A huge marine mammal known as Steller’s sea cow once lived in the waters around Bering Island off the coast of Siberia. It was described in 1741 by Georg W. Steller, a naturalist who was among the first Europeans to see one. In 1768 the animal became extinct. The reasons for the extinction are not clear. Here are three theories about the main cause of the extinction. First, the sea cows may have been overhunted by groups of native Siberian people. If this theory is correct, then the sea cow population would have originally been quite large, but hundreds of years off too much hunting by the native people diminished the number of sea cows. Sea cows were a good source of food in a harsh environment, so overhunting by native people could have been the main cause of extinction. Second, the sea cow population may have become extinct because of ecosystems disturbances that caused a decline in their main source of food, kelp (a type of sea plant). Kelp populations respond negatively to a number of ecological changes. It is possible that ecological changes near Bering Island some time before 1768 caused a decrease of the kelp that the sea cows depend on. Third, the main cause of extinction of the sea cows could have been European fur traders who came to the island after 1741. It is recorded that the fur traders caught the last sea cow in 1768. It thus seems reasonable to believe that hunting by European fur traders, who possessed weapons that allowed them to quickly kill a large number of the animals, was the main cause of the sea cow’s extinction.
The lecturer challenges the topic proposed in the reading that here are three theories about the main cause of the extinction. And he thinks that we still do not know the exact main cause because each theory has problems.
First, the passage indicates that the sea cows may have been overhunted by groups of native Siberian people. However, the professor points out that a sea cow is 9 meters long and 10 tons weight which is enormous. Nonetheless the population of native Siberian people is not very large, so they cannot hunt a lot of sea cows to bring them to extinction.
Second, the essay supposes that the sea cow population may have become extinct because ecosystems disturbances cause a decline in kelp. But the lecturer supports that if changes happened before 1768 that affected kelp, other parts of the ecosystem also should be affected, for example, a decline of marine animals such as whales. On the contrary, there is not any report about decline of other animals. so kelp is fine which could not bring food shortage to sea cows.
Third, the article suggests that the main cause of extinction of the sea cows could have been european fur traders who came to the island after 1741. Nevertheless, the professor argues that the population of sea cows is quite small before european's arrival. Their population achieved largest before 1700, and ongoing changes happened long before 1741 when european are last to arrive. Thus, european fur traders are not the main cause.
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Grammar and spelling errors:
Line 3, column 214, Rule ID: SENT_START_CONJUNCTIVE_LINKING_ADVERB_COMMA[1]
Message: Did you forget a comma after a conjunctive/linking adverb?
Suggestion: Nonetheless,
...g and 10 tons weight which is enormous. Nonetheless the population of native Siberian peopl...
^^^^^^^^^^^
Line 5, column 404, Rule ID: UPPERCASE_SENTENCE_START
Message: This sentence does not start with an uppercase letter
Suggestion: So
... report about decline of other animals. so kelp is fine which could not bring food...
^^
Transition Words or Phrases used:
also, but, first, however, if, may, nevertheless, nonetheless, second, so, still, third, thus, for example, such as, on the contrary
Attributes: Values AverageValues Percentages(Values/AverageValues)% => Comments
Performance on Part of Speech:
To be verbs : 12.0 10.4613686534 115% => OK
Auxiliary verbs: 6.0 5.04856512141 119% => OK
Conjunction : 4.0 7.30242825607 55% => More conjunction wanted.
Relative clauses : 13.0 12.0772626932 108% => OK
Pronoun: 14.0 22.412803532 62% => OK
Preposition: 27.0 30.3222958057 89% => OK
Nominalization: 7.0 5.01324503311 140% => OK
Performance on vocabulary words:
No of characters: 1235.0 1373.03311258 90% => OK
No of words: 252.0 270.72406181 93% => More content wanted.
Chars per words: 4.90079365079 5.08290768461 96% => OK
Fourth root words length: 3.98428260373 4.04702891845 98% => OK
Word Length SD: 2.43438716451 2.5805825403 94% => OK
Unique words: 146.0 145.348785872 100% => OK
Unique words percentage: 0.579365079365 0.540411800872 107% => OK
syllable_count: 376.2 419.366225166 90% => OK
avg_syllables_per_word: 1.5 1.55342163355 97% => OK
A sentence (or a clause, phrase) starts by:
Pronoun: 1.0 3.25607064018 31% => OK
Article: 7.0 8.23620309051 85% => OK
Subordination: 0.0 1.25165562914 0% => More adverbial clause wanted.
Conjunction: 3.0 1.51434878587 198% => OK
Preposition: 1.0 2.5761589404 39% => More preposition wanted as sentence beginning.
Performance on sentences:
How many sentences: 13.0 13.0662251656 99% => OK
Sentence length: 19.0 21.2450331126 89% => OK
Sentence length SD: 36.9144220626 49.2860985944 75% => OK
Chars per sentence: 95.0 110.228320801 86% => OK
Words per sentence: 19.3846153846 21.698381199 89% => OK
Discourse Markers: 10.1538461538 7.06452816374 144% => OK
Paragraphs: 4.0 4.09492273731 98% => OK
Language errors: 2.0 4.19205298013 48% => OK
Sentences with positive sentiment : 3.0 4.33554083885 69% => OK
Sentences with negative sentiment : 3.0 4.45695364238 67% => OK
Sentences with neutral sentiment: 7.0 4.27373068433 164% => OK
What are sentences with positive/Negative/neutral sentiment?
Coherence and Cohesion:
Essay topic to essay body coherence: 0.123781642834 0.272083759551 45% => OK
Sentence topic coherence: 0.0441594609752 0.0996497079465 44% => OK
Sentence topic coherence SD: 0.0347889528856 0.0662205650399 53% => OK
Paragraph topic coherence: 0.0669891588819 0.162205337803 41% => OK
Paragraph topic coherence SD: 0.0446219931681 0.0443174109184 101% => OK
Essay readability:
automated_readability_index: 11.3 13.3589403974 85% => Automated_readability_index is low.
flesch_reading_ease: 60.65 53.8541721854 113% => OK
smog_index: 3.1 5.55761589404 56% => Smog_index is low.
flesch_kincaid_grade: 9.5 11.0289183223 86% => OK
coleman_liau_index: 11.14 12.2367328918 91% => OK
dale_chall_readability_score: 7.9 8.42419426049 94% => OK
difficult_words: 53.0 63.6247240618 83% => More difficult words wanted.
linsear_write_formula: 11.0 10.7273730684 103% => OK
gunning_fog: 9.6 10.498013245 91% => OK
text_standard: 11.0 11.2008830022 98% => OK
What are above readability scores?
---------------------
Rates: 80.0 out of 100
Scores by essay e-grader: 24.0 Out of 30
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Note: the e-grader does NOT examine the meaning of words and ideas. VIP users will receive further evaluations by advanced module of e-grader and human graders.