Download Study Guide

Earth’s History Study Guide
Continental Drift: Earth’s continents were once joined to form one “supercontinent,” Pangaea
Evidence: Matching fossils on coastlines of different continents
Matching rock layers on coastlines of different continents
Tropical plant fossils found in Greenland and Antarctica
Continents “fit” together like puzzle pieces
Plate tectonics: Earth’s lithosphere is broken into plates that move on the asthenosphere. The asthenosphere convection currents, created by heat
from the core, move the plates. Plate boundaries: plates move in relationship to each other in one of three ways:
Divergent: plates move away from each other  
Geologic events earthquakes and volcanic activity
Landforms created: mid-ocean ridges, rift valleys, crust created. Ex: Mid-Atlantic Ridge
Convergent: plates move toward each other   , 3 types based on crust involves
Continental – Continental: folded mountains, earthquakes. Ex: Himalaya Mtns
Continental – Oceanic: coastal volcanic mtns, subduction zone, trench, crust destroyed, earth quakes. Ex: Andes Mtns
Oceanic – Oceanic: Island Arc, subduction zone, trench, crust destroyed, earthquakes. Ex: Aleutian Islands & Japan
Subduction zone: denser/older ocean plate “dives” under the less dense plate. The diving plate is pulled into
the asthenosphere and melted.
Transform: plates slide past each other
Geologic events: earthquakes
Landforms: faults Ex: San Andreas Fault. This boundary DOES NOT create mountains
Uniformitarianism: Earth’s surface is constantly changing. Some changes are slow, some are fast. The same forces that cause these changes in the
past, change earth’s surface now, and will change it in the future.
Law of Original Horzontality: sedimentary rock is formed in horizontal layers.
Superposition: when observing undisturbed sedimentary rock layers, the oldest layer is on the bottom, each layer above it is younger.
Law of Cross Cutting Relationships: disturbances in rock layers are YOUNGER than the layers they cut through

Faults occur AFTER the layers they cut through, they are caused by earthquakes

Intrusions occur AFTER the layers they melt through, they are caused by volcanic activity

Unconformities’ occur AFTER the layers they erode, they are caused by weathering and erosion (usually rivers or glaciers)

Folding occurs AFTER the layers are formed, it is a result of convergent plate movement.
Relative Age: the age of one substance when compared to (relative to ) another (older vs younger, 1st, 2nd, 3rd, etc..)
Absolute Age: using the half life of radioactive material to find the exact age of a rock or fossil. This can only be used on igneous or
metamorphic rocks. A half life is the amount if time it takes HALF a sample to decay from a radioactive parent material into a stable
daughter material. Isotopes of Uranium are usually used to date OLD rock samples (millions or billions of years). Carbon dating (C-14) is
used to date remains of living things that are no older than 50,000 years.
Fossils
Index fossils are used to date rock layers . Index fossils were common, found all over the world, and lived during a brief time. Fossils
can be used to correlate (match) the age of different rock layers.
Fossils are the same age as the rock layers they are found in.
Fossils are NOT found in igneous rock or metamorphic rock because these processes are so hot that remains of organisms are destroyed.
Fossils show how life has changed over time. Life on earth has become more complex and diverse over time.
CLIMATE PROXIES
Ice Cores
Ice cores have evidence of ancient climate. Bubbles in the ice contain ancient air. Scientists analyze the air for CO 2 content and can determine
temperature changes in earth’s history. This information is global. Ice cores also may have ash layers from large volcanic eruptions. The climate and
temperature information from ice cores can be used in current climate models to predict future temperature.
Tree Rings have evidence of local climate. They show rainfall, droughts and fires
Geologic Time Scale is a timeline found in earth’s rock layers of how life evolved on earth.
Increments in the geologic scale are determined by major events (mass extinctions and mass radiations of life).
The first three eons of earth’s time are combined into Pre-Cambrian time. Single celled organisms were the earliest living organisms on earth.
The remaining three eras reflect time life has been on this planet:
Paleozoic Era (ancient life) started with mass radiation of life. Life moved from the sea onto land, the Age of Amphibians. This era ended
with a mass extinction caused by global volcanic activity. More than 90% of the species on the planet became extinct.
Mesozoic Era was the Age of Reptiles. Dinosaurs dominated this era. It ended with the mass extinction of 70% of the species of the planet.
An enormous meteor impact with earth caused the extinction.
Cenozoic Era (current time) is the Age of Mammals.