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Conditions on early Earth made the origin of life possible

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Presentation on theme: "Conditions on early Earth made the origin of life possible"— Presentation transcript:

1 Conditions on early Earth made the origin of life possible
Synthesis of Organic Compounds on Early Earth Earth 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.

2 Early Atmosphere (Notice what is NOT on this list)
Water vapor (condensed into oceans as the earth cooled) Nitrogen and nitrogen oxides Carbon dioxide Methane Ammonia Hydrogen Hydrogen sulfide Originally thought to be a reducing atmosphere

3 Miller and Urey’s Experiment
ELECTRICITY!!! Organic molecules like amino acids

4 The precambrian world might have looked like this – 3 billion years ago

5 Are 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?

6 Nucleotides arranging them on clay
It’s an RNA world, baby! Ribozymes are RNA catalysts Nucleotides arranging them on clay Science 22 September 2006: Vol no. 5794, p. 1700

7 RNA world The first genetic material was probably self-replicating, catalytic RNA not DNA; In “RNA world”, RNA could have provided the template on which DNA was assembled Once DNA appeared “RNA world” gave way to “DNA world” The first organisms were not photosynthetic; they were probably heterotrophic

8 Protobionts, 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 bilayer Can undergo osmosis Can “reproduce”

9 Protocell (Protobiont)
Fatty acid membrane with ribozymes inside

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

11 How 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.

12 Radiometric Dating – each isotope has a fixed rate of decay

13 Radiometric dating Fossils 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

14 Table 25-1a

15 Table 25-1b

16 Three-domain system Look at how this evolution happened! Prokaryotes
Extremophiles Eukaryotes Look at how this evolution happened!

17 Cyanobacterium - 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

18 When 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.

19 Cyanobacteria 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 prokaryotes Atmospheric O2 is generated by photosynthetic organisms in the water-splitting step

20 Cross section of microbial mats showing layers of pigmented bacteria

21 Some bacterial mats form rock-like structures called stromatolites
Shark Bay, Western Australia

22 These stromatolites in Morocco formed at the bottom of a sea about 600 million years ago

23 This precambrian stromatolite from the Ozarks is over 1
This precambrian stromatolite from the Ozarks is over 1.5 billion years old See the layer of cyanobacteria (photosynthetic) near the top of the image

24 This stromatolite is about 3.5 million years old

25 Three-domain system Look at how this evolution happened! Prokaryotes
Extremophiles Eukaryotes Look at how this evolution happened!

26 Early 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.

27 Hot springs in Yellowstone National Park – pigmented bacterial mats

28 Three-domain system Look at how this evolution happened! Prokaryotes
Extremophiles Eukaryotes Look at how this evolution happened!

29 Eukaryotic cells arose from symbiotic interactions about 2
Eukaryotic cells arose from symbiotic interactions about 2.1 billion years ago

30 Mitochondria 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?

31 Evidence for endosymbiosis
Membranes DNA Reproduction

32 Origin 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

33 The first multicellular organisms were colonies, collections of autonomously replicating cells.

34 Cambrian – large changes in seawater composition occurred in this period, e.g.extreme fluctuations in carbon, sulphur, and strontium During this period extremely varied complex animal forms existed.

35 Cambrian Explosion – 535-525 mya
Pre-cambrian: Cnideria, sponges and molluscs Herbivores, filter-feeders or scavengers, not hunters Soft-bodied Cambrian Explosion: Short period of time (10 my) Predators became prevalent – teeth, claws Defensive adaptations – sharp spines, body armor Larger organisms

36 (a) Two-cell stage (b) Later stage 150 µm 200 µm

37 Colonization of Land Cyanobacteria 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, reproduction Mutualistic associations between fungi and plants developed during this time Arthropods rule! Tetrapods

38 Earth’s major crustal plates are still changing constantly – they are floating on the hot molten underlying mantle Not shown: A new plate is forming between East Africa and the rest of the continent

39 The earth is still changing
San Andreas fault east of San Luis Obispo

40 Continental Drift Present Cenozoic 65.5 Millions of years ago 135
Mesozoic 251

41 Volcanoes shape the earth
Bora bora Icelandic island at the border between the Eurasian and the North American plates, which are still moving apart.

42 Active volcano in Hawaii

43 Pangaea had split into Laurasia and Gondwana by the middle of the Mesozoic era (135 mya)
Fish and large land-dwelling reptiles existed at this time

44 Lungfish - a relative of early tetrapod fish first appeared in the early Devonian (400mya)

45 Distribution of lungfish

46 Three genera of lungfish are alive today; each is found on a single continent
This whopper is from Australia

47 Of the 5 major mass extinctions documented by the fossil record two are best studied – Permian and Cretaceous The Permian mass extinction eliminated more than 97% of marine life.

48 Permian extinction was a period of global warming
Mass Extinction 250 Million Years Ago Sparked Dramatic Shift To Complex Marine Ecosystems the event wiped out an estimated 95% of marine species and 70% of land species changed the basic ecology of the world's oceans Probably took place in less than 5 million years Most extreme period of volcanism in last half billion years in area that is now Siberia

49 Complex marine ecosystems millions of years after the Permian extinction displaced the simpler ecosystems that had existed previously.

50 Cretaceous Mass Extinction (65 mya)
Extinguish more than half of marine species Eliminated most dinosaurs Early primates survived Cloud from possible meteor would have blocked sunlight and disturbed climate

51 Creatures before and after the Cretaceous mass extinction (65 mya)

52 Ecological Consequences of Mass Extinctions
Reduces a complex ecological community to a much reduced one; takes at least million years to rediversify, sometimes 100 million Lineages (species) that disappear do not reappear After the Permian and Cretaceous mass extinctions, percentage of marine predators increased substantially Mass extinctions can allow new groups of organisms to become dominant species

53 Diversity of life has increased as a consequence of adaptive radiations
Results in new species whose adaptations allow them to fill different ecological niches

54 Adaptive Radiation of mammals
Ancestral mammal Monotremes (5 species) ANCESTRAL CYNODONT Marsupials (324 species) Dwarf Cloud Rat Eutherians (placental mammals; 5,010 species) 250 200 150 100 50 Millions of years ago


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