Ch 12: The History of Life

The geologic time scale divides Earth’s history based on major past events.

Geologic Time Scale Is a representation of the history of the Earth Organizes Earth’s history by major changes or events that have occurred, using evidence from the fossil and geologic records.

Organization of the Geologic Time Scale Divided into a series of units based on the order in which different groups of rocks and fossils were formed.

3 basic units: 1.Eras- – last tens to hundreds of millions of years – consist of two or more periods – three eras: Cenozoic, Mesozoic, Paleozoic 2.Periods- – most commonly used units of time on the scale – lasting tens of millions of years – Each period is associated with a particular type of rock system. 3.Epochs- – smallest units of geologic time – last several million years

Multicellular life evolved in distinct phases.

Paleozoic Era Multicellular organisms first appeared during the Paleozoic era. The era began 544 million years ago and ended 248 million years ago. The Cambrian explosion led to a huge diversity of animal species.

Mesozoic era known as the Age of Reptiles. It began 248 million years ago and ended 65 million years ago. Dinosaurs, birds, flowering plants, and first mammals appeared during this time.

Cenozoic era First appearance of mammals The Cenozoic era began 65 million years ago and continues today. Placental mammals and monotremes (lay eggs) evolved and diversified. Anatomically modern humans appeared late in the era. – This is YOU!!

Primates Primates are mammals with flexible hands and feet, forward-looking eyes and enlarged brains. Also have arms that can rotate in a circle around their shoulder joint, as well as thumbs that can move against their fingers. – Opposable thumbs Include: – Lemurs, monkeys, apes and humans Primates share physical traits and molecular similarities.

Evolutionary Relationships of Primates Primates are divided into 2 groups: – Anthropoids – Prosimians Anthropoids are divided into: – Hominoids – Monkeys Hominoids are divided into: – Lesser apes (gibbons) – Great apes (orangutans, chimpanzees, and gorillas) – Hominids (include humans)

Hominid Species Classified into 2 groups: – genus Australopithecus – genus Homo Australopithecus afarensis – Lived 3-4 million yrs ago in Africa – Smaller brain, humanlike limbs Homo habilis – Lived million yrs ago in modern day Kenya and Tanzania – Earliest known hominid to make stone tools – Brain was larger and shape was more similar to that of a modern human

Hominid Species Homo neanderthalensis – Lived 200,000 to 300,000 yrs ago in Europe and Middle East Homo sapiens – Includes modern humans – First appeared in Ethiopia around 100,000 yrs ago ( according to fossils found there) – Different features from modern humans Proof that the species did not stop evolving

Examples of Hominid Skulls Australopithecus afarensis Homo habilisHomo neanderthalensis Homo sapiens