Chapter 17
Shooting stars average about ______ diameter in size.
1 mm
There are ______ meteoroids that enter Earth's atmosphere daily.
100,000 million or more
The vast majority of the asteroids in the asteroid belt have diameters between ______ and ______ kilometers.
1; 30
The energy released during an impact event leaves a crater about ______ times larger than the diameter of the space object.
20
Choose the correct size and velocity of the asteroid that created the Chicxulub crater.
6 miles 47,000 mph
Whereas ______ asteroids have orbits that pass near Earth, ______ asteroids have orbits that intersect Earth's orbit.
Amor; Apollo
What hypothesis did Luis Alvarez propose to explain the iridium-rich clay layer located at the Cretaceous-Teritary boundary?
An iridium-rich asteroid struck Earth.
The continent of is a great place to hunt for meteorites because ice flows tend to concentrate them in specific areas, making it much easier to discover and collect them.
Antarctica
The three largest asteroids, ______, ______, and ______, make up about one-half the combined total mass of all asteroids in the asteroid belt.
Ceres; Vesta; Pallas
An asteroid about 10 km in diameter struck Earth near the modern-day Yucatan Peninsula with a velocity of about 21 km/sec, creating the ______ crater.
Chicxulub
Which of the following statements best describes the shape of most comet's orbits?
Comets have a very eccentric orbit that takes them near the Sun at perihelion and then out beyond the outermost planets at aphelion.
Smaller, house-sized objects pass very close to Earth many times each day. However, these objects are not a threat to human civilization because ______.
Earth's atmosphere acts as a defense system, causing these objects to break up and explode before they become a threat on the ground
True or false: The vast size of our Solar System makes it almost impossible for a large, civilization-threating asteroid or comet to collide with Earth.
False
Returning to the inner Solar System approximately every 76 years, comet is one of the most well-known periodic comets. It is named after the scientist who first calculated its orbit in 1682.
Halley's
The Tunguska event did not leave an impact crater. What does that suggest about the identity of the impactor?
It was likely the fragment of a comet or a large stony meteorite.
Which of the following is not a line of evidence used to support the Alvarez hypothesis for the origins of the Cretaceous-Tertiary clay layer?
Kilometer-long fragments of nickel-iron meteorite discovered beneath the Chicxulub crater
The belt is a flattened disk of comets with orbits ranging from near Neptune to out beyond the orbit of Pluto.
Kuiper
About 100 million tons of rock were pulverized during the ______ event, generating about double the energy released by the Mount St. Helens eruption, when a meteorite impacted Arizona about 50,000 years ago.
Meteor Crater
At the time the Alvarez hypothesis was presented to explain the clay layer, no impact crater dating to 65 million years ago was known. Some scientists were unsure if the actual impact crater could be found. Why?
Sixty-five million years had passed since the impact, and the active geology of Earth may have destroyed the crater during that time.
Which of the following statements best describes asteroids?
Small, rocky, metallic, and/or icy masses mostly located between the inner and outer planets
Which of the following occurred as a result of the Chicxulub impact event 65 million years ago? (Select all that apply.)
Soot and dust launched into the air, blocked sunlight, and reduced global temperatures. A massive earthquake occurred. Regional (possibly global) wildfires destroyed vegetation.
Which of the following is not a characteristic of the inner planets?
Spaced far apart
How did Luis and Walter Alvarez know that the iridium clay layer marked the boundary between the Cretaceous and Tertiary periods?
The assemblage of microscopic fossils changes between the older limestone beneath the clay and the younger limestone above it.
Which of the following statements best describes how the Chicxulub impactor hit Earth?
The asteroid hit Earth at a low angle (20 to 30 degrees) coming from the southeast.
Why are comets significant to understanding the origins of life on Earth?
The icy surfaces of comets contain elements that are the building blocks of life.
Which of the following is the only event that did not occur immediately following the Tunguska impact?
The instant deaths of many people
Which of the following observations could you use to distinguish a typical Earth rock from a meteorite?
The outer surface of meteorites have a melted, blackened appearance.
What physical change do meteoroids undergo when they pass through Earth's atmosphere?
The outer surface of the meteoroid melts due to frictional heating
Which pieces of evidence point to the Chicxulub structure as being an impact crater? (Select all that apply.)
The presence of raised inner and outer rings suggestive of a complex crater A thick layer of shattered rock that includes shocked quartz A generally circular shape
When meteorites are recovered at Earth's surface, their interiors often appear well preserved even though their exteriors show evidence of melting. Why is this?
The removal of melted surface materials also removes heat, which protects the interior from melting.
A geologist is investigating an unusual rock formation in the western United States. The geologist discovers multiple specimens of the mineral stishovite. What can the geologist conclude about this rock formation?
The rock formation experienced high-pressure deformation at some point in its history.
NASA identifies a new near-Earth object (NEO) and rates it a 3 on the Torino scale. What does this rating tell you about the NEO?
There is a greater than 1% chance of the NEO causing local destruction.
What happens to the smallest of meteoroids as they pass through Earth's atmosphere?
They pass through.
How far away were tektites spread from the impact event depicted in this image?
To the Gulf of Mexico
True or false: Meteoroids smaller than 0.001 mm pass through the atmosphere relatively easily.
True
The event that occurred in , central Siberia, in 1908 was caused by a meteorite that exploded about 8 km above the Earth's surface.
Tunguska
The Oort cloud is ______.
a diffuse envelope of comets that orbit the Sun beyond the outer plants
In the wake of the meteoroid explosion above Tunguska, Siberia, ______. (Select all that apply.)
a strong light was observed in the nighttime sky in Sweden and Scotland a monstrous blast was heard up to 1,000 km away ground shaking was recorded by seismometers from as far away as Germany
Meteor Crater formed ______.
about 50,000 years ago by the impact of an iron-nickel meteorite
When scientists went to investigate the cause of the Tunguska event, they found an area near the Tunguska River where ______. (Select all that apply.)
about 80 million trees had been knocked down, with many others tilted or disturbed there was no sign of an impact crater
A rubble pile asteroid is formed when ______.
an asteroid is broken during a collision, and the pieces are held together in a collection
Mostly located between the inner and outer planets, are small, rocky, metallic, and/or icy masses.
asteroids
The term , which means "star wound" in Greek, was first used by geologist Robert Diez to describe impact craters.
astrobleme
The Chicxulub asteroid struck Earth at a low angle, as evidenced by the ______ of the crater.
asymmetry
After the Alvarez team brought their findings about the iridium clay layer to light, other scientists began looking for additional clues. They found more evidence to support the Alvarez hypothesis, including a(n) ______. (Select all that apply.)
chaotic, thick sedimentary deposit in Cuba about the same age as the clay layer 65 million-year-old sedimentary layer in Haiti containing shocked quartz and spherules thick bed of sediment in Mexico that appeared to result from a massive tsunami
Halley's is a common visitor to Earth, appearing every 76 years as it travels along its elliptical orbit around the and into the outer solar system.
comet sun
Match the phrases to list ways that an impact scar, e.g., at the K-T boundary, may be destroyed by geologic processes over time.
continental - flow plate - carry sedimentary - cover
Statistics calculated in 1992 suggest that a large asteroid or comet ______.
could do serious damage to human civilization
Impact are formed when meteoroids with weights greater than 350 tons hit Earth's surface.
craters
The word astrobleme ______. (Select all that apply.)
describes impact scars means "star wound"
The ______ impact caused global wildfires, short-time fluctuations in global temperatures, and acid rainfall, which made life very difficult in its aftermath.
end of the Cretaceous
Due to the great velocities at which asteroids and comets are moving, impact events can be catastrophic since they release large amounts of kinetic .
energy
Maria are the dark-colored areas on the Moon that were formed by ______.
flood basalts
Match the phrases to complete a list of evidence scientists used to support the iridium clay layer hypothesis for the Cretaceous-Tertiary boundary.
fluffy - abundant shocked - violent clay - change abundant - composition
A tektite is a ______.
glassy spherule formed by in-air cooling of impact-melted rock
Antarctica is a great place to collect meteorites because ______. (Select all that apply.)
ice flow can concentrate meteorites in one area, making them easier to discover meteorites are stored in the ice, protecting them from weathering and erosion
When a relatively large meteoroid hits Earth's surface, it mostly vaporizes itself and the rock below, creating both a shock wave and a(n) .
impact crater
Put the following sentences in order, top down, to describe the impact crater forming process.
impact most release crater
The Solar System's planets are small, close together, and primarily composed of rocky material. In contrast, the planets are much larger, spaced farther apart, and composed mainly of gases surrounding rocky cores.
inner outer
Luis Alvarez was the first to propose that an asteroid supplied the high amounts of the element found in the Cretaceous-Tertiary boundary clay layer.
iridium
The materials that make up the asteroid belt were unable to clump together to form a planet because of the gravitational influence of .
jupiter
The objects in the Kuiper belt are ______.
left over from the formation of the outer planets
At the end of the Cretaceous, an asteroid struck shallow, tropical seas near the Yucatan Peninsula, Mexico. It vaporized ______ rock, which increased atmospheric CO2 and led to a period of global-warming conditions.
limestone
The dark-colored areas of the Moon, called , are the result of the eruption of flood basalts that covered the surface from 3.8 to 3.2 billion years ago.
maria
If you find a rock that has a glazed, blackened outer crust, indicating that its surface has experienced high temperatures and melting, the rock may be a(n) .
meteorite
The 1908 Tunguska event resulted from a ______.
meteorite exploding about 8 km above the ground
Many of the tektites found in North America were formed when a ______.
meteorite struck Virginia about 35.5 million years ago
A piece of asteroid or comet that orbits the Sun is called a ______. If it enters Earth's atmosphere, it is called a ______. If it hits Earth's surface, it is called a ______.
meteoroid; meteor; meteorite
At the moment of impact, an asteroid or comet is ______.
mostly converted into a superhot vapor
"Stony" meteorites are not commonly found on Earth because they ______. (Select all that apply.)
not easily identified as meteoritic in origin break up readily in the atmosphere weather more rapidly when they reach the ground
The meteoroids that reach Earth atmosphere on a daily basis are ______.
numerous and small
The large envelope of comets that encircle the Sun beyond the outer planets is called the cloud.
oort
Most comets have wildly eccentric orbits, passing very close to the Sun at one point in their orbit (called the ______), but then moving out beyond the outermost planets at the other end of their orbit (called the ______).
perihelion; aphelion
The Moon is "dead" means that the Moon has no ______. (Choose all that apply.)
plate tectonics water life
Rocks that form in the intense heat and associated with meteoroid impacts show rare varieties of quartz minerals, droplets of once-melted metal, and shatter cones.
pressure
The presence of shocked in a layer of shattered rock located in the Chicxulub structure helped convince scientists that it likely originated from an impact event.
quartz
Occasionally, an asteroid may be broken into pieces during a collision, but the energy of the collision is not enough to scatter the pieces. This can result in multiple small bodies bound together by gravity, called a ______.
rubble pile
Since the Moon is geologically dead, many more impact are preserved there than on Earth.
scars
Averaging around 1 mm in diameter, or about the size of a sand grain, ______ usually melt in the atmosphere and create a bright flash of light in the process.
shooting stars
A(n) crater is formed by a smaller meteorite and exhibits a raised outer rim but lacks a central uplift. In contrast, a crater, created by a large meteorite impact, has a collapsed outer rim and a central uplift.
simple complex
Comets are sometimes referred to as "dirty " because they are composed of ice and rocky debris.
snowballs
The mineral ______ often forms at impact sites, where the extremely high pressures of the impact event alter the atomic structure of quartz crystals.
stishovite
In comparison to "iron" meteorites, "" meteorites are rarely collected at Earth's surface because they break up more readily in Earth's atmosphere and weather more rapidly if they do reach the planet's surface.
stony
A comet's tail forms as it nears the Sun because ______.
sunlight causes the outer layers of the comet to sublimate directly to vapor
Short-period comets have orbits that ______. Long-period comets have orbits that ______.
take less than 200 years to complete; take more than 200 years to complete
The Moon is considered a geologically "dead" world because it lacks active plate , which has preserved evidence of its ancient past.
tectonics
As scientists continued to gather evidence in support of the Alvarez hypothesis, all signs pointed to an impact somewhere in ______.
the Caribbean region
The Moon exhibits many more impact craters than Earth because ______.
the Moon is geologically dead, so impact scars are not destroyed
The length of a comet's tail is primarily a function of ______. (Select all that apply.)
the amount of ice cover on the comet's surface distance to the Sun
Foraminifera are microscopic animals commonly preserved as fossils. The change in the assemblage of foraminifera fossils between the limestone rocks above and below a 1 cm thick clay layer indicated to Luis and Walter Alvarez that ______.
the clay layer marked the Cretaceous-Tertiary boundary
The difference between short- and long-period comets is ______.
the duration of their orbits
The objects located within the asteroid belt were unable to form a cohesive planet because ______.
the gravitational acceleration of Jupiter creates asteroid velocities that are too fast to form a planet
Although millions of meteoroids collide with Earth every day, we rarely notice this bombardment because ______.
the planet's atmosphere destroys most of them before they reach the ground
Several lines of evidence suggest that Meteor Crater was formed by an impact event. These include ______. (Select all that apply.)
the presence of stishovite in the crater numerous nickel metallic meteorite fragments discovered nearby steep-sided and closed crater walls
Large stony meteorites, such as the one that possibly caused the Tunguska event, sometimes do not leave craters because ______.
the resistance of Earth's atmosphere causes them to break apart
The most notable observation made in the area where the Tunguska event occurred was that ______.
there was no impact crater or even broken ground
Comets are nicknamed "dirty snowballs" because ______.
they are composed of a mixture of ice and rocky debris
The explosiveness of impact events is not only due to the size of the asteroid or comet, but also the ______.
tremendous amount of energy involved
the presence of stishovite in the crater numerous nickel metallic meteorite fragments discovered nearby steep-sided and closed crater walls
under intense heating under intense pressure
At the end of the Cretaceous, an asteroid struck in shallow tropical water near the Yucatan Peninsula, Mexico. It likely affected short-term climate by ______. (Select all that apply.)
vaporizing limestone rock and increasing atmospheric CO2, leading to global-warming conditions releasing large amounts of dust and soot into the atmosphere, causing short-term cooling
