ĐỀ THI LỚP 9 – ĐỀ SỐ 9 Chào mừng các con Hôm nay chúng ta sẽ cùng thử sức với đề kiểm tra năng lực lớp 9 nhé. Các bạn cần lưu ý thực hiện các yêu cầu sau: Điền đầy đủ Họ tên, Email và các thông tin khác được yêu cầu sau khi bài thi kết thúc Kiểm tra lại các câu trả lời của mình trước khi SUBMIT bài thi Chúc các con làm bài thật tốt Họ và tên Lớp học tại Tâm Nghiêm Số điện thoại Tên cha mẹ Choose the most suitable word or group words by circling the letter A, B or C I’m looking …………………to …………………. from you. at - hear forward - hear forward - hearing Choose the most suitable word or group words by circling the letter A, B, or C This school has an excellent...... reputation repute reputed Choose the most suitable word or group words by circling the letter A, B, or C She said she ………………….. to learn to drive. is going go was going Choose the most suitable word or group words by circling the letter A, B, or C …….. we miss the train, we can get the next one. When If While Choose the most suitable word or group words by circling the letter A, B, or C We met a lot of people ……………….. our holiday. while during for Choose the most suitable word or group words by circling the letter A, B, or C My father speaks English quite ……… well better good Choose the most suitable word or group words by circling the letter A, B, or C He wishes he……………… a good student. was were is Choose the most suitable word or group words by circling the letter A, B, or C He …………… a car carefully since 1999. learnt learns has learnt Choose the most suitable word or group words by circling the letter A, B, or C He asked me what I ………………. doing. were was am Choose the most suitable word or group words by circling the letter A, B, or C If you want to speak English fluently, you ……………………. it more often. must practice can practice to practice Complete the sentence with an appropriate word from the box: level heart dictionary advertisement aspect dormitory You’d better learn by ............all the new words. What ................of learning English do you find difficult? Most foreign students live in .............on campus. You can take the exam at an intermediate or advanced .......... I’ve never seen this word before. Use a.............. to look it up. Question 1: Complete the sentence with an appropriate word from the box: level heart dictionary advertisement aspect dormitory You’d better learn by ............all the new words. What ................of learning English do you find difficult? Most foreign students live in .............on campus. You can take the exam at an intermediate or advanced .......... I’ve never seen this word before. Use a.............. to look it up. Question 2: Complete the sentence with an appropriate word from the box: level heart dictionary advertisement aspect dormitory You’d better learn by ............all the new words. What ................of learning English do you find difficult? Most foreign students live in .............on campus. You can take the exam at an intermediate or advanced .......... I’ve never seen this word before. Use a.............. to look it up. Question 3: Complete the sentence with an appropriate word from the box: level heart dictionary advertisement aspect dormitory You’d better learn by ............all the new words. What ................of learning English do you find difficult? Most foreign students live in .............on campus. You can take the exam at an intermediate or advanced .......... I’ve never seen this word before. Use a.............. to look it up. Question 4: Complete the sentence with an appropriate word from the box: level heart dictionary advertisement aspect dormitory You’d better learn by ............all the new words. What ................of learning English do you find difficult? Most foreign students live in .............on campus. You can take the exam at an intermediate or advanced .......... I’ve never seen this word before. Use a.............. to look it up. Question 5: Read the short passage carefully. Britain is now a highly industrialized country and there are only 238,000 farms in the UK. More and more farmers leave the land because they cannot earn enough money to survive. Only large farms are economic and because of this most British farms are big. The small family farms often have to earn more money by offering bed and breakfast accommodation to tourists. Farming methods in Britain have also changed. Fields used to be quite small, divided by hedges which were sometimes a thousand years old and full of wild flowers and birds. Many hedges were pulled up to allow farmers to use modern machinery. Now most fields in England are large by European standards. Decide whether the following statements are True or False 1. There are more 200,000 farms in England. True False Read the short passage carefully. Britain is now a highly industrialized country and there are only 238,000 farms in the UK. More and more farmers leave the land because they cannot earn enough money to survive. Only large farms are economic and because of this most British farms are big. The small family farms often have to earn more money by offering bed and breakfast accommodation to tourists. Farming methods in Britain have also changed. Fields used to be quite small, divided by hedges which were sometimes a thousand years old and full of wild flowers and birds. Many hedges were pulled up to allow farmers to use modern machinery. Now most fields in England are large by European standards. Decide whether the following statements are True or False 2. All farms are economic. True False Read the short passage carefully. Britain is now a highly industrialized country and there are only 238,000 farms in the UK. More and more farmers leave the land because they cannot earn enough money to survive. Only large farms are economic and because of this most British farms are big. The small family farms often have to earn more money by offering bed and breakfast accommodation to tourists. Farming methods in Britain have also changed. Fields used to be quite small, divided by hedges which were sometimes a thousand years old and full of wild flowers and birds. Many hedges were pulled up to allow farmers to use modern machinery. Now most fields in England are large by European standards. Decide whether the following statements are True or False 3. Fields are quite small. True False Read the short passage carefully. Britain is now a highly industrialized country and there are only 238,000 farms in the UK. More and more farmers leave the land because they cannot earn enough money to survive. Only large farms are economic and because of this most British farms are big. The small family farms often have to earn more money by offering bed and breakfast accommodation to tourists. Farming methods in Britain have also changed. Fields used to be quite small, divided by hedges which were sometimes a thousand years old and full of wild flowers and birds. Many hedges were pulled up to allow farmers to use modern machinery. Now most fields in England are large by European standards. Decide whether the following statements are True or False 4. Farming methods in Britain have also changed. True False Rewrite these sentences , beginning with the suggested words or phrases: “This picture is very nice,” my uncle said. My uncle said ........... Rewrite these sentences , beginning with the suggested words or phrases: “When does your school vacation start?” She asked me …….......... Rewrite these sentences , beginning with the suggested words or phrases: We can’t live together forever. I wish .................. Rewrite these sentences , beginning with the suggested words or phrases: The students should wear uniforms when they are at school. Uniforms ............… Supply the appropriate tenses/ forms of the verbs in brackets It is high time that nurses (GIVE) better pay and conditions. Supply the appropriate tenses/ forms of the verbs in brackets We whispered lest other people (HEAR) what we were talking about. Supply the appropriate tenses/ forms of the verbs in brackets It (NOT BE) Phong that you saw yesterday; he was upon arrival to his homeland. Supply the appropriate tenses/ forms of the verbs in brackets He treats me as if he (BE) my boyfriend. Supply the appropriate tenses/ forms of the verbs in brackets Florida, (KNOW) as the sunshine state, attracts many tourists every year. Read the passage, and then circle the correct answer for each question. The atmosphere that originally surrounded Earth was probably much different from the air we breathe today. Earth’s first atmosphere (some 4.6 billion years ago) was most likely hydrogen and helium. The two most abundant gasses found in the universe -as well as hydrogen compounds, such as methane and ammonia, Most scientists feel that this early atmosphere escaped into space from the Earth’s hot surface.A second, more dense atmosphere, however, gradually envelopedEarth as gasses from molten rocks within its hot interior escaped through volcanoes and steam vents. We assume that volcanoes spewed out the same gasses then as they do today: mostly water vapor (about 80 percent), carbon dioxide (about ten percent), and up to a few percent nitrogen. These same gasses probably created Earth's second atmosphere.As millions of years passed, the constant outpouring of gasses from the hot interior -known as outgassing -provided a rich supply of water vapor, which formed into clouds. Rain fell upon Earth for many thousands or years, forming the rivers, lakes, and oceans of the world. During this Lime, large amounts of carbon dioxide were dissolved in the oceans. Through chemical and biological processes, much of the carbon dioxide became locked up in carbon sedimentary rocks, such as limestone. With much of the water vapor already condensed into water and the concentration of carbon dioxide dwindling, the atmosphere graduallybecame rich nitrogen.It appears that oxygen, the second most abundant gas in today’s atmosphere, probably began an extremely slow increase in concentration as energetic rays from the sun split water vapor into hydrogen and oxygen during a process called photodissociation. The hydrogen, being lighter, probably rose and escaped into space, while the oxygen remained in the atmosphere.This slow increase in oxygen may have provided enough of this gas for primitive plants to evolve, perhaps two to three billion years ago. Orthe plants may have evolved in an almost oxygen-free (anaerobic) environment. At any rate, plant growth greatly enriched our atmosphere with oxygen. The reason for this enrichment is that plants, in the presence of sunlight, process carbon dioxide and water to produce oxygen.The word “they” in line 8 refers to ........... gasses volcanoes steam vents rocks Read the passage, and then circle the correct answer for each question. The atmosphere that originally surrounded Earth was probably much different from the air we breathe today. Earth’s first atmosphere (some 4.6 billion years ago) was most likely hydrogen and helium. The two most abundant gasses found in the universe -as well as hydrogen compounds, such as methane and ammonia, Most scientists feel that this early atmosphere escaped into space from the Earth’s hot surface.A second, more dense atmosphere, however, gradually envelopedEarth as gasses from molten rocks within its hot interior escaped through volcanoes and steam vents. We assume that volcanoes spewed out the same gasses then as they do today: mostly water vapor (about 80 percent), carbon dioxide (about ten percent), and up to a few percent nitrogen. These same gasses probably created Earth's second atmosphere.As millions of years passed, the constant outpouring of gasses from the hot interior -known as outgassing -provided a rich supply of water vapor, which formed into clouds. Rain fell upon Earth for many thousands or years, forming the rivers, lakes, and oceans of the world. During this Lime, large amounts of carbon dioxide were dissolved in the oceans. Through chemical and biological processes, much of the carbon dioxide became locked up in carbon sedimentary rocks, such as limestone. With much of the water vapor already condensed into water and the concentration of carbon dioxide dwindling, the atmosphere graduallybecame rich nitrogen.It appears that oxygen, the second most abundant gas in today’s atmosphere, probably began an extremely slow increase in concentration as energetic rays from the sun split water vapor into hydrogen and oxygen during a process called photodissociation. The hydrogen, being lighter, probably rose and escaped into space, while the oxygen remained in the atmosphere.This slow increase in oxygen may have provided enough of this gas for primitive plants to evolve, perhaps two to three billion years ago. Orthe plants may have evolved in an almost oxygen-free (anaerobic) environment. At any rate, plant growth greatly enriched our atmosphere with oxygen. The reason for this enrichment is that plants, in the presence of sunlight, process carbon dioxide and water to produce oxygen.The word “enveloped”in line 6 is closest in meaning to ............... surrounded changed escaped characterized Read the passage, and then circle the correct answer for each question. The atmosphere that originally surrounded Earth was probably much different from the air we breathe today. Earth’s first atmosphere (some 4.6 billion years ago) was most likely hydrogen and helium. The two most abundant gasses found in the universe -as well as hydrogen compounds, such as methane and ammonia. Most scientists feel that this early atmosphere escaped into space from the Earth’s hot surface.A second, more dense atmosphere, however, gradually enveloped Earth as gasses from molten rocks within its hot interior escaped through volcanoes and steam vents. We assume that volcanoes spewed out the same gasses then as they do today: mostly water vapor (about 80 percent), carbon dioxide (about ten percent), and up to a few percent nitrogen. These same gasses probably created Earth's second atmosphere.As millions of years passed, the constant outpouring of gasses from the hot interior -known as outgassing -provided a rich supply of water vapor, which formed into clouds. Rain fell upon Earth for many thousands or years, forming the rivers, lakes, and oceans of the world. During this Lime, large amounts of carbon dioxide were dissolved in the oceans. Through chemical and biological processes, much of the carbon dioxide became locked up in carbon sedimentary rocks, such as limestone. With much of the water vapor already condensed into water and the concentration of carbon dioxide dwindling, the atmosphere gradually became rich nitrogen.It appears that oxygen, the second most abundant gas in today’s atmosphere, probably began an extremely slow increase in concentration as energetic rays from the sun split water vapor into hydrogen and oxygen during a process called photodissociation. The hydrogen, being lighter, probably rose and escaped into space, while the oxygen remained in the atmosphere.This slow increase in oxygen may have provided enough of this gas for primitive plants to evolve, perhaps two to three billion years ago. Or the plants may have evolved in an almost oxygen-free (anaerobic) environment. At any rate, plant growth greatly enriched our atmosphere with oxygen. The reason for this enrichment is that plants, in the presence of sunlight, process carbon dioxide and water to produce oxygen.The word “gradually”in line 18is closest in meaning to ........... accidentally quickly in the end by degrees Read the passage, and then circle the correct answer for each question. The atmosphere that originally surrounded Earth was probably much different from the air we breathe today. Earth’s first atmosphere (some 4.6 billion years ago) was most likely hydrogen and helium. The two most abundant gasses found in the universe -as well as hydrogen compounds, such as methane and ammonia. Most scientists feel that this early atmosphere escaped into space from the Earth’s hot surface.A second, more dense atmosphere, however, gradually enveloped Earth as gasses from molten rocks within its hot interior escaped through volcanoes and steam vents. We assume that volcanoes spewed out the same gasses then as they do today: mostly water vapor (about 80 percent), carbon dioxide (about ten percent), and up to a few percent nitrogen. These same gasses probably created Earth's second atmosphere.As millions of years passed, the constant outpouring of gasses from the hot interior -known as outgassing -provided a rich supply of water vapor, which formed into clouds. Rain fell upon Earth for many thousands or years, forming the rivers, lakes, and oceans of the world. During this Lime, large amounts of carbon dioxide were dissolved in the oceans. Through chemical and biological processes, much of the carbon dioxide became locked up in carbon sedimentary rocks, such as limestone. With much of the water vapor already condensed into water and the concentration of carbon dioxide dwindling, the atmosphere gradually became rich nitrogen.It appears that oxygen, the second most abundant gas in today’s atmosphere, probably began an extremely slow increase in concentration as energetic rays from the sun split water vapor into hydrogen and oxygen during a process called photodissociation. The hydrogen, being lighter, probably rose and escaped into space, while the oxygen remained in the atmosphere.This slow increase in oxygen may have provided enough of this gas for primitive plants to evolve, perhaps two to three billion years ago. Or the plants may have evolved in an almost oxygen-free (anaerobic) environment. At any rate, plant growth greatly enriched our atmosphere with oxygen. The reason for this enrichment is that plants, in the presence of sunlight, process carbon dioxide and water to produce oxygen.The author uses the word “Or”in line 25 to ................ criticize the previous suggestion provide unrelated information propose a similar idea suggest an alternative Read the passage, and then circle the correct answer for each question. The atmosphere that originally surrounded Earth was probably much different from the air we breathe today. Earth’s first atmosphere (some 4.6 billion years ago) was most likely hydrogen and helium. The two most abundant gasses found in the universe -as well as hydrogen compounds, such as methane and ammonia. Most scientists feel that this early atmosphere escaped into space from the Earth’s hot surface.A second, more dense atmosphere, however, gradually enveloped Earth as gasses from molten rocks within its hot interior escaped through volcanoes and steam vents. We assume that volcanoes spewed out the same gasses then as they do today: mostly water vapor (about 80 percent), carbon dioxide (about ten percent), and up to a few percent nitrogen. These same gasses probably created Earth's second atmosphere.As millions of years passed, the constant outpouring of gasses from the hot interior -known as outgassing -provided a rich supply of water vapor, which formed into clouds. Rain fell upon Earth for many thousands or years, forming the rivers, lakes, and oceans of the world. During this Lime, large amounts of carbon dioxide were dissolved in the oceans. Through chemical and biological processes, much of the carbon dioxide became locked up in carbon sedimentary rocks, such as limestone. With much of the water vapor already condensed into water and the concentration of carbon dioxide dwindling, the atmosphere gradually became rich nitrogen.It appears that oxygen, the second most abundant gas in today’s atmosphere, probably began an extremely slow increase in concentration as energetic rays from the sun split water vapor into hydrogen and oxygen during a process called photodissociation. The hydrogen, being lighter, probably rose and escaped into space, while the oxygen remained in the atmosphere.This slow increase in oxygen may have provided enough of this gas for primitive plants to evolve, perhaps two to three billion years ago. Or the plants may have evolved in an almost oxygen-free (anaerobic) environment. At any rate, plant growth greatly enriched our atmosphere with oxygen. The reason for this enrichment is that plants, in the presence of sunlight, process carbon dioxide and water to produce oxygen.The author organizes the discussion of the Earth’s atmosphere in terms of the ............ role of volcanoes in its formation occur in which changes time it took for the Earth’s surface: to cool and nitrogen to appear chemical and physical features of gasses Read the passage, and then circle the correct answer for each question. The atmosphere that originally surrounded Earth was probably much different from the air we breathe today. Earth’s first atmosphere (some 4.6 billion years ago) was most likely hydrogen and helium. The two most abundant gasses found in the universe -as well as hydrogen compounds, such as methane and ammonia, Most scientists feel that this early atmosphere escaped into space from the Earth’s hot surface.A second, more dense atmosphere, however, gradually envelopedEarth as gasses from molten rocks within its hot interior escaped through volcanoes and steam vents. We assume that volcanoes spewed out the same gasses then as they do today: mostly water vapor (about 80 percent), carbon dioxide (about ten percent), and up to a few percent nitrogen. These same gasses probably created Earth's second atmosphere.As millions of years passed, the constant outpouring of gasses from the hot interior -known as outgassing -provided a rich supply of water vapor, which formed into clouds. Rain fell upon Earth for many thousands or years, forming the rivers, lakes, and oceans of the world. During this Lime, large amounts of carbon dioxide were dissolved in the oceans. Through chemical and biological processes, much of the carbon dioxide became locked up in carbon sedimentary rocks, such as limestone. With much of the water vapor already condensed into water and the concentration of carbon dioxide dwindling, the atmosphere graduallybecame rich nitrogen.It appears that oxygen, the second most abundant gas in today’s atmosphere, probably began an extremely slow increase in concentration as energetic rays from the sun split water vapor into hydrogen and oxygen during a process called photodissociation. The hydrogen, being lighter, probably rose and escaped into space, while the oxygen remained in the atmosphere.This slow increase in oxygen may have provided enough of this gas for primitive plants to evolve, perhaps two to three billion years ago. Orthe plants may have evolved in an almost oxygen-free (anaerobic) environment. At any rate, plant growth greatly enriched our atmosphere with oxygen. The reason for this enrichment is that plants, in the presence of sunlight, process carbon dioxide and water to produce oxygen.What is the main idea of the passage? The original atmosphere on Earth was unstable. The atmosphere on Earth has changed over time. The atmosphere on Earth has changed over time. Plant growth depended on oxygen in the Earth’s atmosphere. Read the passage, and then circle the correct answer for each question. The atmosphere that originally surrounded Earth was probably much different from the air we breathe today. Earth’s first atmosphere (some 4.6 billion years ago) was most likely hydrogen and helium. The two most abundant gasses found in the universe -as well as hydrogen compounds, such as methane and ammonia, Most scientists feel that this early atmosphere escaped into space from the Earth’s hot surface.A second, more dense atmosphere, however, gradually envelopedEarth as gasses from molten rocks within its hot interior escaped through volcanoes and steam vents. We assume that volcanoes spewed out the same gasses then as they do today: mostly water vapor (about 80 percent), carbon dioxide (about ten percent), and up to a few percent nitrogen. These same gasses probably created Earth's second atmosphere.As millions of years passed, the constant outpouring of gasses from the hot interior -known as outgassing -provided a rich supply of water vapor, which formed into clouds. Rain fell upon Earth for many thousands or years, forming the rivers, lakes, and oceans of the world. During this Lime, large amounts of carbon dioxide were dissolved in the oceans. Through chemical and biological processes, much of the carbon dioxide became locked up in carbon sedimentary rocks, such as limestone. With much of the water vapor already condensed into water and the concentration of carbon dioxide dwindling, the atmosphere graduallybecame rich nitrogen.It appears that oxygen, the second most abundant gas in today’s atmosphere, probably began an extremely slow increase in concentration as energetic rays from the sun split water vapor into hydrogen and oxygen during a process called photodissociation. The hydrogen, being lighter, probably rose and escaped into space, while the oxygen remained in the atmosphere.This slow increase in oxygen may have provided enough of this gas for primitive plants to evolve, perhaps two to three billion years ago. Orthe plants may have evolved in an almost oxygen-free (anaerobic) environment. At any rate, plant growth greatly enriched our atmosphere with oxygen. The reason for this enrichment is that plants, in the presence of sunlight, process carbon dioxide and water to produce oxygen.According to the passage, outgassing eventually led to all of the following EXCEPT ........... increases in the carbon dioxide content of sedimentary rocks the formation of bodies of water decreases in the level of nitrogen the formation of clouds Read the passage, and then circle the correct answer for each question. The atmosphere that originally surrounded Earth was probably much different from the air we breathe today. Earth’s first atmosphere (some 4.6 billion years ago) was most likely hydrogen and helium. The two most abundant gasses found in the universe -as well as hydrogen compounds, such as methane and ammonia. Most scientists feel that this early atmosphere escaped into space from the Earth’s hot surface.A second, more dense atmosphere, however, gradually enveloped Earth as gasses from molten rocks within its hot interior escaped through volcanoes and steam vents. We assume that volcanoes spewed out the same gasses then as they do today: mostly water vapor (about 80 percent), carbon dioxide (about ten percent), and up to a few percent nitrogen. These same gasses probably created Earth's second atmosphere.As millions of years passed, the constant outpouring of gasses from the hot interior -known as outgassing -provided a rich supply of water vapor, which formed into clouds. Rain fell upon Earth for many thousands or years, forming the rivers, lakes, and oceans of the world. During this Lime, large amounts of carbon dioxide were dissolved in the oceans. Through chemical and biological processes, much of the carbon dioxide became locked up in carbon sedimentary rocks, such as limestone. With much of the water vapor already condensed into water and the concentration of carbon dioxide dwindling, the atmosphere gradually became rich nitrogen.It appears that oxygen, the second most abundant gas in today’s atmosphere, probably began an extremely slow increase in concentration as energetic rays from the sun split water vapor into hydrogen and oxygen during a process called photodissociation. The hydrogen, being lighter, probably rose and escaped into space, while the oxygen remained in the atmosphere.This slow increase in oxygen may have provided enough of this gas for primitive plants to evolve, perhaps two to three billion years ago. Or the plants may have evolved in an almost oxygen-free (anaerobic) environment. At any rate, plant growth greatly enriched our atmosphere with oxygen. The reason for this enrichment is that plants, in the presence of sunlight, process carbon dioxide and water to produce oxygen.The phase “At any rate” in line 26 is closest in meaning to ............ regardless in addition although unlikely fortunately Read the passage, and then circle the correct answer for each question. The atmosphere that originally surrounded Earth was probably much different from the air we breathe today. Earth’s first atmosphere (some 4.6 billion years ago) was most likely hydrogen and helium. The two most abundant gasses found in the universe -as well as hydrogen compounds, such as methane and ammonia. Most scientists feel that this early atmosphere escaped into space from the Earth’s hot surface.A second, more dense atmosphere, however, gradually enveloped Earth as gasses from molten rocks within its hot interior escaped through volcanoes and steam vents. We assume that volcanoes spewed out the same gasses then as they do today: mostly water vapor (about 80 percent), carbon dioxide (about ten percent), and up to a few percent nitrogen. These same gasses probably created Earth's second atmosphere.As millions of years passed, the constant outpouring of gasses from the hot interior -known as outgassing -provided a rich supply of water vapor, which formed into clouds. Rain fell upon Earth for many thousands or years, forming the rivers, lakes, and oceans of the world. During this Lime, large amounts of carbon dioxide were dissolved in the oceans. Through chemical and biological processes, much of the carbon dioxide became locked up in carbon sedimentary rocks, such as limestone. With much of the water vapor already condensed into water and the concentration of carbon dioxide dwindling, the atmosphere gradually became rich nitrogen.It appears that oxygen, the second most abundant gas in today’s atmosphere, probably began an extremely slow increase in concentration as energetic rays from the sun split water vapor into hydrogen and oxygen during a process called photodissociation. The hydrogen, being lighter, probably rose and escaped into space, while the oxygen remained in the atmosphere.This slow increase in oxygen may have provided enough of this gas for primitive plants to evolve, perhaps two to three billion years ago. Or the plants may have evolved in an almost oxygen-free (anaerobic) environment. At any rate, plant growth greatly enriched our atmosphere with oxygen. The reason for this enrichment is that plants, in the presence of sunlight, process carbon dioxide and water to produce oxygen.Which of the following does the passage mention as necessary for both the production of oxygen by photodissociation and the production of oxygen by plants? Water Hydrogen Carbon dioxide Nitrogen Read the passage, and then circle the correct answer for each question. The atmosphere that originally surrounded Earth was probably much different from the air we breathe today. Earth’s first atmosphere (some 4.6 billion years ago) was most likely hydrogen and helium. The two most abundant gasses found in the universe -as well as hydrogen compounds, such as methane and ammonia. Most scientists feel that this early atmosphere escaped into space from the Earth’s hot surface.A second, more dense atmosphere, however, gradually enveloped Earth as gasses from molten rocks within its hot interior escaped through volcanoes and steam vents. We assume that volcanoes spewed out the same gasses then as they do today: mostly water vapor (about 80 percent), carbon dioxide (about ten percent), and up to a few percent nitrogen. These same gasses probably created Earth's second atmosphere.As millions of years passed, the constant outpouring of gasses from the hot interior -known as outgassing -provided a rich supply of water vapor, which formed into clouds. Rain fell upon Earth for many thousands or years, forming the rivers, lakes, and oceans of the world. During this Lime, large amounts of carbon dioxide were dissolved in the oceans. Through chemical and biological processes, much of the carbon dioxide became locked up in carbon sedimentary rocks, such as limestone. With much of the water vapor already condensed into water and the concentration of carbon dioxide dwindling, the atmosphere gradually became rich nitrogen.It appears that oxygen, the second most abundant gas in today’s atmosphere, probably began an extremely slow increase in concentration as energetic rays from the sun split water vapor into hydrogen and oxygen during a process called photodissociation. The hydrogen, being lighter, probably rose and escaped into space, while the oxygen remained in the atmosphere.This slow increase in oxygen may have provided enough of this gas for primitive plants to evolve, perhaps two to three billion years ago. Or the plants may have evolved in an almost oxygen-free (anaerobic) environment. At any rate, plant growth greatly enriched our atmosphere with oxygen. The reason for this enrichment is that plants, in the presence of sunlight, process carbon dioxide and water to produce oxygen.The passage suggests that oxygen remained in the atmosphere because ............ it was caused by outgassing it was heavier than hydrogen hydrogen became trapped in limestone rays from the sun created equal amounts of hydrogen and oxygen 1 out of 38