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The History of Life on Earth Grand Canyon Earth’s Early History • How did the Earth form? – Scientists must explain past events in terms of processes that they can observe. Charles Lyell • Why did the Earth form? – This question is outside of the realm of science. Earth’s Age • Over 4,600,000,000 years old. – First trace of Humans dates to about 1.8 million years ago. • More than 99% of all species that have ever lived have become extinct. Ohio’s Fossil The Fossil Record • Provides evidence about the history of life. • Shows how organisms have changed over time. The Fossil Record • Radioactive Dating – Calculate age of sample based on amount of remaining radioactive isotope it contains based on the isotopes half-life. • Relative Dating – The age of a fossil is determined by comparing its placement with that of fossils in other layers of rock. Earth’s Early Atmosphere Earth’s Early Atmosphere • Probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water. – If you were to travel back in time, after a few short breaths you would no longer exist. Earth’s Atmosphere • Earth was formed 4.6 billion years ago. • Around 3.8 billion years ago changes occurred in Earth’s atmosphere. • Water could remain a liquid on the planet. Earth’s Atmosphere Earth’s Atmosphere • First life found to be around 3.5 billion years old. What type of life? – Single-celled prokaryotic ancestors of modern bacteria. • Little to no oxygen present in Earth’s atmosphere. How is this possible? – Chemosynthesis. Earth’s Atmosphere • 2.2 Billion Years ago • Organisms began producing oxygen, an end product of? • How could this be? – Observation of Oxygen reaction with iron and water. Many rust deposits in rocks dated to this time. Rusty Rocks Earth’s Atmosphere • Organisms churning out Oxygen • What would this do to the atmosphere? – Oxygen increase, methane and hydrogen sulfide concentrations decreased. • What would this do to the microbes on Earth? • Remember we are talking about BILLIONS of years!! The Increase in Oxygen • Poisonous, reactive gas. • Peace early life forms. • Hello life forms equipped to use oxygen in their metabolic pathways. – Respiration The Increase in Oxygen • Stage set for the gradual transition to “modern” life and the gradual transition to modern atmosphere. – Oxygen increase in the atmosphere took over HALF A BILLION YEARS! – Descendants of early anaerobic life forms still exist today. – Use other chemicals such as nitrates and sulfates for metabolism. Origin of Eukaryotic Cells Origin of Eukaryotic Cells • 2 billion years ago. • Internal cell membranes began developing in prokaryotes. • Ancestral eukaryote engulfed prokaryotes. Origin of Eukaryotic Cells • Endosymbiotic theory – Eukaryotes engulfed and formed a symbiotic relationship with prokaryotic organisms. Engulfed prokaryotes are modern day chloroplasts and mitochondria. – Mitochondria and Chloroplasts share many similarities with free-living bacteria. Origin of Eukaryotic Cells Geologic Time Scale Geologic Time Scale Geologic Time Scale Geologic Time Scale Macroevolution • Macro? – Big • Evolution? – Change over time. • Macroevolution – Large scale evolutionary changes that take place over a long period of time.