The History of Life on Earth Chapter 25 The History of Life on Earth

Past organisms were very different from those now alive Overview: Lost Worlds Past organisms were very different from those now alive The fossil record shows macroevolutionary changes over large time scales including The emergence of terrestrial vertebrates The origin of photosynthesis Long-term impacts of mass extinctions

Fig. 25-1 Figure 25.1 What does fossil evidence say about where these dinosaurs lived?

Fig 25-UN1 Cryolophosaurus

Concept 25.1: 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 (nonliving) synthesis of small organic molecules (e.g. aa & nitrogenous bases) 2. Joining of these small molecules into macromolecules (e.g. protein & nucleic acids) 3. Packaging of molecules into “protocells” (membranous droplets w distinct internal envir.) 4. Origin of self-replicating molecules (inheritance)

Synthesis of Organic Compounds on Early Earth Earth, along with the rest of the solar system, formed about 4.6 billion years ago. Earth’s early atmosphere likely contained: Water vapor, and Chemicals released by volcanic eruptions (nitrogen, nitrogen oxides, carbon dioxide, methane, ammonia, hydrogen, hydrogen sulfide)

Early Hypothesis (Reducing Atmosphere): A. I. Oparin & J. B. S. Haldane hypothesized: The early atmosphere was a reducing environment Stanley Miller & Harold Urey conducted lab experiments that showed: The abiotic synthesis of organic molecules in a reducing atmosphere is possible

However, the evidence is not yet convincing that the early atmosphere was in fact reducing Instead, the first organic compounds may have been synthesized: Near submerged volcanoes & deep-sea vents Amino acids have also been found in meteorites Small organic molecules polymerize when they are concentrated on hot sand, clay, or rock

Fig. 25-2 Figure 25.2 A window to early life?

Protocells Key properties of life: Replication, & Metabolism Aggregates of abiotically produced molecules Surrounded by a membrane or membrane- like structure Exhibit simple reproduction & metabolism Maintain an internal chemical environment

Experiments demonstrate that: Protocells could’ve 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

(a) Simple reproduction by liposomes Maltose (b) Simple metabolism Fig. 25-3 20 µm Glucose-phosphate Glucose-phosphate Phosphatase Starch Amylase Phosphate Maltose Figure 25.3 Laboratory versions of protobionts (a) Simple reproduction by liposomes Maltose (b) Simple metabolism

Self-Replicating RNA and the Dawn of Natural Selection The first genetic material: Was probably RNA, not DNA Ribozymes: RNA molecules Found to catalyze many different reactions For example, ribozymes can make complementary copies of: Short stretches of their own sequence, or Other short pieces of RNA

The fossil record documents the history of life The fossil record reveals changes in the history of life on earth Sedimentary rocks are deposited into layers called strata These strata are the richest source of fossils

Figure 25.4 Documenting the history of life Present Rhomaleosaurus victor, a plesiosaur Dimetrodon 100 million years ago Casts of ammonites 175 200 270 300 4.5 cm Hallucigenia 375 Coccosteus cuspidatus 400 1 cm Figure 25.4 Documenting the history of life Dickinsonia costata 500 525 2.5 cm 565 Stromatolites 600 Tappania, a unicellular eukaryote Fossilized stromatolite 3,500 1,500

Rhomaleosaurus victor, a plesiosaur Fig. 25-4b Figure 25.4 Documenting the history of life Rhomaleosaurus victor, a plesiosaur

Fig. 25-4c Figure 25.4 Documenting the history of life Dimetrodon

Casts of ammonites Fig. 25-4d Figure 25.4 Documenting the history of life Casts of ammonites

Coccosteus cuspidatus Fig. 25-4e Figure 25.4 Documenting the history of life 4.5 cm Coccosteus cuspidatus

Fig. 25-4f Figure 25.4 Documenting the history of life 1 cm Hallucigenia

2.5 cm Dickinsonia costata Fig. 25-4g Figure 25.4 Documenting the history of life Dickinsonia costata 2.5 cm

Tappania, a unicellular eukaryote Fig. 25-4h Figure 25.4 Documenting the history of life Tappania, a unicellular eukaryote

Fig. 25-4i Figure 25.4 Documenting the history of life Stromatolites

Fossilized stromatolite Fig. 25-4j Figure 25.4 Documenting the history of life Fossilized stromatolite

Animation: The Geologic Record Few individuals have fossilized, and even fewer have been discovered The fossil record is biased in favor of species that Existed for a long time Were abundant and widespread Had hard parts Animation: The Geologic Record

How Rocks and Fossils Are Dated Sedimentary strata reveal the relative ages of fossils Radiometric dating determines the absolute ages of fossils A “parent” isotope decays to: A “daughter” isotope at a constant rate The half-life of an isotope: Is the time required for half the parent isotope to decay Each isotope has a known half-life

1/2 1/4 1/8 1/16 Accumulating “daughter” isotope Fig. 25-5 Accumulating “daughter” isotope Fraction of parent isotope remaining 1/2 Remaining “parent” isotope 1/4 Figure 25.5 Radiometric dating 1/8 1/16 1 2 3 4 Time (half-lives)

Radiocarbon dating: Can be used to date fossils up to 75,000 years old For older fossils: Some isotopes can be used They date sedimentary rock layers above & below the fossil

Magnetism of rocks: Can provide dating information Reversals of the magnetic poles leave their record on rocks throughout the world

The Origin of New Groups of Organisms Tetrapods: The group of animals to which mammals belong Synapsids: Ancestor of mammals Evolution of unique mammalian features: Occurred through gradual modifications Can be traced from ancestral synapsids through the present

Synapsid (300 mya) Temporal fenestra Key Articular Quadrate Fig. 25-6-1 Synapsid (300 mya) Temporal fenestra Key Articular Quadrate Therapsid (280 mya) Dentary Squamosal Figure 25.6 The origin of mammals Temporal fenestra

Very late cynodont (195 mya) Fig. 25-6-2 Early cynodont (260 mya) Key Articular Temporal fenestra Quadrate Dentary Squamosal Later cynodont (220 mya) Figure 25.6 The origin of mammals Very late cynodont (195 mya)

Key events in life’s history (Geologic Record) The geologic record is divided into: The Archaean eon The Proterozoic eon: The archean & the proterozoic eons together lasted approximately 4 billion years

Key events in life’s history (Geologic Record), cont. The Phanerozoic eon: The last half billion years Encompasses most of the time that animals have existed on earth Encompasses multicellular eukaryotic life

Boundaries Between Geological Divisions Major boundaries between geological divisions: Correspond to extinction events in the fossil record

Ceno- zoic Meso- zoic Humans Paleozoic Colonization of land Animals Fig. 25-7 Ceno- zoic Meso- zoic Humans Paleozoic Colonization of land Animals Origin of solar system and Earth 1 4 Proterozoic Archaean Prokaryotes Figure 25.7 Clock analogy for some key events in Earth’s history Billions of years ago 2 3 Multicellular eukaryotes Single-celled eukaryotes Atmospheric oxygen

The First Single-Celled Organisms Stromatolites: The oldest known fossils Are, multilayered rock-like structures Composed of layers of bacteria & sediment Date back 3.5 billion years ago Prokaryotes were Earth’s sole inhabitants from 3.5 to about 2.1 billion years ago

Photosynthesis and the Oxygen Revolution Most atmospheric oxygen (O2): Is of biological origin Produced during photosynthesis (H2O-split step ) Photosynthesis O2: Is reacted with dissolved iron, and Precipitated to form banded iron formations The source of O2: Was likely bacteria similar to modern cyanobacteria

Fig. 25-8 Figure 25.8 Banded iron formations: evidence of oxygenic photosynthesis For the Discovery Video Early Life, go to Animation and Video Files.

By about 2.7 billion years ago, O2 began accumulating in: The atmosphere, and The rusting iron-rich terrestrial rocks This “oxygen revolution” from 2.7 to 2.2 billion years ago Posed a challenge for life Provided opportunity to gain energy from light Allowed organisms to exploit new ecosystems

The First Eukaryotes The oldest eukaryotic cell fossils: Date back 2.1 billion years An endosymbiont: Is a cell that lives within a host cell The endosymbiosis hypothesis: Proposes that mitochondria and plastids (chloroplasts and related organelles) were formerly small prokaryotes living within larger host cells

In the process of becoming interdependent: Prokaryotic ancestors of mitochondria & plastids probably gained entry to the host cell as: Undigested prey, or Internal parasites In the process of becoming interdependent: The host & endosymbionts became a single organism Serial endosymbiosis: Supposes that mitochondria evolved before plastids thru a sequence of endosymbiotic events

Break Slide Thur, Jan 23, ‘14

Endoplasmic reticulum Nucleus Fig. 25-9-4 Cytoplasm Plasma membrane DNA Ancestral prokaryote Endoplasmic reticulum Nucleus Nuclear envelope Aerobic heterotrophic prokaryote Photosynthetic prokaryote Mitochondrion Figure 25.9 A model of the origin of eukaryotes through serial endosymbiosis Mitochondrion Ancestral heterotrophic eukaryote Plastid Ancestral photosynthetic eukaryote

Key evidence supporting an endosymbiotic origin of mitochondria and plastids: Similarities of inner membrane structures & functions of these organelles to those of living prokaryotes Similar division “splitting” process of these organelles to that in some prokaryotes These organelles transcribe and translate their own DNA Their ribosomes are more similar to prokaryotic than eukaryotic ribosomes

The Origin of Multicellularity Evolution of eukaryotic cells allowed for: A greater range of unicellular forms A second wave of diversification resulted in: Evolvement of multicellularity giving rise to: Algae Plants Fungi Animals

The Earliest Multicellular Eukaryotes DNA sequence comparisons date the common ancestor of multi-cellular eukaryotes to: 1.5 billion years ago The oldest known fossils of multicellular eukaryotes are of small algae that lived about: 1.2 billion years ago

The “snowball Earth” hypothesis: Suggests that: Periods of extreme glaciation confined life to: the equatorial region, or deep-sea vents from 750 to 580 million years ago