Presentation on theme: "Conditions on early Earth made the origin of life possible"— Presentation transcript:
1Conditions on early Earth made the origin of life possible Synthesis of Organic Compounds on Early EarthEarth formed about 4.6 billion years ago (bya)The Oparin-Haldane hypothesis stated that Earth’s early atmosphere was a reducing (e- adding) environment. Organic molecules could be synthesized from inorganic molecules or small molecules and the energy required for this synthesis could come from lightning and UV light.Stanley Miller and Harold Urey’s experiment in 1953 demonstrated that organic molecules like amino acids could be synthesized from inorganic molecules like those found in the early Earth.
2Early Atmosphere (Notice what is NOT on this list) Water vapor (condensed into oceans as the earth cooled)Nitrogen and nitrogen oxidesCarbon dioxideMethaneAmmoniaHydrogenHydrogen sulfideOriginally thought to be a reducing atmosphere
3Miller and Urey’s Experiment ELECTRICITY!!!Organic molecules like amino acids
4The precambrian world might have looked like this – 3 billion years ago
5Are molecules like amino acids sufficient for the emergence of life?? Amino acid polymers have been found to be synthesized without enzymes. Clay and sand (abiotic) have been shown to “grow” these polymers.What about replication and metabolism? Hereditary material?
6Nucleotides arranging them on clay It’s an RNA world, baby!Ribozymes are RNA catalystsNucleotides arranging them on clayScience 22 September 2006: Vol no. 5794, p. 1700
7RNA worldThe first genetic material was probably self-replicating, catalytic RNA not DNA;In “RNA world”, RNA could have provided the template on which DNA was assembledOnce DNA appeared “RNA world” gave way to “DNA world”The first organisms were not photosynthetic; they were probably heterotrophic
8Protobionts, collections of abiotically produced molecules surrounded by a membrane-like structures Liposomes can form when lipids or other organic molecules are added to water.Have a bilayerCan undergo osmosisCan “reproduce”
9Protocell (Protobiont) Fatty acid membrane with ribozymes inside
10The Fossil Record documents the history of life PresentDimetrodonCoccosteus cuspidatusFossilizedstromatoliteStromatolitesTappania, aunicellulareukaryoteDickinsoniacostataHallucigeniaCasts ofammonitesRhomaleosaurus victor,a plesiosaur100 million years ago2001753002704003755005255656003,500 1,5002.5 cm4.5 cm1 cmKeep in mind that it is an incomplete chronicle or evolutionary change. WHY?The fossil record is biased in favor of species that existed for a long period of time, were abundant and wide-spread, and had hard shells
11How do we determine the age of fossils? The order of fossils in rock strata tells us the sequence in which the fossils were laid down – their relative ages – it does not tell us their absolute ages.SO…. We use radiometric dating to determine actual age of fossils.
12Radiometric Dating – each isotope has a fixed rate of decay
13Radiometric datingFossils contain isotopes of elements that accumulated in the organisms when they were alive.For example: C-12 (most common isotope) and C-14 are both found in living organisms. When an organism dies it stops accumulating this carbon and the C-12 levels do not change over time. BUT – the C-14 isotope begins to decay into N-14.By measuring the ratio of carbon-14 to carbon-12, we can determine a fossil’s age
16Three-domain system Look at how this evolution happened! Prokaryotes ExtremophilesEukaryotesLook at how this evolution happened!
17Cyanobacterium - Anabaena Early cells were heterotrophs – but this probably added extreme selective pressure on these cells due to famine.This selected for cells that could produce their own food - autotrophs
18When photosynthesis is based around water, it produces a significant by-product: oxygen. Since oxygen was highly toxic to the cyanobacteria producing it, they were forced to evolve means of protecting themselves from it, primarily by excreting it as a gas.
19Cyanobacteria converted the reducing environment of early Earth into an oxidizing one Their success in this led to the steady but gradual pumping of oxygen into the Earth's atmosphere.Cyanobacteria are the only O2-releasing prokaryotesAtmospheric O2 is generated by photosynthetic organisms in the water-splitting step
20Cross section of microbial mats showing layers of pigmented bacteria
21Some bacterial mats form rock-like structures called stromatolites Shark Bay, Western Australia
22These stromatolites in Morocco formed at the bottom of a sea about 600 million years ago
23This precambrian stromatolite from the Ozarks is over 1 This precambrian stromatolite from the Ozarks is over 1.5 billion years oldSee the layer of cyanobacteria (photosynthetic) near the top of the image
24This stromatolite is about 3.5 million years old
25Three-domain system Look at how this evolution happened! Prokaryotes ExtremophilesEukaryotesLook at how this evolution happened!
26Early prokaryotes may have arisen near hydrothermal vents Hydrothermal vents are rich in sulphur and iron-containing compounds needed for ATP synthesis. Temperatures can reach 120 C.
27Hot springs in Yellowstone National Park – pigmented bacterial mats
28Three-domain system Look at how this evolution happened! Prokaryotes ExtremophilesEukaryotesLook at how this evolution happened!
29Eukaryotic cells arose from symbiotic interactions about 2 Eukaryotic cells arose from symbiotic interactions about 2.1 billion years ago
30Mitochondria and chloroplasts have their own DNA An anaerobic cell that contained an aerobe would have an advantage.What do these two types of cells become millions of years later?
31Evidence for endosymbiosis MembranesDNAReproduction
32Origin of Multicellularity These early organisms lived 1.5 billion years ago.“Snowball Earth Hypothesis” states that ice ages caused glaciers to cover most of the surface of the Earth and that life would have been limited to the deep sea or hot springs or equatorial regions without ice cover.When “snowball Earth” thawed roughly 565 mya, the fossil record shows a rapid diversification of life
33The first multicellular organisms were colonies, collections of autonomously replicating cells.
34Cambrian – large changes in seawater composition occurred in this period, e.g.extreme fluctuations in carbon, sulphur, and strontiumDuring this period extremely varied complex animal forms existed.
35Cambrian Explosion – 535-525 mya Pre-cambrian:Cnideria, sponges and molluscsHerbivores, filter-feeders or scavengers, not huntersSoft-bodiedCambrian Explosion:Short period of time (10 my)Predators became prevalent – teeth, clawsDefensive adaptations – sharp spines, body armorLarger organisms
37Colonization of LandCyanobacteria and other photosynthetic prokaryotes coated damp terrestrial surfaces well over 1 billion years ago.Fungi, plants, and animals, did not begin to colonize land until about 500 million years ago.Plants evolution – vascular system, waxy cuticle, reproductionMutualistic associations between fungi and plants developed during this timeArthropods rule!Tetrapods
38Earth’s major crustal plates are still changing constantly – they are floating on the hot molten underlying mantleNot shown: A new plate is forming between East Africa and the rest of the continent
39The earth is still changing San Andreas fault east of San Luis Obispo
40Continental Drift Present Cenozoic 65.5 Millions of years ago 135 Mesozoic251
41Volcanoes shape the earth Bora boraIcelandic island at the border between the Eurasian and the North American plates, which are still moving apart.
46Three genera of lungfish are alive today; each is found on a single continent This whopper is from Australia
47Of the 5 major mass extinctions documented by the fossil record two are best studied – Permian and CretaceousThe Permian mass extinction eliminated more than 97% of marine life.
48Permian extinction was a period of global warming Mass Extinction 250 Million Years Ago Sparked Dramatic Shift To Complex Marine Ecosystemsthe event wiped out an estimated 95% of marine species and 70% of land specieschanged the basic ecology of the world's oceansProbably took place in less than 5 million yearsMost extreme period of volcanism in last half billion years in area that is now Siberia
49Complex marine ecosystems millions of years after the Permian extinction displaced the simpler ecosystems that had existed previously.
50Cretaceous Mass Extinction (65 mya) Extinguish more than half of marine speciesEliminated most dinosaursEarly primates survivedCloud from possible meteor would have blocked sunlight and disturbed climate
51Creatures before and after the Cretaceous mass extinction (65 mya)
52Ecological Consequences of Mass Extinctions Reduces a complex ecological community to a much reduced one; takes at least million years to rediversify, sometimes 100 millionLineages (species) that disappear do not reappearAfter the Permian and Cretaceous mass extinctions, percentage of marine predators increased substantiallyMass extinctions can allow new groups of organisms to become dominant species
53Diversity of life has increased as a consequence of adaptive radiations Results in new species whose adaptations allow them to fill different ecological niches
54Adaptive Radiation of mammals AncestralmammalMonotremes(5 species)ANCESTRALCYNODONTMarsupials(324 species)Dwarf Cloud RatEutherians(placentalmammals;5,010 species)25020015010050Millions of years ago