The History of Life Chapter 17

Fossils  Preserved traces and remains of ancient life.

The Fossil Record  Paleontologists study ancient life through fossils.  They make inferences about past life and group similar organisms together to create the fossil record.  Fossils show that more than 99% of all living species that have ever existed have become extinct.

How Fossils Form  Is the fossil record complete?  Many more organisms die without leaving traces than those that do.  Most fossils form in sedimentary rock.

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. Section 17-1 Figure 17-2 Formation of a Fossil

Interpreting Fossil Evidence  Relative Dating –  Estimates a fossil’s age by comparing to other fossils present in the same layer.  Index fossils identify a particular era  Absolute (Radioactive) Dating –  A more exact method of determining a fossil’s age by determining the percent of a radioactive element left in the sample.

Relative Dating

Can determine Is performed by Drawbacks Absolute Dating Comparing Relative and Absolute Dating of Fossils Section 17-1 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

Geologic Time Scale  Represents evolutionary time.  Precambrian time - before complex life  Eras – after Precambrian time.  Paleozoic – fish and amphibiams  Mesozoic – age of dinosaurs  Cenozoic – age of mammals

Section 17-3 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)

Earth’s Early History  Ancient earth was hostile.  Poisonous atmosphere ; no oxygen  Oceans were a “hot thin soup”  UV radiation, lightening, volcanos…  So how did life begin?

Mixture of gases simulating atmospheres of early Earth Spark simulating lightning storms Condensation chamber Cold water cools chamber, causing droplets to form Water vapor Liquid containing amino acids and other organic compounds Section 17-2 Figure 17-8 Miller-Urey Experiment Stanley Miller recreated early earth’s atmosphere Made simple organic molecules (amino acids…) The first organic molecules…

Coacervates Proteinoid microspheres may have formed in shallow pools as precursors to cells.

Evolution of RNA and DNA

Stromatolites  Ancient prokaryotes added oxygen to the atmosphere.  The rise of oxygen caused drove some life forms to extinction while others evolved.

Aerobic bacteria Ancient Prokaryotes Ancient Anaerobic Prokaryote Primitive Aerobic Eukaryote Primitive Photosynthetic Eukaryote Chloroplast Photosynthetic bacteria Nuclear envelope evolving Mitochondrion Plants and plantlike protists Animals, fungi, and non-plantlike protists Figure Endosymbiotic Theory Endosymbiotic Theory – origin of eukaryotic cells This theory proposes that eukaryotic cells arose from symbiotic relationships between bacteria and cells.

Sexual Reproduction and Multicellularity This ancient jellyfish was an early multicellular animal. With the advent of sexual reproduction the rate of evolution took off.

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.

Heterotroph Hypothesis  The first cells were…  Heterotrophs  autotrophs  Anaerobic  aerobic  Unicellular  multicellular  Asexual  sexual

Patterns of Evolution  Extinction  The last member of a species dies….(failure of a species to adapt)

Patterns of Evolution  Adaptive radiation  An ancestral form evolves into diverse forms through natural selection

Patterns of Evolution  Convergent evolution  Unrelated species evolve similar adaptations due to similar environments

Patterns of Evolution  Coevolution - Evolution of two different species in response to each other: symbiosis

Patterns of Evolution  Gradualism –  A slow and steady rate of evolution

Patterns of Evolution  Punctuated equilibrium –  Periods of rapid evolution followed by long stretches of stability

Section 17-4 Flowchart that are can undergo inunder formin Species Unrelated Related Inter-relationshiops Similar environments Intense environmental pressure Small populations Different environments Coevolution Convergent evolution Extinction Punctuated equilibrium Adaptive radiation