Earth Formation & Early History Fossils – Remains of living things that died long ago. Usually found in sedimentary rock. Older rocks contain fossils that are much simpler than organisms of today.

Types of Fossils: Trace Fossils – Show how ancient organisms behaved. Examples are burrows, footprints, and even dung. Index Fossils – Widely distributed throughout the world for a brief amount of time. Useful because they tell you how old the rock is in which they are found.

Change Over Time: Evolution – Gradual change in living things that happens over a long time. Extinct – Organisms that have died out.

Relative Age of Rocks: Lower layers are older than upper layers. Layers don’t always line up neatly Extrusion – New rock that forms on top of sedimentary rock Law of Superposition – In layers of horizontal sedimentary rock, the oldest layers are on the bottom. Younger layers are above older layers.

Relative Age of Rocks (cont.): Intrusion – New rock that forms inside sedimentary rock Fault – A break in rock where rocks can move Scientists use index fossils to match rock layers in different places.

Radioactive Dating: The process of dating geologic materials based on the nuclear decay of radioactive isotopes. Radioactive decay – When an element breaks down, it changes into another element. Half-life – The time it takes for half of a sample to break down. Radioactive dating works well for igneous rocks, but not sedimentary.

The Planet Forms: Rocks from the moon are known to be 4.6 billion years old. Scientists think the Earth and moon are the same age. Also meteorites collected date to 4.6 billion years. (formed same time Earth did -- leftovers!) Collision-Ring Theory

Early Earth: Did Earth start as a ball of dust, rock, and ice? Why so hot then? Meteor strikes (KE to Thermal E) How did it form? Gravity? Where did 1st atmosphere come from? Solar flare probably blew away the Earth’s first atmosphere of Hydrogen & Helium

Early Earth: Early atmosphere (2nd technically) of carbon dioxide, nitrogen, and water vapor. Where did it come from? Outgassing from volcanic processes. Too hot for liquid water As organisms began using energy from the sun to make food, called photosynthesis, they used carbon dioxide and gave off oxygen.

Earliest earth forms lived in water and were very simple. Early Earth: Earliest earth forms lived in water and were very simple. New evidence suggest water was present as long as 4.28 billion years ago. About 3 billion years ago, organisms were able to use the sun to make their own food. This helped cool the planet and make other life possible. How?

Early Earth: Meteor strikes also help bring water to the planet Once oxygen was in the atmosphere, ozone started to form This helped filter out harmful UV radiation and help cool the planet This caused water vapor from the atmosphere to condense and add to the oceans

Geologic Time Scale: The record of Earth’s history documenting geologic events and life forms. 4.6 Billion years ago to present Eras are large chunks of time (several hundred million years to billions of years long). Each era divided into smaller blocks called periods.

Eras of Earth’s history: Precambrian Era – longest era from 4.6 bya to 544 mya. Bacteria formed about 3.5 bya and other soft-bodied multi-cellular organisms toward the end of the era. As the Earth cooled, shallow seas covered the planet as early as 4 bya. Earth’s crust cools and hardens

Paleozoic Era 544 mya to 245 mya This era has six periods. Cambrian period is the first of these six All animals in the Cambrian were invertebrates and lived in shallow seas Near the end of the Paleozoic (about 260 mya) supercontinent Pangaea forms.

Mesozoic Era From 245 mya to 66 mya Era has three periods Triassic – First dinosaurs (reptiles) and mammals appeared Jurassic – Dinosaurs were the main land animals. Birds also appeared. Cretaceous – Plants with flowers Pangaea begins to break apart.

Cenozoic Era 66 mya to present time Called the “Age of mammals” Rocky Mountains and Himalayas form during the Tertiary period. (66 mya- 1.8 mya) Quaternary period from 1.8 mya to present. Mammals, flowering plants, and insects main life forms in this period.

Mass Extinctions: Scientist think mass extinctions occur at the end of each Era. There are 3 major reasons for mass extinctions: (They all cause major climate change!) Impacts from space Volcanic eruptions Natural changes in Earth’s revolution.