Chapter 12 History of Life

12-1 How Did Life Begin How old is the Earth? 4.5 to Billion Year Old! How do we know?

Radiometric Dating Calculating the age of an object by measuring the proportions of the radioactive isotopes of certain elements Radioisotopes are unstable elements They decay, or break apart

We measure decay using the half-life of the element Half-life means how long it takes for half the atoms of a given radioisotope to decay Different half-life # for different elements

Life From ?? Life on planet Earth came from two possible sources. Most likely is Spontaneous Origin, life developing from organic molecules reacting with the environment Where do we get organic molecules?

Deep Sea Hydrothermal Vents Extraterrestrial Seeding Frozen Ocean Theory

Conditions of Early Earth

THE EARLY ATMOSPHERE Possible gasses: H2O, NH3, CH4, H2, CO2. Ammonia would have broken down: 2NH3 into N2 + 3H2 (escaped to space) Final content was probably H2O vapor, CO2 and CO, N2 (80%). NO OXYGEN

NO ENZYMES WERE PRESENT REQUIREMENTS FOR LIFE Lack of oxygen (reducing atmosphere). Appropriate chemicals (water, organic and inorganic molecules) Sources of energy (U.V., heat, lightning) Great amounts of time NO ENZYMES WERE PRESENT REACTIONS WERE SLOW

Oparin and Haldane 1920s Hypothesized steps of chemical evolution from primitive earth conditions. Led to the Primordial Soup Model

Miller and Urey, 1953 Tested Oparin and Haldane’s hypothesis. Experiment - to duplicate primitive earth conditions in the lab.

Results Organic monomers formed including Amino Acids.

Problems With The Model No ozone to protect the gases in the atmosphere UV radiation would have destroyed ammonia and methane

Bubble Model Louis Lerman suggested that the key process to form organic chemicals occurred at the ocean’s surface

What About Genetic Information?

Genetic Information DNA  RNA  Protein Too complex for early life. Other forms of genetic information?

RNA Hypothesis RNA as early genetic information.

Rationale RNA polymerizes easily. RNA can replicate itself. RNA can catalyze reactions including protein synthesis.

What About Cell Membranes? Short chains of amino acids can lead to microspheres

Coacervates Colloidal droplets of proteins, nucleic acids and sugars surround by a water shell. Will form spontaneously from abiotically produced organic compounds.

12-2 Development of Life Oldest fossils are 3.5 Billion Years Old They are prokaryotes First prokaryotes were heterotrphs then autotrophs Cyanobacteria were among the first photosynthetic bacteria Responsible for free oxygen in the atmosphere

Eubacteria are prokaryotes that contain peptidoglycan Archeabacteria are prokaryotes that do not contain peptidoglycan Evidence indicates that archeabacteria were the 1st group to evolve

1st Eukaryotes Appear about 1.5 Billion Years Ago Mitochondria and Chloroplast appearance explained by endosymbiosis These organelles are descended from aerobic, symbiotic eubacteria Both organelles have their own DNA

Multicellular Forms of Life Have developed many times Life grouped into 6 Kingdoms Eubacteria and Archeabacteria are single celled Fungi, Plants, Protists, and Animals have multicellular organisms

Cambrian Explosion When the most of the current body plans 1st appear in the fossil record Most famous fossil find from this time period was the Burgess Shale

Mass Extinctions Impact life because it reduces the amount of competition for resources Allows for adaptive radiation to occur Almost every time period has one!

12-3 Progression of Life Once the ozone layer formed, life could invade the land Ozone began to form around 2.5 BYA Is formed when oxygen gas (O2) becomes O3 from the radiation of the sun

1st multicellular land organisms were plants and fungi (Around 430 MYA) Created a mutualistic realationship Means both benefit Called mycorrhizae

Arthropods were the first animals to invade land (After the plants and fungi) Arthropods have a hard exoskeleton and jointed limbs Examples include lobsters, crabs, insects, arachnids, scorpions

Vertebrates followed arthropods Vertebrates have a backbone First ones were small, jawless fish in the oceans Then came the jawed fishes

Amphibians were the 1st land vertebrates Could breath air Had better adaptations for thriving on land than fish

Reptiles evolved from amphibians Even more adapted to life on land Had water tight skin, and shelled eggs

Mammals and Birds evolved from reptiles Better adapted to the changes in the climate at the end of the Cretaceous

Time Periods in Order Cambrian (Oldest) Ordovician Silurian Devonian Carboniferous Permian

Triassic Jurassic Cretaceous Tertiary Quaternary (Present)