Gravity IELTS Reading: Decoding the Passage

Have you ever heard of a place on Earth where you actually weigh a little less than usual? It’s not magic—it’s a real physical phenomenon occurring in Hudson Bay, Canada! The “Gravity” reading passage in the IELTS exam takes us on a journey from the ancient hypotheses of Aristotle and Galileo to modern satellite discoveries that decode this strange gravitational dip.

The ECE Language Center is here to help you break down the vocabulary, provide a detailed translation, and find the correct answers for the questions in this passage!

Reading Passage & Questions

Reading Passage: GRAVITY

A. Without gravitational forces, Earth and other planets would be unable to stay in their orbits around the Sun. The Moon would be unable to orbit the Earth, tidal waves would not occur, and the rising of hot air or water convection would be impossible. Gravitation is a phenomenon that allows objects to attract other matter; the physics behind it has been explained in the Theory of Relativity and Newton’s Law of Universal Gravitation, though attempts to explain gravity date back to ancient times. In the 4th Century B.C., the Greek philosopher Aristotle developed the hypothesis that all objects were drawn into their correct position by crystalline spheres and that a physical mass would fall towards the earth in direct proportion to its weight.

B. In the late 16th century, Galileo deduced that while gravitation propels all objects to the ground at the same rate, air resistance resulted in heavier objects appearing to fall more quickly; his theories contradicted earlier belief systems established by Aristotle and others, paving the way for the formulation of modern theories. Though the two terms are now used interchangeably in layman’s terms, strictly by scientific definition, there are distinct differences between ‘gravitation’ and ‘gravity’. The first relates to the influence exerted by different objects which allow them to attract other objects, whereas ‘gravity’ refers specifically to the force possessed by such objects which facilitates gravitation. Certain scientific theories hold that gravitation may be initiated by a combination of factors and not simply the existence of gravity alone, though doubts have been raised regarding some of these theories.

C. Gravity is directly proportional to mass; a smaller object possesses less gravity. To illustrate, the Moon is a quarter of the Earth’s size and possesses only 1/6 of its gravity. The mass of the Earth itself is not spread out proportionally, being flatter at the poles than at the equator as a result of its rotation; gravity and gravitational pull in different locations throughout the world also vary. In the 1960s, as a result of research into worldwide gravity fields, it was discovered that, inexplicably, areas around and including the Hudson Bay area of Canada appeared to possess significantly lower levels of gravity than other parts of the globe; the reasons for this dissimilarity have since been extensively investigated, resulting in two explanations.

D. The original theory presented attributed this anomaly to activity occurring 100-200 kilometres below the Earth’s surface within the layer known as the ‘mantle’. The mantle is comprised of hot molten rock known as magma, which flows under the earth’s surface causing convection currents. These convection currents can result in the lowering of the continental plates that make up the Earth’s surface; as a result, when this occurs, the mass in that area and its gravity are also reduced. Research findings indicated that such activity had occurred in the Hudson Bay region.

E. More recently, a second conjecture suggested that, in fact, lower levels of gravity in the area are a result of occurrences during the Ice Age. The Laurentide ice sheet, which covered most of Canada and the northern tip of the USA until it melted 10,000 years ago, is thought to have been 3.2 kms thick in most parts and 3.7 kms thick over two areas of Hudson Bay. The sheer weight of the ice layer weighed down the surface of the earth below, leaving a deep indentation once it had melted, having caused the area around Hudson Bay to become thinner as the earth’s surface was pushed to the edges of the ice sheet.

F. Extensive investigation has since been carried out by the Harvard-Smithsonian Center for Astrophysics using data collected by satellites during the Gravity Recovery and Climate Experiment (GRACE) between 2002 and 2006. The satellites are placed 220kms apart and orbit 500kms above Earth. Being extremely sensitive to even minor differences in the gravitational pull of the areas of earth they pass over, as the first satellite enters an area with decreased gravity, it moves slightly away from the earth as the gravitational pull is reduced and also moves slightly further away from the sister satellite that follows, such activity allowing scientists to create maps of gravitational fields. The GRACE findings also allowed scientists to estimate the appearance of Hudson Bay over 10,000 years ago, prior to the great thaw. The areas possessing the lowest gravity today correlate with the areas covered in the thickest layers of ice at that time.

G. Researchers now believe that both theories regarding reduced gravity levels in the Hudson Bay region are accurate and that the area’s characteristics are a result of both magma activity and the impact of the Laurentide ice sheet. It has been estimated that the former has resulted in 55-75% of gravity reduction and that pressure resulting from the latter accounts for 25-45%.

H. The effects of the Laurentide ice sheet are reversible due to the earth layer’s capability to ‘rebound’ in response to the removal of the weight which once restricted it. Returning to the original position, however, is an extremely slow process; it is estimated that the area around Hudson Bay will take a further 5,000 years to recover the altitude it once possessed prior to the Laurentide ice sheet. The rebound activity in the area is also measurable through observation of sea levels; unlike the rest of the world, sea levels are not rising in the area as a result of melting icecaps, but are dropping as the land recovers its previous form.

I. Research conducted into the Laurentide ice sheet has significant implications on a global scale. The increased knowledge of how that particular area has changed over time and the long-term implications activity in the Ice Age had, paves the way to a better understanding of how current changes elsewhere will manifest themselves over the long term.

Questions

Questions 1-6 The Reading Passage has nine paragraphs A-I. Choose the correct heading for paragraphs B, C and E-H from the list of headings below. Write the correct number i-x in boxes 1-6.

List of Headings

i. Return to previous form

ii. Substantiating a hypothesis

iii. Historic theories

iv. The general rule of gravity and an exception

v. The initial explanation

vi. How proximity to the poles affected Hudson Bay

vii. Scientific definition and contemporary views viii. Relevance to our future ix. An alternative view point x. Consolidating theories

1. Paragraph B

2. Paragraph C

3. Paragraph E

4. Paragraph F

5. Paragraph G

6. Paragraph H

Questions 7-11 Do the following statements agree with the information given in the Reading Passage?

TRUE if the statement agrees with the information

FALSE if the statement contradicts the information

NOT GIVEN if there is no information on this

7. Differentiation between gravity and gravitational pull is generally only made by academics in the field.

8. Gravity levels in areas around the equator are significantly higher than around the poles.

9. It was first believed that lower gravity levels in Hudson Bay could be attributed to its location between the poles and the equator.

10. Molten rock activity within the magma layer has had less of an impact on gravity levels in the Hudson Bay area than the Laurentide ice sheet.

11. The GRACE project’s main focus was areas of Canada and North America once thought to be covered by the Laurentide ice sheet.

Questions 12-15 Complete the sentences below with words from the box below. Write the correct letter A-J.

12. The impact of ________ on objects falling to the ground was not considered by Aristotle.

13. Investigations of ________ first led to the discovery of the unusual levels in Hudson Bay.

14. The earth’s surface has been observed to sink as a direct result of ________.

15. The largest proportion of the Laurentide ice sheet was ________ in depth.

Box of words:

A. crystalline spheres

B. mass

C. 3.2kms

D. continental plates

E. gravity fields

F. warming

G. 3.5kms

H. mantle layers

I. convection currents

J. air resistance

Complete Translation of the Reading Passage

GRAVITY

A. Without gravitational forces, Earth and other planets would be unable to stay in their orbits around the Sun, the Moon would be unable to orbit the Earth, tidal waves would not occur, and the rising of hot air or water convection would be impossible. Gravitation is a phenomenon that allows objects to attract other matter; the physics behind it has been explained in the Theory of Relativity and Newton’s Law of Universal Gravitation, though attempts to explain gravity date back to ancient times. In the 4th Century B.C., the Greek philosopher Aristotle developed the hypothesis that all objects were drawn into their correct position by crystalline spheres and that a physical mass would fall towards the earth in direct proportion to its weight.

B. In the late 16th century, Galileo deduced that while gravitation propels all objects to the ground at the same rate, air resistance results in heavier objects appearing to fall more quickly; his theories contradicted earlier belief systems established by Aristotle and others, paving the way for the formulation of modern theories. Though the two terms are now used interchangeably in layman’s terms, strictly by scientific definition, there are distinct differences between ‘gravitation’ and ‘gravity’. Gravitation relates to the influence exerted by different objects that allows them to attract other objects, whereas ‘gravity’ refers specifically to the force possessed by such objects that facilitates gravitation. Certain scientific theories hold that gravitation may be initiated by a combination of factors and not simply the existence of gravity alone, though doubts have been raised regarding some of these theories.

C. Gravity is directly proportional to mass; a smaller object possesses less gravity. To illustrate, the Moon is a quarter of the Earth’s size and possesses only 1/6 of its gravity. The mass of the Earth itself is not spread out proportionally, being flatter at the poles than at the equator as a result of its rotation; gravity and gravitational pull in different locations throughout the world also vary. In the 1960s, as a result of research into worldwide gravity fields, it was discovered that, inexplicably, areas around and including the Hudson Bay area of Canada appeared to possess significantly lower levels of gravity than other parts of the globe; the reasons for this dissimilarity have since been extensively investigated, resulting in two explanations.

D. The original theory presented attributed this anomaly to activity occurring 100-200 km below the Earth’s surface, within the layer known as the ‘mantle’. The mantle is comprised of hot molten rock known as magma, which flows under the earth’s surface causing convection currents. These convection currents can result in the lowering of the continental plates that make up the Earth’s surface; as a result, when this occurs, the mass in that area and its gravity are also reduced. Research findings indicated that such activity had occurred in the Hudson Bay region.

E. More recently, a second conjecture suggested that, in fact, lower levels of gravity in the area are a result of occurrences during the Ice Age. The Laurentide ice sheet, which covered most of Canada and the northern tip of the USA until it melted 10,000 years ago, is thought to have been 3.2 km thick in most parts and 3.7 km thick over two areas of Hudson Bay. The sheer weight of the ice layer weighed down the surface of the earth below, leaving a deep indentation once it had melted, having caused the area around Hudson Bay to become thinner as the earth’s surface was pushed to the edges of the ice sheet.

F. Extensive investigation has since been carried out by the Harvard-Smithsonian Center for Astrophysics using data collected by satellites during the Gravity Recovery and Climate Experiment (GRACE) between 2002 and 2006. The satellites are placed 220 km apart and orbit 500 km above Earth. Being extremely sensitive to even minor differences in the gravitational pull of the areas of earth they pass over, as the first satellite enters an area with decreased gravity, it moves slightly away from the earth as the gravitational pull is reduced and also moves slightly further away from the sister satellite that follows; such activity allows scientists to create maps of gravitational fields. The GRACE findings also allowed scientists to estimate the appearance of Hudson Bay over 10,000 years ago, prior to the great thaw. The areas possessing the lowest gravity today correlate with the areas covered in the thickest layers of ice at that time.

G. Researchers now believe that both theories regarding reduced gravity levels in the Hudson Bay region are accurate and that the area’s characteristics are a result of both magma activity and the impact of the Laurentide ice sheet. It has been estimated that the former has resulted in 55-75% of gravity reduction and that pressure resulting from the latter accounts for 25-45%.

H. The effects of the Laurentide ice sheet are reversible due to the earth layer’s capability to ‘rebound’ in response to the removal of the weight which once restricted it. Returning to the original position, however, is an extremely slow process; it is estimated that the area around Hudson Bay will take a further 5,000 years to recover the altitude it once possessed prior to the Laurentide ice sheet. The rebound activity in the area is also measurable through observation of sea levels; unlike the rest of the world, sea levels are not rising in the area as a result of melting icecaps, but are dropping as the land recovers its previous form.

I. Research conducted into the Laurentide ice sheet has significant implications on a global scale. The increased knowledge of how that particular area has changed over time and the long-term implications activity in the Ice Age had, paves the way to a better understanding of how current changes elsewhere will manifest themselves over the long term.

Summary of Key Vocabulary

• Propel (v): To push or drive forward.

• Interchangeably (adv): In a way that can be exchanged or substituted.

• Convection currents (n): Currents in a fluid that result from convection.

• Mantle (n): The layer of the earth between the crust and the core.

• Indentation (n): A deep recess or notch in a surface.

• Thaw (n/v): The melting of ice or snow.

• Rebound (v): To bounce back or recover.

• Manifest (v): To display or show clearly.

Answers and Detailed Explanations

1. vii (Scientific definition and contemporary views)

Explanation for Paragraph B: The second half of paragraph B focuses on explaining the strict scientific definition to distinguish between ‘gravitation’ and ‘gravity’. It also mentions contemporary scientific views regarding the factors that initiate gravitational force.

2. iv (The general rule of gravity and an exception)

Explanation for Paragraph C: Paragraph C presents the general rule: “Gravity is directly proportional to mass.” It then provides an exception: the Hudson Bay area has an unusually low level of gravity compared to that rule.

3. ix (An alternative view point)

Explanation for Paragraph E: After paragraph D presents the first theory (about magma convection currents), paragraph E begins with: “More recently a second conjecture suggested that…” This is an alternative viewpoint regarding the Ice Age.

4. ii (Substantiating a hypothesis)

Explanation for Paragraph F: This paragraph describes how scientists used GRACE satellites to investigate and collect empirical data. The results “correlate with” the thickness of the ice. The process of using measured data to prove a hypothesis is called “substantiating a hypothesis.”

5. x (Consolidating theories)

Explanation for Paragraph G: This paragraph concludes that “both theories… are accurate” and provides specific percentages combining both causes (55-75% due to magma, 25-45% due to ice). This act of combining is “consolidating.”

6. i (Return to previous form)

Explanation for Paragraph H: Paragraph H discusses the ‘rebound’ capability of the Earth’s surface and the process of “returning to the original position.” This matches perfectly with the heading “Return to previous form.”

7. TRUE

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