Chapter 8 Science

Because scientists think ____________ and ____________ formed from the same event, they have used the ages of meteorites found on Earth's surface to determine Earth's age.

asteroids and planets

There is extensive fossil evidence that shows the evolution of human ancestors, even _________ the most recent ice age.

before

Most of the rock that makes up Earth's crust formed during the _______________ ______ , which is why we have so much more information about this eon and why it takes up more space on the model. Because of ________________ and ___________ ___________, there are few rocks left that formed during Earth's first three eons.

current eon , weathering and plate tectonics

The absence of the ______________ allowed land and water mammals to thrive and diversify. The first primates appear ___ million years ago

dinosaurs, 55

mass extinctions occur when a large number of species go __________ over a relatively short period of time.

extinct

The atmosphere and oceans formed 4.4 billion years ago from _________ and ________ ________ released by volcanoes.

gases and water vapor

The____________ _________ __________ is a model of Earth's history divided into the main units of geologic time from longest to shortest, and includes eons, eras, periods, and epochs. Ga is for billions of years, Ma is for millions of years, and ka is for thousands of years.

geologic time scale

Scientists organize Earth's 4.6-billion- year history on a ___________ _______ __________. __________ ____________ reveal major events in Earth's history.

geologic time scale, Rock strata

According to the _________ _____________ ____________, a Mars-sized planet struck Earth, causing a large part of Earth's mantle to be ejected into its orbit, where the debris came together to form the moon.

giant impact hypothesis

What formed after the Permian Extinction?

giant reptiles and flying insects which evolved into dinosaurs

A ____________ ___________ is a time of even cooler temperatures, when large ice sheets advance from the poles toward the equator.

glacial period

Earth is in an ___ ____ that began 2.6 million years ago.

ice age

Explanation of nebular hypothesis

According to this hypothesis, a cloud of gas and dust, called a nebula, began to contract about 4.6 billion years ago. The nebula began to take the shape of a spinning disc. During this time, collisions between dust particles and the force of gravity caused some of the matter in the nebula to clump together. As the clumps orbited the center of the nebula, they collected more dust particles in their paths. As the clumps grew larger, their gravitational pull became stronger, and they attracted even more particles until eventually, they formed the sun and planets, as shown in Figure 2. Some debris remained, however, in the form of asteroids. Because scientists think asteroids and planets formed from the same event, they have used the ages of meteorites found on Earth's surface to determine Earth's age.

When the North and South Poles are covered by ice caps, as they are now, Earth is said to be in an ____ ____. An ice age is a long period of globally cooler temperatures in which permanent ice exists at the poles.

ice age

How did the atmosphere and hydrospheres form?

After Earth's crust formed, volcanoes began to erupt and release gases such as carbon dioxide and water vapor. Over millions of years, these gases formed Earth's early atmosphere. Figure 3 shows that as Earth began to cool, the water vapor in Earth's new atmosphere condensed to form liquid droplets, and it began to rain. Eventually, enormous amounts of water accumulated in deep basins and formed the oceans.

An _________________ period is a time of warmer temperatures, when ice sheets begin to melt and retreat toward the poles.

interglacial

In the same way that you might record memorable events in order in your life, scientists organize geologic time by ____________ __________ that shaped Earth's history.

major events

What causes this?

mantle convection, tectonic plate movement, sea floor spreading, continental convergence, mountain ranges

The first ancient relatives of all major groups of modern animals evolved in the oceans during this relatively short amount of geologic time—about 11 million years. this period of time is known as the _____________ ______________.

Cambrian Explosion

Beginning about 390 million years ago, Pangaea formed, volcanic eruptions may have caused two _______ ______________, and dinosaurs dominated.

mass extinctions ,

Scientists _____________ use to date Earth and the solar system

meteorites

Scientists have developed hypotheses about how the solar system, Earth's layers, and the _______ formed.

moon

Most scientists agree that the ________________ hypothesis is the most likely explanation for the formation of the solar system.

nebular

the first _____________ (a group of mammals that includes monkeys, apes, and humans) appeared early in this era, about 55 million years ago.

primates

The principle of lateral continuity states that sedimentary layers can extend laterally in all directions until they reach an obstacle. That is why the Dakota sandstone and Kaibab limestone layers are found in more than one canyon. Comparing sequences of rock strata from different locations helps to provide a more complete picture of Earth's history.

refer to picture

Around 200 million years ago, Pangaea began splitting up into separate continents, causing dinosaur populations to become ____________________.

separated

Even though mostly ______________ mammals lived at the same time as dinosaurs, once dinosaurs were gone, ___________ mammals began to evolve, thrive, and diversify. For the next 66 million years, mammals continued to increase in type and number, and many increased in size.

smaller, larger,

Ice ages shape Earth's ______________.

surface

Give an example of how important Ice ages have played in shaping Earth's surface.

the Great Lakes formed when large and heavy ice sheets advanced across the land surface. The weight of the ice caused the crust to sink low enough that deep basins formed. Once the interglacial period began and the ice melted, water filled up the basins to form the Great Lakes.

_________________ is the rapid appearance, or evolution, of new species.

Diversification

Earth's early atmosphere did not contain any oxygen. The organisms that lived about 3.5 billion years ago did not need oxygen. So where did the oxygen in today's atmosphere come from?

Stromatolites are fossilized colonies of single-celled organisms called cyanobacteria, which could live without oxygen. Cyanobacteria were the first organisms to carry out photosynthesis, which releases oxygen.

Summary

Summary

How did the dinosaurs become extinct?

The Age of the Dinosaurs came to a sudden end 66 million years ago in the Cretaceous Mass Extinction. Evidence shows that a large asteroid struck Earth in what is now known as Chicxulub on the Yucatán Peninsula in modern-day Mexico at the same time dinosaurs went extinct. Scientists hypothesize that the impact of the asteroid released a cloud of dust into the atmosphere, which blocked most of the sun's energy. This would have killed off plants and other food the dinosaurs needed to survive, and would have caused a global decrease in temperature.

Where and what is the Burgess Shale and why is it so important?

The Burgess Shale is an important resource for scientists because it preserved so many different types of organisms, even those without hard shells.

What caused the Permian Mass Extinction?

The most likely explanation is that massive, long-lasting volcanic eruptions changed the climate. The largest volcanic eruptions in Earth's history took place at this time in what is now Siberia, Russia. Scientists hypothesize the eruptions released gases into the air that caused rapid global warming. The eruptions lasted more than one million years and occurred at the same time as the mass extinction.

Explain the formation of the Earth's core

The newly formed Earth was so hot that it was almost completely molten, or liquid, rock. Scientists think that originally all of Earth had the same composition, from its surface all the way to the center of the planet. However, this was about to change. Because it was molten, the rock could move around freely. Heavy elements, such as iron and nickel, began to sink to Earth's center. At the same time, lighter elements, such as silicon and aluminum, rose toward the surface. Look again at Figure 2. By about 4.5 billion years ago, Earth had formed the layers called the core, mantle, and crust.

True or false. Many other types animals evolved, including birds and small mammals. Huge ferns and forests started growing and provided a food source for the dinosaurs and other animals. Later, the first flowering plants appeared.

True

The Great Rift Valley in eastern Africa began to form as two parts of the African Plate pulled away from each other. Scientists believe that one day, the African Plate will split along the Great Rift Valley to form ______ _____________ plates.

2 smaller

Fossil evidence shows that modern humans appeared more than _____________ years ago.

200,000

The Age of the Dinosaurs began about ____ million years ago. Dinosaurs dominated the land for the next 164 million years.

230

the Age of the Dinosaurs lasted from ______ to ______ million years ago

230 to 164

Pangaea began forming in the middle of the most recent eon, about ___ __________ years ago, when the continents started coming together

390 million

How old is Earth?

4.6 billion years old

Scientists determined that there have been ________ mass extinctions in Earth's history. Geologists can tell when events like mass extinctions occurred by the disappearance of certain __________ from the rock strata.

5, fossils

The Canyon Diablo meteorite in the photo was used as evidence for Earth's age. It was part of an asteroid that struck Earth about ____________ years ago, its impact forming Barringer Crater in Arizona. Using _____________ _________, scientists found that the meteorite was about 4.6 billion years old—the ______ _ ____ ________ ___________.

50,000, absolute dating, age of the solar system

How did the atmosphere evolve to be 21% oxygen?

For over a billion years, the oxygen released by cyanobacteria was absorbed by ocean water and sediment on the seafloor. When no more oxygen could be absorbed it began to accumulate in the atmosphere. It took another 2 billion years for oxygen in the atmosphere to reach its present level of 21 percent.

_____________ provide evidence of the first life forms.

Fossils

After the breakup of Pangaea, India began moving northward relatively rapidly. By about 50 million years ago, it collided with Eurasia and began forming the _________________.

Himalayas

Because the iron core formed relatively quickly and under extreme conditions, scientists refer to this event as the ________ ____________________.

Iron Catastrophe

_________________ provide the best direct evidence for the age of Earth and the solar system.

Meteorites

What is the tallest mountain on Earth in this mountain range?

Mount Everest, continues to grow 1 cm taller every year

By about 400,000 years ago, _______________ appeared. The first modern humans appeared more than _______________ years a

Neanderthals, 200,000

The new supercontinent covered about one-third of Earth's surface. What was this called?

Pangaea

While Pangaea was forming, the most severe mass extinction in Earth's history occurred. What was it called?

Permian Mass Extinction