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The History of Life. The Fossil Record. Provides evidence about the history of life on Earth. Shows how different groups of organisms, including species have changed over time. The Fossil Record. Paleotologists Study fossils to infer what past life forms were like.
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The Fossil Record • Provides evidence about the history of life on Earth. • Shows how different groups of organisms, including species have changed over time.
The Fossil Record • Paleotologists • Study fossils to infer what past life forms were like. • 99% of all species that ever lived are EXTINCT.
Fossil Formation • Permineralization • Occurs when minerals carried by water are deposited around a hard structure. They may also replace the hard structure itself.
Fossil Formation • Natural Casts • Form when flowing water removes all the original bone or tissue, leaving just an impression in the sediment. Minerals fill the mold, recreating the original shape of the organism.
Fossil Formation • Trace Fossils • Record the activity of an organism. They include nests, burrows, imprints of leaves, and footprints. • Amber-Preserved Fossils • Organisms that become trapped in tree resin that hardens into amber after the tree gets buried under ground.
Fossil Formation • Preserved Remains • Form when an entire organism becomes encased in material such as ice or volcanic ash.
Living Fossils • A living species that has remained unchanged for tens of millions of years Frillshark
Interpreting Fossil Evidence • Relative Dating • The age of a fossil is determined by comparing its placement with that of fossils in other layers of rock.
Interpreting Fossil Evidence • Index Fossils • Are species easily recognized • Found in only a few layers of rock in different geographic locations
Interpreting Fossil Evidence • Radioactive Dating • Radioactive elements break down into non-radioactive elements at a steady rate • Scientists use this to assign absolute ages to rocks • Half-Life • The length of time required for half of the radioactive atoms in a sample to break down.
Interpreting Fossil Evidence • C14 - Taken up by living things while alive • After death, C14 decays to N14 (half-life of 5,730 years.) • C12 is also taken up by living things while alive, and does not decay after death The more C12 there is in a sample compared to C14, the older the sample is.
Geologic Time Scale • Scientists use the geologic time scale to represent evolutionary time. • As geologists studied the fossil record, they found major changes in the fossil animals and plants at specific layers in the rock.
Geologic Time Scale • Eras • Scientists divide the time into eras • Example: • Paleozoic Era—544 mya • Mesozoic Era—245 mya • Cenozoic Era—65 mya • Periods • Eras are subdivided into periods, which range in length from millions of years to less than two million years.
BIG BANG • 12-15 billion years ago, all matter and space was compressed into a hot, dense volume at one single point. • This incredibly hot, dense state lasted only for an instant, and then big bang occurred. • The big bang was the instantaneous distribution of all matter and energy throughout the universe.
Big Bang Evidence Stephen Hawking proposed that black holes formed from gamma ray emissions following the Big Bang. He now suffers from ALS (Lou Gehrig’s Disease). Radio telescopes have detected a relic of the big bang—cooled, diluted background radiation left over from the beginning of time. Telescopes have shown that the universe is continuously expanding.
Conditions on the early Earth Titan, the largest moon of Saturn. • Between 4.6 and 4.5 billion years ago, our Earth was formed. • By studying other proto-planets, scientists theorize that the Earth began as a toxic mixture of hydrogen gas, water, iron, silicates, hydrogen cyanide, ammonia, methane, formaldehyde, and other small organic and inorganic substances.
Conditions on the early Earth The earth did not have a fully functional ozone layer at this point and was constantly bombarded by meteorites, radiation, and other space debris.
Conditions on the early Earth Most of Earth’s early oceans were extremely hot and had magma just beneath the surface. • What about water? • All the water that fell on the molten surface of the Earth would have evaporated at once. • After the crust cooled and became solid, rainfall and runoff eroded mineral salts from rocks.
Abiotic synthesis of organic compounds Cells appeared less than 200 million years after the crust solidified, so complex carbohydrates and lipids, proteins, and nucleic acids must have formed by then.
Abiotic synthesis of organic compounds. • Synthesizing organic compounds requires energy. • On the early Earth, lightning, sunlight, or heat from hydrothermal vents might have fueled the reactions.
Abiotic synthesis of organic compounds Stanley Miller was the first to test the hypothesis that the simple compounds that now serve as the building blocks of life can form by chemical processes.
Abiotic synthesis of organic compounds • Another hypothesis states that simple organic compounds formed in space. • Researchers detect amino acids in interstellar clouds and in come carbon-rich meteorites that have landed on Earth.
Abiotic synthesis of organic compounds • Proteins, DNA, and other complex organic compounds break down in open water. So how did they form? • By one hypothesis, the clay of tidal flats bound and protected the newly forming polymers. • Another hypothesis proposes the first complex biological molecules formed near hydrothermal vents.
Origin of the Plasma Membrane • A current hypothesis states that proto-cells were transitional forms between simple organic compounds and the first living cells.
The Golden Age of Prokaryotes • Fossils indicate that the first cells were like existing prokaryotes; they had no nucleus. • There was very little free oxygen that could attack them. • Anaerobic pathways would allow them to obtain energy from simple organic compounds and mineral ions. • Molecular comparisons of living prokaryotes tell us that some populations diverged not long after life originated. • One lineage gave rise to bacteria, the other archaea.
The Golden Age of Prokaryotes • Microscopically small fossils in 3.5 billion-year-old rocks give clues to what some of the first prokaryotes looked like. • 2.7 billion years ago, colonies of prokaryotes, called stromatolites were abundant. • As cyanobacteria populations increased, so did their waste product, oxygen.
The Oxygen Revolution cyanobacteria • An atmosphere enriched with free oxygen had two irreversible effects. • It helped solidify the ozone layer. • Aerobic respiration evolved and in time became the dominant energy-releasing pathway.
The Rise of Eukaryotes • The first complete eukaryotic fossils are found in rocks dated at 2.1 billion-years-old. • The earliest known eukaryote is Bangiomorphapubescens. A red alga which lived 1.2 billion years ago.
The Rise of Eukaryotes Eukaryotes are characterized by the presence of organelles. So where did they come from?
Where Did Organelles Come From? • Endosymbiotic Theory • Some cells (parasites) struck an uneasy balance with host cells within which they lived. • Over time, they evolved into mitochondria, chloroplasts, and some other organelles.
Evidence of Endosymbiosis • Mitochondria resemble bacteria in size and structure. • Each has its own DNA and divides independently of cell division. • The inner membrane of a mitochondrion resembles a bacterial cell’s plasma membrane. • Its DNA has just a few genes (37).
Precambrian Time • 90% of Earth’s history occurred during the Precambrian • Early life forms developed • Primitive multicellular organisms appeared. • Life existed only in the sea • Most animals animals were soft bodied and left few fossils behind.
Paleozoic Era • Rich fossil evidence shows that early in the Paleozoic Era, there was a diversity of marine life. • During this period, life began to form on dry land, including arthropods, amphibians, reptiles, ferns, and other plants. • Mass Extinction • At the end of the Paleozoic Era about 95% of the life in the ocean disappeared.
Mesozoic Era • Dinosaurs roamed the earth, and flowering plants developed. • Mass Extinction • More than 50% of all plant and animal groups were wiped out, including all of the dinosaurs.
Cenozoic Era • Mammals evolved adaptation that allowed them to live in various environments—on land, in water, and even in the air. • Homo sapiens • Evolved 200,000 years ago
Basic Timeline of Life—Very Approximate Dates 3.8 billion years of simple cells (prokaryotes), 3 billion years of photosynthesis, 2 billion years of complex cells (eukaryotes), 1 billion years of multicellular life, 600 million years of simple animals, 570 million years of arthropods (ancestors of insects, arachnids and crustaceans), 550 million years of complex animals, 500 million years of fish and proto-amphibians, 475 million years of land plants, 400 million years of insects and seeds, 360 million years of amphibians, 300 million years of reptiles, 200 million years of mammals, 150 million years of birds, 130 million years of flowers, 65 million years since the non-avian dinosaurs died out, 2.5 million years since the appearance of the genus Homo, 200,000 years since humans started looking like they do today, 25,000 years since Neanderthals died out.
