic 251 135 65.5 Millions of years ago

New information has revised our understanding of the tree of life Molecular Data Have provided new insights in recent decades regarding the deepest branches of the tree of life

Early classification systems had two kingdoms Plants and animals Five kingdom Figure 26.21 Plantae Fungi Animalia Protista Monera Eukaryotes Prokaryotes

Reconstructing the Tree of Life: A Work in Progress A three domain system Has replaced the five kingdom system Includes the domains Archaea, Bacteria, and Eukarya Each domain Has been split by taxonomists into many kingdoms