The History of Life Biology

Early History of Earth Earth’s Atmosphere was probably composed of CO2 and Nitrogen. But with the continuous eruptions of the volcanoes led to the formation of the atmosphere. After it cooled about 4.4 billions ago, water condensed, and precipitation was released and the oceans were formed. Scientist believe that this occurred about 3.9 and 3.4 billion years ago.

Fossils-Clues from the past Earth holds a large diverse group of life. This is a small fraction of the species that ever existed. About 95% of the species that have existed are extinct. Fossils is one form that scientist use to study ancient species. A fossil is evidence of an organism that lived long ago.

Types of Fossil Trace fossils- Indirect evidence, example a footprint, a trail or burrow. Casts- when minerals in rocks fill a space left by decayed organisms. Molds- when an organism is buried in sediments and then decays and leaves an empty space. Petrified- minerals replace hard parts of the organism. Amber/Frozen- entire organism is trapped.

Relative Dating A technique used to determine the age of fossils. If rock layers are left undisturbed, the scientist is able to give the relative age of fossils. They do this by determining that older rocks are found in the bottom of layers compared to those found on top. Not very accurate because of natural changes that occur on Earth.

Radioactive dating This technique is used to find the specific age of rocks. Fossils and sedimentary rocks cannot be radiometrically dated. Most dates are for volcanic and other igneous rocks, or metamorphic rocks closely related to sedimentary rocks. A method for determining the age of an object based on the concentration of a particular radioactive isotope contained within it. For inorganic materials, such as rocks containing the radioactive isotope rubidium, the amount of the isotope in the object is compared to the amount of the isotope's decay products (in this case strontium). The object's approximate age can then be figured out using the known rate of decay of the isotope. For organic materials, the comparison is between the current ratio of a radioactive isotope to a stable isotope of the same element and the known ratio of the two isotopes in living organisms. Radiocarbon dating is one such type of radiometric dating.

Diversity of Precambrian Some rocks date back to about 3.4 billion years ago. 87% of the Earth’s history is spent in the Precambrian Time. Type of life that existed then were Stromatolites. Organisms similar to modern day cyanobacteria. Cyanobacteria is a photosynthetic water organism. These organism were prokaryotic. Unicellular organisms with no membrane bound orgnalles. Eukaryotic organisms appeared about 2.1 billion years ago. Multicellular organisms appeared about the end of Precambrian ( 543 million years ago)

Diversity of the Paleozoic Lasted until about 248 million years ago. Earth had a larger diversity of life. Earliest part of the Paleozoic is called Cambrian. The oceans contained many organisms like worms, sea stars and arthropods. First half of Paleozoic had fish and animals with back bone and ferns. Mid Paleozoic four legged animals appeared. Last half reptiles appeared and flourish on land. The end of the Paleozoic is marked as the largest mass extinction of species. 90% marine animals and 70% land species dissappeared.

Life in the Mesozoic Began 248 million years ago. Many geological and organism changes occurred during this Era. Divided into 3 Periods Triassic- oldest period mammals appeared. Thought to small and mouselike. Jurassic- 206 million years ago. Modern birds evolved from one group of dinosaurs. Cretaceous- Last period, began 144 million years ago. Mass extinction of dinosaurs but many new types of mammals and plants appeared.

Changes during the Mesozoic Geological events changed the Earth’s land. Continental Drift occurred and changed where animals lived. Theory of Plate Tectonics

The Cenozoic Era Began 65 million years ago. Tertiary-Mammals began to flourish along with a group of animals somewhat related to you. The primate group first appeared about 65 million years ago. Quaternary-The human species appeared about 200,000 years ago.

Mass Extinctions Extinction- death of all members of a species Mass extinction- episode during which large numbers of species become extinct Ordovician period 440 million years ago was the first mass extinction Second mass extinction= 360 million years Third mass extinction = 245 million years ago Most devastating loosing 96% of all species Fourth mass extinction= 200 million years ago Fifth mass extinction = 65 million years ago- dinosaurs

The Origin of Life Spontaneous Generation: the idea that nonliving material can produce life.

FRANCESCO REDI’S EXPERIMENT 1668 REDI’S EXPERIMENT SHOWED THAT FLIES WERE THE PRODUCT OF BIOGENESIS. HE DEMONSTRATED THAT FLIES DIDN’T ARISE FROM ROTTING MEAT, BUT WERE THE OFFSPRING OF FLIES DRAWN TO THE ROTTING MEAT.

Louis Pasteur Disproved the spontaneous generation of microorganisms. After disproving it, the idea of biogenesis was accepted. Biogenesis- living can only come from other living things.

Alexander Oparin Hypothesized that life formed in the oceans. Through energy from the sun, lightning, and Earth’s heat triggered chemical reactions to form small organic molecules from substances in the air. Then the rain formed this primordial soup.

Miller and Urey Tested Oparin’s Hypothesis by simulating Earth’s Early atmosphere ( ammonia, water vapor, methane, and hydrogen gases. They sent electric currents to simulate lightning and this created several kinds of amino acids, sugars, and small organic molecules.

Sidney Fox and The formation of Protocells This occurred when these amino acids were heated and proteins formed. American Biochemist Sydney Fox tested this hypothesis by heating solutions of amino acids and forming protocells. A protocell is a structure enclosed in a membrane that carries out some life activities, such as growth and division.

The Evolution of Cells Even though the geological scale shows prokaryotes as the first life to exist. They were probably anaerobic. They were considered to be heterotrophs because the ate the molecules formed in oceans. Through this process autotrophs probably formed. These were archeabacteria.

The Evolution of Cells Eventually photosynthesizing organisms formed. They were the ones that released oxygen into the atmosphere. This eventually formed the ozone layer that gave protection from UV rays. This enabled the formation of complex organisms. The Endosymbiont Theory: Complex Eukaryotes formed from prokaryotic organisms. This occurred by ancient prokaryotic organisms having close relationship with simple eukaryotes.

Cellular Life Begins Fossil – preserved or mineralized remains (bone, tooth, or shell) or imprint of an organism that lived long ago Prokaryotes- single celled organisms 2.5 billion years old. Lack internal membrane bound organelles

Dr. Lynn Margulis 1966 Endosymbiosis Mitochondria- descendants of symbiotic, aerobic eubacteria Chloroplasts are descendants of symbiotic, photosynthetic eubacteria

Mitochondria and Chloroplasts Both have circular DNA similar to bacteria chromosomes Both have genes that are different from the host cell Both have ribosomes that are similar to bacterial ribosomes Reproduce by fission Replication is independent of the host cell cycle