NOTES: CH 25 - The History of Life on Earth

History of Life Eras Boundaries between units in the Geologic Time Scale are marked by dramatic biotic change A figure from Ch. 26… 4500 Origin of Earth

Overview: Lost Worlds ● Past organisms were very different from those now alive ● The fossil record shows macroevolutionary changes over large time scales, for example: The emergence of terrestrial vertebrates The impact of mass extinctions The origin of flight in birds

Prebiotic Chemical Evolution: ● Earth’s ancient environment was different from today: -very little atmospheric oxygen -lightning, volcanic activity, meteorite, bombardment, UV radiation were all more intense

● Chemical evolution may have occurred in four stages: 1) abiotic synthesis of monomers 2) joining of monomers into polymers (e.g. proteins, nucleic acids) 3) formation of protocells (droplets formed from clusters of molecules) 4) origin of self-replicating molecules that eventually made inheritance possible (likely that RNA was first)

Oparin / Haldane hypothesis (1920s): the reducing atmosphere and greater UV radiation on primitive Earth favored reactions that built complex organic molecules from simple monomers as building blocks

Miller / Urey experiment: Simulated conditions on early Earth by constructing an apparatus containing H2O, H2, CH4, and NH3. Results: ● They produced amino acids and other organic molecules. ● Additional follow-up experiments have produced all 20 amino acids, ATP, some sugars, lipids and purine and pyrimidine bases of RNA and DNA.

Mass of amino acids (mg) 20 200 Number of amino acids Mass of amino acids (mg) Figure 25.2 Amino acid synthesis in a simulated volcanic eruption. 10 100 1953 2008 1953 2008

● Protocells: collections of abiotically produced molecules able to maintain an internal environment different from their surroundings and exhibiting some life properties such as metabolism, semipermeable membranes, and excitability (experimental evidence suggests spontaneous formation of protocells)

Abiotic genetic replication

possible formation of protocells; self-repliating RNA as early “genes”

Origin of Life - Different Theories:   *Experiments indicate key steps that could have occurred. ● Panspermia: some organic compounds may have reached Earth by way of meteorites and comets meteorite

● Sea floor / Deep-sea vents: hot water and minerals emitted from deep sea vents may have provided energy and chemicals needed for early protobionts   ● Simpler hereditary systems (self-replicating molecules) may have preceded nucleic acid genes.

Phylogeny: the evolutionary history of a species ● Systematics: the study of biological diversity in an evolutionary context ● The fossil record: the ordered array of fossils, within layers, or strata, of sedimentary rock ● Paleontologists: collect and interpret fossils

FOSSILS ● A FOSSIL is the remains or evidence of a living thing -bone of an organism or the print of a shell in a rock -burrow or tunnel left by an ancient worm -most common fossils: bones, shells, pollen grains, seeds.

Dimetrodon Rhomaleosaurus victor Tiktaalik Hallucigenia Coccosteus Figure 25.4 Present Dimetrodon Rhomaleosaurus victor 100 mya 1 m 175 Tiktaalik 0.5 m 200 270 300 4.5 cm Hallucigenia Coccosteus cuspidatus 375 400 1 cm Figure 25.4 Documenting the history of life. Dickinsonia costata 500 525 2.5 cm Stromatolites 565 600 Fossilized stromatolite 1,500 3,500 Tappania

Examples of different kinds of fossils PETRIFICATION is the process by which plant or animal remains are turned into stone over time. The remains are buried, partially dissolved, and filled in with stone or other mineral deposits. A MOLD is an empty space that has the shape of the organism that was once there. A CAST can be thought of as a filled in mold. Mineral deposits can often form casts. Thin objects, such as leaves and feathers, leave IMPRINTS, or impressions, in soft sediments such as mud. When the sediments harden into rock, the imprints are preserved as fossils.

PRESERVATION OF ENTIRE ORGANISMS: It is quite rare for an entire organism to be preserved because the soft parts decay easily. However, there are a few special situations that allow organisms to be preserved whole. FREEZING: This prevents substances from decaying. On rare occasions, extinct species have been found frozen in ice. AMBER: When the resin (sap) from certain evergreen trees hardens, it forms a hard substance called amber. Flies and other insects are sometimes trapped in the sticky resin that flows from trees. When the resin hardens, the insects are preserved perfectly.

TAR PITS: These are large pools of tar TAR PITS: These are large pools of tar. Animals could get trapped in the sticky tar when they went to drink the water that often covered the pits. Other animals came to feed on these animals and then also became trapped. TRACE FOSSILS: These fossils reveal much about an animal’s appearance without showing any part of the animal. They are marks or evidence of animal activities, such as tracks, burrows, wormholes, etc.

The fossil record ● Sedimentary rock: rock formed from sand and mud that once settled on the bottom of seas, lakes, and marshes Methods for Dating Fossils: ● RELATIVE DATING: used to establish the geologic time scale; sequence of species ● ABSOLUTE DATING: radiometric dating; determine exact age using half-lives of radioactive isotopes

Where would you expect to find older fossils and where are the younger fossils? Why?

Relative Dating: ● What is an INDEX FOSSIL?  fossil used to help determine the relative age of the fossils around it  must be easily recognized and must have existed for a short period BUT over wide geographical area.

Radiometric Dating: ● Calculating the ABSOLUTE age of fossils based on the amount of remaining radioactive isotopes it contains. Isotope = atom of an element that has a number of neutrons different from that of other atoms of the same element

Radiometric Dating: ● Certain naturally occurring elements / isotopes are radioactive, and they decay (break down) at predictable rates ● An isotope (the “parent”) loses particles from its nucleus to form a isotope of the new element (the “daughter”) ● The rate of decay is expressed in a “half-life”

Daughter Parent

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

Half life= the amount of time it takes for ½ of a radioactive element to decay. To determine the age of a fossil: 1) compare the amount of the “parent” isotope to the amount of the “daughter” element 2) knowing the half-life, do the math to calculate the age!

Parent Isotope Daughter Half-Life Uranium-238 Lead-206 4.5 billion years Uranium-235 Lead-207 704 million years Thorium-232 Lead-208 14.0 billion years Rubidium-87 Strontium-87 48.8 billion years Potassium-40 Argon-40 1.25 billion years Samarium-147 Neodymium-143 106 billion years

Radioactive Dating: Example: Carbon 14 ● Used to date material that was once alive ● C-14 is in all plants and animals (C-12 is too, but it does NOT decay!) ● When an organism dies, the amount of C-14 decreases because it is being converted back to N-14 by radioactive decay

Example: Carbon 14 ● By measuring the amount of C-14 compared to N-14, the time of death can be calculated ● C-14 has a half life of 5,730 years ● Since the half life is considered short, it can only date organisms that have died within the past 70,000 years

What is the half-life of Potassium-40? How many half-lives will it take for Potassium-40 to decay to 50 g? How long will it take for Potassium-40 to decay to 50 g?

What is the half-life of Potassium-40? 1.2 billion years How many half-lives will it take for Potassium-40 to decay to 50 g? 2 half-lives How long will it take for Potassium-40 to decay to 50g? 2.6 billion yrs.

How is the decay rate of a radioactive substance expressed? Equation: A = Ao x (1/2)n A = amount remaining Ao = initial amount n = # of half-lives (**to find n, calculate t/T, where t = time, and T = half-life, in the same time units as t), so you can rewrite the above equation as: A = Ao x (1/2)t/T

½ Life Example #1: ● Nitrogen-13 decays to carbon-13 with t1/2 = 10 minutes. Assume a starting mass of 2.00 g of N-13. A) How long is three half-lives? B) How many grams of the isotope will still be present at the end of three half-lives?

½ Life Example #1: ● Nitrogen-13 decays to carbon-13 with t1/2 = 10 minutes. Assume a starting mass of 2.00 g of N-13. A) How long is three half-lives? (3 half-lives) x (10 min. / h.l.) = 30 minutes

½ Life Example #1: ● Nitrogen-13 decays to carbon-13 with t1/2 = 10 minutes. Assume a starting mass of 2.00 g of N-13. B) How many grams of the isotope will still be present at the end of three half-lives? 2.00 g x ½ x ½ x ½ = 0.25 g

½ Life Example #1: ● Nitrogen-13 decays to carbon-13 with t1/2 = 10 minutes. Assume a starting mass of 2.00 g of N-13. B) How many grams of the isotope will still be present at the end of three half-lives? A = Ao x (1/2)n A = (2.00 g) x (1/2)3 A = 0.25 g

½ Life Example #2: ● Mn-56 has a half-life of 2.6 hr. What is the mass of Mn-56 in a 1.0 mg sample of the isotope at the end of 10.4 hr?

½ Life Example #2: ● Mn-56 has a half-life of 2.6 hr. What is the mass of Mn-56 in a 1.0 mg sample of the isotope at the end of 10.4 hr? A = ? n = t / T = 10.4 hr / 2.6 hr A0 = 1.0 mg n = 4 half-lives A = (1.0 mg) x (1/2)4 = 0.0625 mg

½ Life Example #3: ● Strontium-90 has a half-life of 29 years. What is the mass of strontium-90 in a 5.0 g sample of the isotope at the end of 87 years?

½ Life Example #3: ● Strontium-90 has a half-life of 29 years. What is the mass of strontium-90 in a 5.0 g sample of the isotope at the end of 87 years? A = ? n = t / T = 87 yrs / 29 yrs A0 = 5.0 g n = 3 half-lives A = (5.0 g) x (1/2)3 A = 0.625 g

*The history of living organisms and the history of Earth are inextricably linked:   ● Formation and subsequent breakup of Pangaea affected biotic diversity

BIOGEOGRAPHY: the study of the past and present distribution of species ● Formation of Pangaea - 250 m.y.a. (Permian extinction) ● Break-up of Pangaea – 180 m.y.a. (led to extreme cases of geographic isolation!)  EX: Australian marsupials!

Apparent continental drift results from PLATE TECTONICS

Plate Tectonics: Crust ● At three points in time, the land masses of Earth have formed a supercontinent: 1.1 billion, 600 million, and 250 million years ago ● According to the theory of plate tectonics, Earth’s crust is composed of plates floating on Earth’s mantle Mantle Outer core Inner core

Plate Tectonics: ● Tectonic plates move slowly through the process of continental drift ● Oceanic and continental plates can collide, separate, or slide past each other ● Interactions between plates cause the formation of mountains and islands, and earthquakes

Plate Tectonics: North American Plate Eurasian Plate Juan de Fuca Caribbean Plate Philippine Plate Arabian Plate Indian Plate Cocos Plate South American Plate Pacific Plate Nazca Plate African Plate Australian Plate Figure 25.13 Earth’s major tectonic plates. Scotia Plate Antarctic Plate

Consequences of Continental Drift: ● Formation of the supercontinent Pangaea about 250 million years ago had many effects A deepening of ocean basins A reduction in shallow water habitat A colder and drier climate inland

Present Cenozoic 65.5 Millions of years ago 135 Mesozoic 251 Paleozoic Figure 25.14 Present Cenozoic North America Eurasia 65.5 Africa South America India Madagascar Australia Antarctica Laurasia 135 Millions of years ago Gondwana Mesozoic Figure 25.14 The history of continental drift during the Phanerozoic eon. 251 Pangaea Paleozoic

● The first photosynthetic organisms released oxygen into the air and altered Earth’s atmosphere   ● Members of Homo sapiens have changed the land, water, and air on a scale and at a rate unprecedented for a single species!

(CE)

Figure 2. Sea level is changing Figure 2. Sea level is changing. Observing stations from around the world report year-to-year changes in sea level. The reports are combined to produce a global average time series. The year 1976 is arbitrarily chosen as zero for display purpose. Figure 1. Global warming revealed. Air temperature measured at weather stations on continents and sea temperature measured along ship tracks on the oceans are combined to produce a global mean temperature each year. This 150-year time series constitutes the direct, instrumental record of global warming.

History of Life on Earth: ● Life on Earth originated between 3.5 and 4.0 billion years ago ● Because of the relatively simple structure of prokaryotes, it is assumed that the earliest organisms were prokaryotes *this is supported by fossil evidence (spherical & filamentous prokaryotes recovered from 3.5 billion year old stromatolites in Australia and Africa)

The First Single-Celled Organisms ● The oldest known fossils are stromatolites, rocks formed by the accumulation of sedimentary layers on bacterial mats ● Stromatolites date back 3.5 billion years ago ● Prokaryotes were Earth’s sole inhabitants from 3.5 to about 2.1 billion years ago

 Major Episodes in the History of Life: ● first prokaryotes: 3.5 to 4.0 billion years ago ● photosynthetic bacteria: 2.5-2.7 billion years ago

Photosynthesis and the Oxygen Revolution ● Most atmospheric oxygen (O2) is of biological origin ● This “oxygen revolution” from 2.7 to 2.3 billion years ago caused the extinction of many prokaryotic groups ● Some groups survived and adapted using cellular respiration to harvest energy

(percent of present-day levels; log scale) Figure 25.8 1,000 100 10 1 (percent of present-day levels; log scale) Atmospheric O2 0.1 “Oxygen revolution” 0.01 Figure 25.8 The rise of atmospheric oxygen. 0.001 0.0001 4 3 2 1 0 Time (billions of years ago)

● first eukaryotes: 2 billion years ago ~The oldest unequivocal remains of a diversity of microorganisms occur in the 2.0 BYO Gunflint Chert of the Canadian Shield ~This fauna includes not only bacteria and cyanobacteria but also ammonia consuming Kakabekia and some things that ressemble green algae and fungus-like organisms

The First Eukaryotes ● The oldest fossils of eukaryotic cells date back 2.1 billion years ● Eukaryotic cells have a nuclear envelope, mitochondria, endoplasmic reticulum, and a cytoskeleton ● The endosymbiont theory proposes that mitochondria and plastids (chloroplasts and related organelles) were formerly small prokaryotes living within larger host cells ● An endosymbiont is a cell that lives within a host cell

Endosymbiont Theory: ● 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 ● Serial endosymbiosis supposes that mitochondria evolved before plastids through a sequence of endosymbiotic events

Plasma membrane Cytoplasm DNA Ancestral prokaryote Nucleus Endoplasmic Figure 25.9-1 Plasma membrane Cytoplasm DNA Ancestral prokaryote Nucleus Endoplasmic reticulum Nuclear envelope Figure 25.9 A hypothesis for the origin of eukaryotes through serial endosymbiosis.

heterotrophic eukaryote Figure 25.9-2 Plasma membrane Cytoplasm DNA Ancestral prokaryote Nucleus Endoplasmic reticulum Nuclear envelope Aerobic heterotrophic prokaryote Figure 25.9 A hypothesis for the origin of eukaryotes through serial endosymbiosis. Mitochondrion Ancestral heterotrophic eukaryote

heterotrophic eukaryote Ancestral photosynthetic Figure 25.9-3 Plasma membrane Cytoplasm DNA Ancestral prokaryote Nucleus Endoplasmic reticulum Photosynthetic prokaryote Mitochondrion Nuclear envelope Aerobic heterotrophic prokaryote Figure 25.9 A hypothesis for the origin of eukaryotes through serial endosymbiosis. Mitochondrion Plastid Ancestral heterotrophic eukaryote Ancestral photosynthetic eukaryote

Endosymbiont Theory: ● Key evidence supporting an endosymbiotic origin of mitochondria and plastids: Inner membranes are similar to plasma membranes of prokaryotes Division is similar in these organelles and some prokaryotes These organelles transcribe and translate their own DNA Their ribosomes are more similar to prokaryotic than eukaryotic ribosomes

The Origin of Multicellularity ● The evolution of eukaryotic cells allowed for a greater range of unicellular forms ● A second wave of diversification occurred when multicellularity evolved and gave rise to algae, plants, fungi, and animals

● plants evolved from green algae ● fungi and animals arose from different groups of heterotrophic unicellular organisms

  ● first animals (soft-bodied invertebrates): 550-700 million years ago ● first terrestrial colonization by plants and fungi: 475-500 million years ago  plants transformed the landscape and created new opportunities for all forms of life

The Cambrian Explosion ● The Cambrian explosion refers to the sudden appearance of fossils resembling modern animal phyla in the Cambrian period (535 to 525 million years ago) ● A few animal phyla appear even earlier: sponges, cnidarians, and molluscs ● The Cambrian explosion provides the first evidence of predator-prey interactions

Time (millions of years ago) Sponges Cnidarians Echinoderms Chordates Brachiopods Annelids Molluscs Figure 25.10 Appearance of selected animal groups. Arthropods PROTEROZOIC PALEOZOIC Ediacaran Cambrian 635 605 575 545 515 485 Time (millions of years ago)

The “Big Five” Mass Extinction Events ● In each of the five mass extinction events, more than 50% of Earth’s species became extinct

Macroevolution & Phylogeny Cretaceous mass extinction Asteroid impacts may have caused mass extinction events Cretaceous mass extinction marks boundary between Cretaceous and Tertiary Periods. Permian mass extinction Extinction of >90% of species

Mass extinctions: ● Permian (250 m.y.a.): 90% of marine animals; Pangaea merges ● Cretaceous (65 m.y.a.): death of dinosaurs, 50% of marine species; low angle comet

NORTH AMERICA Chicxulub crater Yucatán Peninsula Figure 25.16 Trauma for Earth and its Cretaceous life.

Consequences of Mass Extinctions ● Mass extinction can alter ecological communities and the niches available to organisms ● It can take from 5 to 100 million years for diversity to recover following a mass extinction ● The percentage of marine organisms that were predators increased after the Permian and Cretaceous mass extinctions ● Mass extinction can pave the way for adaptive radiations

(percentage of marine genera) Time (millions of years ago) 50 40 30 (percentage of marine genera) Predator genera 20 10 Era Period Paleozoic Mesozoic Cenozoic 25.18 Mass extinctions and ecology. E O S D C P Tr J C P N 542 488 444 416 359 299 251 200 145 65.5 Q Permian mass extinction Cretaceous mass extinction Time (millions of years ago)

Adaptive Radiations ● Adaptive radiation is the evolution of diversely adapted species from a common ancestor ● Adaptive radiations may follow Mass extinctions The evolution of novel characteristics The colonization of new regions

Worldwide Adaptive Radiations ● Mammals underwent an adaptive radiation after the extinction of terrestrial dinosaurs ● The disappearance of dinosaurs (except birds) allowed for the expansion of mammals in diversity and size ● Other notable radiations include photosynthetic prokaryotes, large predators in the Cambrian, land plants, insects, and tetrapods

Time (millions of years ago) Ancestral mammal Monotremes (5 species) ANCESTRAL CYNODONT Marsupials (324 species) Eutherians (5,010 species) Figure 25.19 Adaptive radiation of mammals. 250 200 150 100 50 Time (millions of years ago)

Regional Adaptive Radiations ● Adaptive radiations can occur when organisms colonize new environments with little competition ● The Hawaiian Islands are one of the world’s great showcases of adaptive radiation

Close North American relative, the tarweed Carlquistia muirii Figure 25.20 Close North American relative, the tarweed Carlquistia muirii Dubautia laxa KAUAI 5.1 million years MOLOKAI 1.3 million years Argyroxiphium sandwicense OAHU 3.7 million years LANAI MAUI N HAWAII 0.4 million years Figure 25.20 Adaptive radiation on the Hawaiian Islands. Dubautia waialealae Dubautia scabra Dubautia linearis

Evolution is not goal oriented: ● Evolution is like tinkering — it is a process in which new forms arise by the slight modification of existing forms

Evolutionary Novelties ● Most novel biological structures evolve in many stages from previously existing structures ● Complex eyes have evolved from simple photosensitive cells independently many times ● Natural selection can only improve a structure in the context of its current utility

(a) Patch of pigmented cells (b) Eyecup (photoreceptors) Pigmented cells Epithelium Nerve fibers Nerve fibers (c) Pinhole camera-type eye (d) Eye with primitive lens (e) Complex camera lens-type eye Epithelium Cornea Cellular mass (lens) Fluid-filled cavity Cornea Lens Figure 25.26 A range of eye complexity among molluscs. Retina Optic nerve Optic nerve Optic nerve Pigmented layer (retina)

Figure 25.UN11 Appendix A: answer to Test Your Understanding, question 6