1. The History of Life on Earth Life Science

2. Evidence of the Past Fossils provide clues about to Earth’s past. They are traces or imprints of living things such as animals, plants, bacteria, and fungi.

3. The Age of Fossils The age of fossils are determined by scientist in two major ways. relative dating: any method that is used to ESTIMATE the age of rocks and fossils absolute dating: the age of fossils and rocks are determined more precisely. In some cases the atoms of an object are examined

4. The Geologic Time Scale The calendar that scientist use to outline the history on Earth is called the geologic time scale.

5. Divisions in the Geologic Time Scale Paleontologists have divided the geologic time scale into large blocks of time. The divisions known as ERAS are characterized by the type of organism that dominated Earth at the time. The geologic time scale is also divided into periods and time.

6. Divisions in the Geologic Time Scale

7. Mass Extinctions Divisions of the geologic time scale mark times when rapid changes happened on Earth. Some of the changes are a part of theories that scientist have come up with regarding the mass extinction of dinosaurs.

8. Mass Extinctions

9. The Changing Earth Pangaea is a theory proposed by Alfred Wegener that the Earth was once a large landmass that slowly drifted apart.

10. The Changing Earth Conditions on the Earth change, organisms may become extinct. If they do not, they adapt to the new environment, just like the Continental Drift Theory. Conditions on Earth have changed many times in history, and life has changed too.

11. Eras of the Geologic Time Scale The oldest part of the geologic time scale is the Precambrian time. This era begins when the Earth was formed 4.6 billion years ago to about 542 million years ago. Scientist think that the Earth developed from simple chemicals in the oceans, and in the atmosphere.

12. Eras of the Geologic Time Scale The Paleozoic era began about 542 million years ago and ended about 251 million years ago. Fishes, the earliest animals with backbones, appeared during this era and sharks become abundant.

13. Eras of the Geologic Time Scale Life on land also appeared during this era, which lasted for 300 million years. By the end of the era, forests of giant ferns, club mosses, horsetails, and conifers covered much of Earth. The largest mass extinction known took place at the end of the Paleozoic era.

14. Eras of the Geologic Time Scale The Mesozoic era began about 251 million years ago and lasted about 185.5 million years Dinosaurs are the most well known reptiles that evolved during the Mesozoic era. They dominated Earth for about 125 million years. Birds and flowering plants also appeared during this time.

15. Eras of the Geologic Time Scale

16. Humans and Other Primates Humans are classified as primates. Primates are a group of mammals that includes humans, apes, monkeys, and lemurs. Some characteristics of these primates include larger brains, and had both eyes located at the front of the head.

17. Humans and Other Primates The chimpanzee, a type of ape, is the closest living relative of humans. This does not mean that humans come from chimpanzees.

18. Humans and Other Primates Humans are in a family which is separate from other primates. This family is called hominids. Bipedalism is the only thing that separates humans from all other primates. Bipedalism means “mostly walking upright on two feet”

19. Humans and Other Primates Early hominids are classified as australopithecines. They were similar to apes but had larger brains, used stone tools and walked on two legs. Fossil evidence of these hominids were found in Africa.

20. Humans and Other Primates About 2.4 million years ago, a more advanced hominid appeared. They were members of the group homo. No one knows what these early hominids looked like but based on fossil evidence we know that they grew as tall as common day humans.

21. Humans and Other Primates Recent hominids are the neanderthals who lived in Europe and western Asia. They hunted large animals, made fires, and wore clothing. About 30,000 years ago they disappeared and no one knows why.

22. Humans and Other Primates Modern humans are classified as Homo sapiens

23. Humans and Other Primates Homo sapiens existed in Africa 100,000 to 160,000 years ago. Homo sapiens had a smaller, flatter face, and a skull more rounded than the Neanderthals. Early humans produced sculptures, carvings, paintings, and clothing.