Transcript File
The History of Life & The Theory of Evolution J. Quigley 2008 Early History of Earth Early earth was inhospitable: very hot with volcanoes spewing lava and gases The gases from the volcanoes helped create the ancient atmosphere which probably had little oxygen, a lot of water vapor, carbon dioxide and nitrogen. Early Earth Around 3.9 billion years ago Earth might have cooled enough for water in the atmosphere to condense. The condensing water might have led to millions of years of rainstorms and lightning creating the oceans Some scientists believe between 3.9 and 3.5 billion years ago, the first organisms appeared in the ocean History in Rocks: Scientists can’t be certain how earth formed, but rocks help create hypotheses Fossils are clues to the past. A fossil is evidence of an organism that lived long ago. Fossils can form many different ways Types of fossils Trace Fossils- a marking left by an animal like a footprint, trail or burrow. Cast Fossils- when minerals in rocks fill the space left by an organism, they make a replica of the organism Types of fossils Imprint Fossils- thin objects such as a leaf fall into sediment, they leave an imprint when the sediment hardens into rock. Mold Fossils- when an organism is buried in the sediment and then decays leaving an empty space Types of fossils Petrified Fossils- Minerals sometimes penetrate and replace the hard parts of an organism, producing copies of them Amber Preserved and Frozen Fossils- At times an entire organism is trapped in ice or tree sap that hardens into amber Paleontologists- Detectives of the past Studying fossils is like solving a mystery. Paleontologists study ancient life and use fossils to try to understand the events that happened long ago. Fossils can explain where the organism lived, what it ate, size, and even sometimes behaviors. Fossils can also help explain ancient climate and geography Sedimentary Rock For a fossil to form, organisms usually have to be buried in a small particles of mud, sand or clay soon after they die. These particles compress over time and harden into sedimentary rock (Look at page 381) Dating Fossils: (not “dating” but how old are they) ha-ha! Relative DatingFossils that are found deeper in the ground are older than ones found closer to the surface. This is the principal of geological law. Layering of rocks tells scientists which fossils are older than others Radiometric DatingScientists use isotopes in the fossils to determine the exact age of the fossil. Isotopes “decay” at specific a speed, so they can look at the isotopes and determine the age of something. A Trip Through Time The geologic time scale is divided into four eras: Precambrian, Paleozoic, Mesozoic and Cenozoic. Each era is divided into smaller amounts of time called periods Time scale is distinguished by the organisms that lived during the time period. Geologic Time Scale Geologic Time Scale The fossil record indicates that there were several occurrences of mass extinction that fall between the time divisions Mass extinction is an event where entire groups of organisms disappear from the fossil record almost at once The geologic time scale begins with the formation of earth about 4.6 billion years ago Pangaea About 245 million years ago the continents where joined in a landmass called Pangaea About 66 million years ago most of the continents had moved away from each other and look like they do now The Origin of Life Modern Ideas Early Ideas Biologists have accepted Spontaneous the concept of generation: the idea BIOGENESIS for more that non-living material can produce than 100 years…but biogenesis doesn’t answer life. the question “How did life Cells only can come begin on earth?”…no one from other cells, so will ever know for sure. this idea was disproved. (biogenesis means cells come from other cells) Modern Ideas Scientists believe two things needed to happen before life could begin 1. Organic molecules (contain carbon) must have formed 2. The organic molecules formed carbohydrates, fats, proteins and nucleic acids The next step proposed by scientists was the molecules would make complex organic compounds called protocells. Protocells: a large ordered structure, enclosed by a membrane that carries out some of life’s activities such as growth and division True Cells The 1st life forms may have been prokaryotes that evolved from a protocell. Because the atmosphere didn’t have much oxygen, it is believed that the 1st organisms were anaerobic (don’t need oxygen) The prokaryotes probably ate the complex molecules that were floating in the ocean (heterotrophs: do not make their own food) Archeabacteria These first cells are thought to be Archeabacteria, these prokaryotes still survive today in the Earth’s harshest environments (volcanoes, deep sea vents, hot springs, salt beds) First True Cells: Prokaryotes Photosynthesizing (make nutrients using energy from the sun) prokaryotes were probably the next organism to evolve. Photosynthesis produces oxygen Because of the extra oxygen, organisms started to become aerobic (using oxygen) Eukaryotes: Endosymbiont Theory Prokaryote ingests some aerobic bacteria. Aerobic bacteria is protected and prokaryote gets energy 2. Over time the aerobes become mitochondria, no longer able to live on their own. 3. This is an animal cell 1. Endosymbiont Theory Some primitive prokaryotes ingested cyanobacteria, which contain photosynthetic pigments 2. The cyanobacteria become chloroplasts and no longer can live on their own 3. This is a plant cell 1.