History of Life on Earth

• Evolution - The process of change over time.
• Evolution - a change in the genetic makeup (and often, the heritable features) of a population over time.
• Evolution as descent with modification - a phrase Darwin used in proposing that Earth’s many species are descendants of ancestral species that were different from the present-day species.
• 4.5 billion years old - age of Earth.
• 3.5 billion years ago - the first living organisms (similar to bacteria) have appeared on Earth.
• Geologic Time Scale - record of the life forms and geological events in Earth’s history.
• Relative dating - position of fossils in the sedimentary rocks.
• Radioactive dating - was used to determine the absolute divisions in the time scale.
• Relative dating - Method used to determine the age of the rocks by comparing them with the rocks on the outer layer.

  Top (upper) - younger

  Bottom – older

• Radiometric dating - determines the age of rocks using the decay of radioactive isotopes.
• A radionuclide is a nuclide that has excess numbers of either neutrons or protons, giving it excess nuclear energy, and making it unstable.
• The Earth’s history is divided into: Eons, Eras, Periods and Epochs.
• Epochs - less than 10 million years.
• Periods - lasting for 10 million years.
• Eras - which last for   hundreds of millions of years.
• Eons - which last for billions of years.
• Precambrian - covers approximately 88% of the Earth’s history.
• Archaean - first life on Earth.
• Ediacaran - oldest eukaryotic cell; soft boiled invertebrate animals.
• Proterozoic - formation of supercontinent Rodinia.
• Paleozoic Era - also known as Old Life.
• Paleozoic Era is divided into 6 periods: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian.
• Cambrian - sudden increase in diversity of life forms, including the first fish, and many animals diversify due to the Cambrian Explosion.
• Ordovician - first plants occurred; fungi, plants, and animals colonize the land.
• Silurian - first vascular plant appeared.
• Carboniferous - origin of reptiles; first seed plants appear; amphibians are dominant.
• Permian - reptiles diversify; the largest mass extinction in history also occurred, wiping out approximately 90% of all marine animal species and 70% of land animals.
• Mesozoic Era - also called Middle Life.
• Mesozoic Era is divided into 3 periods: Triassic, Jurassic, and Cretaceous.
• Triassic - origin of mammals; dinosaurs evolve and gymnosperms dominate the land.
• Jurassic - dinosaurs are abundant'; first bird appeared; gymnosperms dominate.
• Cretaceous - angiosperms diversify and dinosaurs became extinct at the end of this period.
• Cenozoic Era - also known as Recent Life.
• Cenozoic Era is divided into 3 periods: Paleogene, Neogene, and Quaternary.
• Paleogene Period is divided into 3 epochs: Paleocene, Eocene, and Oligocene.
• Neogene Period is divided into 2 epochs: Miocene and Pliocene.
• Quaternary Period is divided into 2 epochs: Pleistocene and Holocene.
• Paleozoic Era - supercontinent Pangea was formed.
• Paleocene Epoch - mammals, birds, and pollinating insect diversify.
• Eocene Epoch - angiosperms dominate and mammals diversify.