Chapter 14 The History of the Earth and the Beginning of Life
Hypothesis of early Earth Very hot surface from colliding meteorites Very hot planet core from radioactive materials Volcanoes spewing lava and gases that helped to form the early atmosphere
Hypothesis of early Earth About 4.4 billion years ago, Earth might have cooled enough for the water in its atmosphere to condense. This might have led to millions of years of rainstorms with lightning, enough rain to fill depressions that became Earth s oceans. The oldest rocks dated are 3.9 million years old.
Spontaneous Generation
Theory of Biogenesis
Miller-Urey experiment showed one possible way for inorganic molecules to form organic molecules. Mixture of gases simulating atmospheres of early Earth Spark simulating lightning storms Condensation chamber Water vapor Cold water cools chamber, causing droplets to form Liquid containing amino acids and other organic compounds
Age of Archaebacteria - more ancient than bacteria
Age of the Bacteria Prokaryotes dominated the Earth for most of its history. Multicellular eukaryotes are less than 1 billion years old. Oldest traces of life: 3.5 3.8 billion years old. Very few rocks available of this age or older. Bacteria can live under a much wider variety of conditions than eukaryotes. They use many different sources of energy and carbon, and they can grew at very high temperatures, high pressures, acidic conditions, etc.
Precambrian 87% of history Oldest fossils resembling cyanobacteria in stromatolites. Stromatolites still form today in Australia from mats of cyanobacteria. The stromatolites are evidence of the existence of photosynthetic organisms on Earth during the Precambrian. Only prokaryotic life found in fossil record
The Onset of Oxygen The atmosphere of the primitive Earth was probably like that of Mars today: nitrogen, carbon dioxide, water vapor, but no free oxygen. Oxygen comes from photosynthesis, specifically, where electrons are extracted from water with the aid of sunlight. The electrons take hydrogen with them, leaving oxygen gas. Cyanobacteria created the oxygen in the atmosphere. About 2 billion years ago, the oxygen level in the atmosphere started to rise. We can detect this geologically: layers of iron oxide on the bottoms of oceans stopped forming when oxygen appeared. Aerobic metabolism, much more efficient than anaerobic, became possible.
Rise of the Eukaryotes Starting with the appearance of an oxygen atmosphere about 2 billion years ago, was dominated by small, soft-bodied eukaryotes. Some were unicellular, others multicellular. Bacteria were still very common, and continue to the present. Eukaryotic fossil cells are identified by their size and surface appearance they look like present day cells. Endosymbiont hypothesis: mitochondria were once free-living bacteria that developed an intracellular symbiosis with a primitive eukaryote. Chloroplasts: another endosymbiont, of a cyanobacteria. Found in plants and algae. and ending with the Cambrian Explosion about 550 million years ago,
Endosymbiotic theory Heterotrophic bacteria have plasmids (DNA loop) & simple ribosomes in their cytoplasm Mitochondria have circular DNA & bacteria-like ribosomes So Eukaryotic cells may have engulfed prokaryotic cells & by mutualism created the first mitochondria.
How eukaryotic cells evolved Chloroplast Aerobic bacteria Ancient Prokaryotes Nuclear envelope evolving Photosynthetic bacteria Mitochondrion Plants and plantlike protists Primitive Photosynthetic Eukaryote Ancient Anaerobic Prokaryote Primitive Aerobic Eukaryote Animals, fungi, and non-plantlike protists
Autotrophic bacteria are Cyanobacteria with chlorophyll So, Eukaryotic cells may have engulfed prokaryotic cyanobacteria & by mutualism created the first chloroplast.
Heterotrophic symbiosis = symbiont produces ATP, host uses ATP, host protects symbiont Autotrophic symbiosis = symbiont produces sugar, host uses sugar, host protects symbiont Relationships may allow host to live longer & reproduce more, thus over time creating more complex eukaryotic cells
Our Story So Far We have come 5/6 of the way through the history of the Earth. Earth forms 4.6 billion years ago Solid surface forms 4 billion years ago Life starts (?) 3.8 billion years ago Age of Bacteria Oxygen atmosphere develops 2 billion years ago. Eukaryotes develop. First multicellular life 650 million years ago.
The Cambrian Explosion About 550 million years ago, there is a sudden appearance of large numbers of multicellular organisms in the fossil record. Rocks older than this appear devoid of fossils (because they are too small to see, and because the multicellular organisms didn t have hard parts to preserve. This sudden appearance of fossils is called the Cambrian explosion. Most of the higher level taxa present today appeared at this time. Cause: a matter of speculation. Most certainly represents a mass extinction.
One prominent type: trilobites, which are extinct ancestors to the crustaceans (crabs, lobsters, shrimp, and insects). Another: nautiloids: molluscs with straight shells that later curled into the nautilus. Cambrian Life
Summary of major events (pg. 397) Era Period Time (millions of years ago) Key Events Cenozoic Quaternary 1.8 present Glaciations; mammals increased; humans Tertiary 65 1.8 Mammals diversified; grasses Mesozoic Cretaceous 145 65 Aquatic reptiles diversified; flowering plants; mass extinction Jurassic 208 145 Dinosaurs diversified; birds Triassic 245 208 Dinosaurs; small mammals; cone-bearing plants Paleozoic Permian 290 245 Reptiles diversified; seed plants; mass extinction Carboniferous 363 290 Reptiles; winged insects diversified; coal swamps Devonian 410 363 Fishes diversified; land vertebrates (primitive amphibians) Silurian 440 410 Land plants; land animals (arthropods) Ordovician 505 440 Aquatic arthropods; mollusks; vertebrates (jawless fishes) Precambrian Time Cambrian 544 505 650 544 Marine invertebrates diversified; most animal phyla evolved Anaerobic, then photosynthetic prokaryotes; eukaryotes, then multicellular life
HOW DO WE KNOW THIS STUFF???
The Fossil Record Provides evidence about the history of life on Earth. It also shows how different groups of organisms, including species, have changed over time.
Categories of fossil types (393) mold cast imprint hollow impression of a living thing in rock solid mineral deposit that filled a mold, leaving a copy of the living thing an impression in rock made by a living thing during its life activities petrification whole animal plant or animal tissue replaced by minerals an entire plant or animal encased and preserved in ice, sap, or another material
How fossils are formed Water carries small rock particles to lakes and seas. Dead organisms are buried by layers of sediment, which forms new rock. The preserved remains may later be discovered and studied.
Principle of Superposition In an undisturbed sequence of sedimentary rocks, the oldest rocks are on the bottom with the most recent on top.
Relative vs. Absolute Dating Comparing Relative and Absolute Dating of Fossils Can determine Is performed by Drawbacks Relative Dating Age of fossil with respect to another rock or fossil (that is, older or younger) Comparing depth of a fossil s source stratum to the position of a reference fossil or rock Imprecision and limitations of age data Absolute Dating (radiometric) Age of a fossil in years Determining the relative amounts of a radioactive isotope and nonradioactive isotope in a specimen Difficulty of radioassay laboratory methods
Radiometric Dating
What has been learned from fossils Paleontologists estimate that about 95% species are extinct from life s origins. Climate and ancient geography can be determined from fossils. Several episodes of mass extinction that fall between time divisions mass extinction: an event that occurs when many organisms disappear from the fossil record almost at once The existence of a unified landmass called Pangea
Continental drift Earth s continents have moved during Earth s history and are still moving today at a rate of about six centimeters per year. The theory for how the continents move is called plate tectonics. http://www.youtube.com/watch?v=gyvs_yh6dtk
Other Evidence From Fossils Homologous Structures
Embryological Evidence
2 Types of Evolution Microevolution Small scale Macroevolution Large scale To understand this better, you must know what a species is: One group of interbreeding organisms found in one place at one time.
Microevolution Small scale evolution occurring over a relatively short period of time = changes within one population Includes 4 topics Mutation Selection Gene Pool Genetic Drift
Macroevolution Large-scale evolutionary patterns and processes that occur over long periods of time = speciation (making a new species) Includes 6 topics: Extinction Adaptive radiation Convergent evolution Divergent evolution Punctuated equilibrium Changes in developmental genes
Darwin believed that organisms evolved gradually. (gradualism) Niles Eldredge and Stephen Jay Gould believed punctuated equilibrium is how organisms evolved, periods of rapid evolution followed by periods of stasis. BOTH REPRESENT DIVERGENT EVOLUTOIN Patterns of evolution
Convergent Evolution Adaptive radiation can produce unrelated organisms that look similar due to similar environments.
Adaptive Radiation Single species or small groups of species evolved into diverse forms living in different ways.
Coevolution The process by which two species evolve in response to changes in each, other over time. http://ecology.botany.ufl.edu/ ecologyf02 Example: This butterfly acquires a cardiac glycoside from members of the genus Asclepias. Because of their milky sap, these are commonly referred to as milkweed plants. The plants produce this toxin as a defense against herbivory, but the Monarch has the ability to sequester the toxin in fatty tissues so that it makes the butterfly unpalatable while not poisoning the butterfly.