The History of Earth and Life

Fossils & Ancient Life The study of ancient life using fossil records Paleontologist-A scientist who studies fossils to infer what past life and life forms were like. Fossil Record- Collection of fossils used as information about past life. Provides evidence about the history of life on Earth. Shows how different groups of organisms changed over time. 99% of all species that have ever lived on earth have become extinct.

How Fossils Form The Steps to fossil formation Water carries small rock particles to the bottom of lakes and seas. Dead organisms at the bottom of lakes and seas are buried by the layers of sediment which forms new rock. The weight of the new rock compresses on the lower layers of the new rock and minerals replace all or part of the dead organisms body The preserved remains may later become exposed due to a variety of factors. Most fossils form in sedimentary rock.

Interpreting Fossil Evidence Relative Dating: The age of a fossil is estimated by comparing the fossil to other fossils. Index Fossils- Those fossils used for comparison purposes in relative dating. These fossils are distinctive fossils from specific time periods. This type of fossil dating provides no information about absolute age of the fossil Radioactive Dating: The age of the fossil is calculated based on the amount of remaining radioactive isotopes it contains. Half-life- the length of time it takes for half of the radioactive atoms in a sample to decay. Radioactive dating uses half-lives to determine the age of the fossil.

Geologic Time Scale Scale used to represent evolutionary time. Major changes on fossil records of plants and animals are used to mark where one segment ends and another begins. The basic divisions of the scale are Eras & Periods

Formation of Earth Earth was created approximately 4.6 billion years ago. Clouds and dust condensed into a sphere. Gravity pulled this cosmic debris (matter) together to form a planet. Collisions with other objects ( some as large as planets) produced enough heat to melt the globe. After the earth melted its elements rearranged themselves according to density.

Formation of Earth Cont… 4 Billion years ago Earth cooled. Volcanic eruptions and meteor showers brought the materials to earth to create solid rock. 3.8 Billion years ago the Earth’s surface cooled off enough for water to remain in liquid form. Oceans form. Earths original atmosphere lacked oxygen to support life.

The First Organic Molecules Stanley Miller and Harold Urey conducted laboratory simulations of early earth to explain how early organic molecules emerged from simpler compounds. Energy from an lightning strike may have provided the electrical spark needed to combine atoms of the atmosphere and form molecules necessary for life on Earth to exist. Earth can now produce organic molecules like carbohydrates, proteins, lipids and amino acids.

The Puzzle of Life’s Origin Formation of Microspheres Under certain conditions large macromolecules can form tiny bubbles called proteinoid microspheres, which can exhibit the properties of cells. Some scientists believe these microspheres took on more and more of the cells characteristics and eventually became what we know of as cells. Evolution of RNA and DNA Neither DNA or RNA can exist without each other. So which can first?????? Scientists think RNA existed first and gave way to DNA However, many questions still exist about the evolution of DNA and RNA.

Free Oxygen Microfossils- fossils of microscope organisms found in rock 3.5 million years ago. These organisms were single celled prokaryotic organisms known as anaerobes(organisms that lived without oxygen). Anaerobes today exist in airless environments. Photosynthetic bacteria evolved and began to put oxygen into the atmosphere. Gives way to aerobes (organisms that need oxygen). Many anaerobes died because oxygen was toxic to them. Ozone layer now forms.

Origin of Eukaryotic Cells Prokaryotic cells (those cells that don’t have a nucleus) gave way to Eukaryotic cells (those cells that do have a nucleus). Endosymbiotic Theory- Eukaryotic cells formed from a symbiosis among several different prokaryotic organisms. Sometime after eukaryotic cells emerged they began to reproduce sexually which allowed evolution to speed up.

Evolution of Multi-cellular Life Eras: Cenozoic Mesozoic Paleozoic Precambrian Periods: Quaternary Tertiary Cretaceous Jurassic Triassic Permian Carboniferous Devonian Silurian Ordovician Cambrian Vendian

Patterns of Evolution Macroevolution: The large scale evolutionary patterns and processes that occur over long periods of time. Extinction: The elimination of the existence of a species. Natural selection has caused 99% of all species to go extinct. Mass extinction- the extinction of an entire ecosystem. Serious large event that causes the mass extinction. Dinosaurs wiped out this way. Clears the way for the evolution of modern species like mammal and birds.

Patterns of Evolution Cont…. Adaptive Radiation: Process by which a single species or group of species evolves into several different forms that live in different ways. Leads to rapid growth in diversity Convergent Evolution: Process by which unrelated organisms independently evolve similarities when adapting to similar environments.

Patterns of Evolution Cont…. Co-evolution: The process by which two species evolve in response to change in each other over time. EX: Plants and the insects that pollinate them. Punctuated Equilibrium: Describes pattern of long stable periods interrupted by brief periods of more rapid change. Gradualism: Slow, steady, gradual change.

Developmental Genes and Body Plans Small changes in the activity of control genes that can many other genes and cause larger changes in adult animals. Changes caused by changes in activation genes. EX: Many pairs of wings on ancient insects but only a single pair of wings on modern insects.