Early Ideas of Life

Early Environment Earth is about 4.6 billion years old Inhospitable environment Volcanoes spewed gases that helped form early atmosphere Gases included: water vapor, carbon dioxide and nitrogen Very little oxygen present

Early Environment About 3.9 million years ago: Earth cooled enough for water vapor to condense Millions of years of rainstorms that included lightning Between million years, first organisms appeared

Rocks Tell a lot about history of Earth and life 99% of all species on Earth are extinct

Fossils Evidence of previously living organisms Occur in sedimentary rock (layers) Usually near water Gentle process

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. Figure 17-2 Formation of a Fossil Formation of a Fossil

Fossils Paleontologist – study ancient life using layers of earth and fossils Make conclusions: Climate What organism ate Geography of land Modern relatives

Relative Dating Can determine Is performed by Drawbacks Absolute Dating Comparing Relative and Absolute Dating of Fossils Compare/Contrast Table Imprecision and limitations of age data Difficulty of radioassay laboratory methods Comparing depth of a fossil’s source stratum to the position of a reference fossil or rock Determining the relative amounts of a radioactive isotope and nonradioactive isotope in a specimen Age of fossil with respect to another rock or fossil (that is, older or younger) Age of a fossil in years Compare/Contrast Table

Geologic Time Scale - Eras Precambrian – prokaryotes and eukaryotes Paleozoic – first vertebrates and invertebrates, fish, amphibians, reptiles, evergreens dominant Mesozoic – dinosaurs, mammals, birds, flowering plants dominant Cenozoic – placental mammals, humans

Geologic Time Scale with Key Events Glaciations; mammals increased; humans Mammals diversified; grasses Aquatic reptiles diversified; flowering plants; mass extinction Dinosaurs diversified; birds Dinosaurs; small mammals; cone-bearing plants Reptiles diversified; seed plants; mass extinction Reptiles; winged insects diversified; coal swamps Fishes diversified; land vertebrates (primitive amphibians) Land plants; land animals (arthropods) Aquatic arthropods; mollusks; vertebrates (jawless fishes) Marine invertebrates diversified; most animal phyla evolved Anaerobic, then photosynthetic prokaryotes; eukaryotes, then multicellular life Cenozoic Mesozoic Paleozoic Precambrian Time Quaternary Tertiary Cretaceous Jurassic Triassic Permian Carboniferous Devonian Silurian Ordovician Cambrian 1.8–present 65– –65 208– – – – – – – – –544 Key EventsEraPeriodTime (millions of years ago) Geologic Time Scale

Early Life Ideas People thought that bacteria came from air, maggots came from meat, and baby mice came from sacks of grain Spontaneous generation is the idea that living things can come from nonliving things.

Early Life Ideas Spontaneous generation Living things come from non-living things Redi (1668) disproved: “meat in a jar” Vital force in the air Idea that microorganisms arise from air Pasteur (1880s) disproved: broth in a swan- necked flask Biogenesis: Life comes from life

Modern Life Ideas 2 things had to happen before life appeared: Organic molecules had to form These molecules had to organize into proteins, carbohydrates, and nucleic acids

Modern Life Ideas Oparin (1930s) - primordial soup hypothesis Energy from the sun, lightning & heat triggered chemical reactions to change gases into small organic compounds

Miller-Urey Experiment Experiments tested Oparin’s hypothesis They were able to produce amino acids and other organic compounds in the lab Later experiments showed that amino acids heated w/o oxygen would form proteins

The First Organic Molecules Miller and Urey’s Experiment Condensation chamber Mixture of gases simulating atmosphere of early Earth Spark simulating lightning storms Water vapor Liquid containing amino acids and other organic compounds Cold water cools chamber, causing droplets to form.

Formation of Microspheres proteinoid microspheres - large organic molecules form tiny bubbles called under certain conditions are not cells have selectively permeable membranes can store and release energy. Hypotheses suggest that structures similar to microspheres might have acquired more characteristics of living cells.

The Puzzle of Life's Origin RNA and the Origin of Life Abiotic “stew” of inorganic matter Simple organic molecules RNA nucleotides RNA able to replicate itself, synthesize proteins, and function in information storage DNA functions in information storage and retrieval RNA helps in protein synthesis Proteins build cell structures and catalyze chemical reactions

Free Oxygen Oxygen in the atmosphere drove some life forms to extinction Other life forms evolved new, more efficient metabolic pathways that used oxygen for respiration.

Endosymbiosis Margulis (1960s) - Endosymbiotic theory Eukaryotes came from symbiotic relationships between prokaryotes Large prokaryotes ingest small prokaryotes --> plant and animal cells

Endosymbiotic Theory Mitochondrion Aerobic bacteria Nuclear envelope evolving Ancient Prokaryotes Plants and plantlike protists Primitive Photosynthetic Eukaryote Primitive Aerobic Eukaryote Ancient Anaerobic Prokaryote Chloroplast Animals, fungi, and non-plantlike protists Photosynthetic bacteria

Origin of Eukaryotic Cells Ancient Anaerobic Prokaryote Nuclear envelope evolving Aerobic bacteria Ancient Prokaryotes

Origin of Eukaryotic Cells Prokaryotes that use oxygen to generate energy-rich molecules of ATP evolved into mitochondria. Mitochondrion Primitive Aerobic Eukaryote

Origin of Eukaryotic Cells Primitive Photosynthetic Eukaryote Chloroplast Photosynthetic bacteria Prokaryotes that carried out photosynthesis evolved into chloroplasts.

Concept Map Evolution of Life Early Earth was hot; atmosphere contained poisonous gases. Earth cooled and oceans condensed. Simple organic molecules may have formed in the oceans.. Small sequences of RNA may have formed and replicated. First prokaryotes may have formed when RNA or DNA was enclosed in microspheres. Later prokaryotes were photosynthetic and produced oxygen. An oxygenated atmosphere capped by the ozone layer protected Earth. First eukaryotes may have been communities of prokaryotes. Multicellular eukaryotes evolved. Sexual reproduction increased genetic variability, hastening evolution.