Chapter Eight: The History of Life on Earth
Section One: Evidence of the Past
Fossil- the trace or remains of an organism that lived long ago, most commonly preserved in sedimentary rock
Relative dating- any method of determining whether an event or object is older or younger than other events or objects
Absolute dating- any method of measuring the age of an object or event in years
Geologic Time Scale- the standard method used to divide the Earth's long natural history into manageable parts
Extinct- describes a species that has died out completely
Plate Tectonics- the theory that explains how large pieces of the Earth's outermost layer called tectonic plates, move and change shape
Chapter Eight, Section One: Summary
Fossil of a winged creature.
Section one was about Earth's past. When organisms die it is buried in sediment. The sediment is the pressed together to form sedimentary rock which the fossil is in. Estimating fossil ages is relative dating. Finding the exact age is absolute dating. You can find the absolute date of something by measuring the ratio of stable to unstable atoms. The geologic time scale is dived into eras. The eras are then divided into periods.The earliest time of the geologic scale is not an era. When an entire species dies, they never return. When many species die out, that is a mass extinction. Extreme climate changes or forces within Earth could have caused a mass extinction. Earth was once a large piece of land. Scientists call it Pangaea. The theory of plate tectonics is the continents and oceans sit on plates. The plates are slowly moving, carrying the continents and oceans with them. Slow changes on Earth give organisms time to adapt. Faster changes, organisms don't have time to adapt, so they become extinct.
Section Two: Eras of the Geologic Time Scale
Precambrian Time- the period in the geologic time scale from the formation of the Earth to the beginning of the Paleozoic era, from about 4.6 billion to 542 million years ago
Paleozoic era- the geologic era that followed Precambrian time and that lasted from 542 million to 251 million years ago
Mesozoic era- the geologic era that lasted from 251 million to 65.5 million years ago; also called the Age of Reptiles
Cenozoic era- the most recent geologic era, beginning 65 million years ago; also called the Age of Mammals
Chapter Eight, Section Two: Summary
The Paleozoic era and its periods.
Section two was about the eras. Life began from simple chemicals. The chemicals reacted and caused prokaryotes to form. Cyanobacteria photosynthesized and released oxygen in the air. The oxygen caused the ozone to form. The prokaryotes then evolved into eukaryotes. The Paleozoic era had all plants except for plants with flowers. Most of the organisms in the era lived in the oceans The near end of the era reptiles and winged insects. The end of the Paleozoic era was the largest mass extinction. The Mesozoic era was dominated by dinosaurs. The conifers also appeared, creating large forests. Dinosaurs became extinct. The theory is a meteorite hit Earth sending dust in the air blocking the sun. The plants died, causing the plant eating animals to die, causing the meat eating animals to die. Some organisms did survive though. We are living in the Cenozoic era. This era was dominated by mammals. The early mammals were small and lived in forests. The later mammals were bigger and had long legs, sharp teeth, and larger brains. The climate changed many times.
Section Three: Humans and Other Primates
Primate- a type of mammal characterized by opposable thumbs and binocular vision
Hominid- a type of primate characterized by bipedalism, relatively long lower limbs, and lack of a tail
Homo Sapiens- the species of hominids that includes modern humans and thier closest ancestors and that first appeared 100,000 to 160,000 years ago
Chapter Eight, Section Three: Summary
Human skull evolution from primates.
Section three was about humans. Chimpanzees are the closest living relative of the humans. Humans are hominids. The major characteristic that separates them from other primates is bipedalism. Bipedalism is mainly walking on two feet. Early hominids have been found in Africa. Early hominids are apart of a group called australopithecines. They were similar to apes, but they had larger brains. Some australopithecines had thin bodies and human-like teeth. Some had larger bodies and small brains. New hominids were apart of a group called Homo. Recent hominids are Neanderthals and early humans. Neanderthals made fires, wore clothing, cared for the elderly, and buried the dead ceremoniously. They went extinct, but no one knows why. Modern humans are Homo Sapiens. Humans are the only known hominid that still exists.
Now that you know about Earth's history, here is a song about the eras.