The origin of living systems is explained by natural processes.

There are several hypotheses about the natural origin of life on Earth, each with supporting scientific evidence 1.D.1

Earth was formed about 4.6 bya Life on Earth emerged about 3.8 bya For the first ¾ of Earth’s history, all organisms were microscopic and unicellular Environment too hostile for life until 3.8 bya Geologic clock compares Earth’s history with 24-hour clock The geological time scale (GTS) is a system of chronological dating that relates geological strata to time, and is used to describe the timing and relationships of events that have occurred during Earth's history. Earliest fossils 3.5 bya, ~18:00:00 Humans = 0:1:15

How is life on Earth documented? Fossil record Relative dating Radiometric dating Fossil = sequence in which fossils appear in the layers of Earth’s surface Relative = order of rock strata Radiometric = decay of radioactive isotopes to determine fossil/rock age

Early conditions of Earth have been simulated in lab experiments Oparin and Haldane “Primordial Soup” theory Early atmosphere was thick with little no oxygen Energy was provided from lightening and UV radiation Simple organic compounds were formed Early Earth had a chemically reducing atmosphere When exposed to energy, monomers were formed These compounds were concentrated at various locations By transformation, more complex polymers (life) developed (

Early conditions of Earth have been simulated in lab experiments (cotd) Miller and Urey tested this hypothesis A variety of amino acids were produced Showed that abiotic synthesis of organic molecules is possible Amino acids = building blocks of proteins Water vapor, methane, ammonia, and hydrogen Cooled to collect condensation in trap

The joining of these monomers produced polymers RNA World Theory states that self-replicating RNA was the first genetic material Some RNAs work as enzymes Some viruses use RNA for heredity RNA required for some fundamental functions of the cell Either within the primordial soup itself, or on biogenic surfaces such as clay, which would act like an enzyme to join monomers together The RNA world hypothesis proposes that life based on ribonucleic acid (RNA) pre-dates the current world of life based on deoxyribonucleic acid (DNA), RNA and proteins. Monomers = molecules that are able to bond into long chains

Be Able To 1.27 Describe a scientific hypothesis about the origin of life on Earth. 1.28 Evaluate scientific questions based on hypotheses about the origin of life on Earth. 1.29 Describe the reasons for revisions of scientific hypotheses of the origin of life on Earth. 1.30 Evaluate scientific hypotheses about the origin of life on Earth. 1.31 Evaluate the accuracy and legitimacy of data to answer scientific questions about the origin of life on Earth.