首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
What does the professor imply about the asteroid impact?
What does the professor imply about the asteroid impact?
admin
2012-01-14
63
问题
What does the professor imply about the asteroid impact?
[Professor (female)] Class, let’s jump right into the lecture for today. Q7 Let me start by telling you
an interesting fact that’s relevant to the rest of the lecture: the energy released
by the impact of a large asteroid on our planet is equivalent to several million
nuclear weapons. Tell me, why is this information important--from a historical
perspective?
[Student A (male)] Well, if an impact like that can release as much energy as--as millions of nuclear
weapons...well,Q7 that’s catastrophic enough to explain extinction events in
Earth’s history.
[Professor] Exactly. Now by "extinction events" we’re referring to periods in the planet’s
history when there’s a very...a very marked decrease in the number of species.
Um, and it happens within a relatively short period of time--at least on a
geological timescale. There’ve been a handful of extinction events during
the past 540 million years, but--but the one that’s, um, generated the most
interest--because it killed the dinosaurs--um, it’s the most recent one, the K-T
extinction event...which happened 65 million years ago.
[Student B (female)] Q8 [Professor], what does "K-T" mean?
[Professor] Oh, "K-T." Well, "K" is a standard abbreviation for the Cretaceous Period. And
"T" is the standard abbreviation for the Tertiary Period. Does anyone want to
take a guess, then, about the meaning of the name "K-T"?
[Student A] Does it mean the extinction event occurred, um, during the Cretaceous and
Tertiary Periods?
[Professor] Sort of. Of course, we aren’t exactly sure how long the K-T extinction event
lasted.’Could’ve been a few years...could’ve been a few thousand years...or
could’ve been even longer. But for a general figure, we date the K-T extinction
event to around the end of the Cretaceous Period and the beginning of the
Tertiary Period. It’s basically seen as the dividing line between the two. And
Q6 what we’re going to talk about today is the reason why this extinction
event happened. Which goes back to what I mentioned earlier--asteroid
impacts can be extremely destructive.
Uh, before I go on, Q11 I just want to emphasize that no one knows what
caused the K-T extinction event...and there’re many hypotheses. The asteroid
hypothesis is of course just one of many. Could’ve been volcanic activity,
climate change, or sea-level changes...just to name a few theories.
But, anyway, let’s get back to the asteroid hypothesis. OK. Now even before
there was any, um, evidence for an asteroid impact causing mass extinctions,
um, people were talking about the possibility. In 1980, though, we got our
first glimpse of evidence that really backed the idea of an asteroid causing--
causing the K-T extinction event. A group of researchers led by Luis Alverez
discovered an interesting, um, stripe...uh, in the sedimentary layers of Earth’s
crust that date back to the end of the Cretaceous Period and the beginning of
the Tertiary Period. At the boundary of these two, um, layers--we call it the K-T
boundary--there were deposits of a very rare element: iridium. Alverez and his
team discovered that, um, the stripe of iridium was global...it appeared at the
K-T boundary in sedimentary layers all over the world. Alverez and his team
wondered about the cause of the iridium deposits and, um, suggested that the
iridium might have been the result of an asteroid impact that occurred around
that time.
The theory was based on the fact that, uh, that certain types of asteroids contain
a percentage of, um, iridium. So the Alvarez team made some calculations...
assuming that the K-T asteroid had the, um, the usual amount of iridium. They
came up with a size for the hypothetical asteroid--ten kilometers in diameter.
That’s about the size of Manhattan. An asteroid that size would’ve hit Earth with
a force about 2 million times greater than the most powerful bomb ever tested
by humans! Unimaginable.
[Student B] That blast would’ve immediately killed life all over the planet?
[Professor] Well, not exactly like that. Q9(C)Q10 There’d be a huge dust cloud
that would actually’ it would actually block out sunlight and prevent
photosynthesis from happening on the surface of the planet. Bad news
for plants...and for everything that eats plants...and for everything that eats
things that eat plants, Q9(D) There also might’ve been, um, global firestorms.
Produced by--by flaming debris from the blast. And if there were widespread
fires, well, Q9(A) there would’ve been a lot of CO2 in the atmosphere...um, and
as a result--a temporary greenhouse effect. So, um, some of the species that
survived the initial blast would’ve been killed off by all that.
[Student A] Q11 An asteroid impact like that would’ve made a pretty huge dent
in the Earth, wouldn’t it? I mean, is there any evidence of a crater from the K-T
asteroid?
[Professor] Actually, there is. It’s on Mexico’s Yucatan coast. So there’s certainly a lot of
evidence supporting the asteroid theory of the K-T extinctions. Still--no one
knows for sure.
选项
A、It is a widely accepted theory, but not scientifically proven yet.
B、Scientists disagree about the size of the asteroid that hit the planet.
C、It is something which he does not believe in personally.
D、It is less fully researched than other theories.
答案
A
解析
转载请注明原文地址:https://kaotiyun.com/show/yFyO777K
0
托福(TOEFL)
相关试题推荐
Choosethecorrectletter,A,B,CorD.Writeyouranswersinboxes37-40onyouranswersheet.Duringtheearlymodernera,a
Youshouldspendabout20minutesonQuestions14-26whicharebasedonReadingPassage2below.TheConquestofMalariainItal
AncientPeopleinSaharaOnOct.13,2000,PaulSereno,aprofessorfromtheUniversityofChicago,guidedateamofpalaeon
AccordingtoMrSingh,onwhichthingdomanypeoplemakesuperficialobservations?AccordingtoMrSingh,thebiggestproblem
PrairieDogbarkshave______meanings.PrairieDogsinArizonaandColoradoappeartospeakdifferent,butmutually-comprehens
Theuniversityhasproduceda______toinformstudentsaboutthedifferentaccommodationoptionsavailable.MalvernHalls
TheprofessoralreadyknowssomethingaboutClarefromher______.
CompletethenotesinNOMORETHANTHREEWORDS.ThesubjectstakenInthefirstsemesterinthiscoursearepsychology,sociolog
Accordingtothepassage,anorganismwithouthardbodypartsItcanbeinferredthatfloodplains,deltas,andstreamchannel
Tunas(migratelong)distancesoveralltheworld’s(oceans)andoccupy(tropical),temperate,andeven(some)thecoolerwaters
随机试题
美国文官制度的基本法是()
设y=y(x)由方程1—y+xxy=0确定,求
女,25岁,口服乐果40ml入院。神清,经洗胃和阿托品56mg治疗后瞳孔散大,烦躁,皮肤潮红,心率136次/分,肺部仍有散在湿啰音,有尿潴留。下列哪项措施最重要
以下能拉动内需促进经济增长的行为有()。
人类珍贵的文化传统,绵延久远,力道强劲,就像是这个世界上永恒的生命。它以很长的周期、有时甚至长过某代人一生的频度在__________着。它不会__________,即使有时候看不到了,也还在地底下扎着根、生长着,伺机而发。填入划横线部分最恰当的一项是:
限制民事行为能力人订立的合同,相对人可以催告法定代理人在1个月内予以追认。1个月的追认期满,法定代理人仍未做出表示的,则()。
A.位于鼻唇沟B.位于前额和颞部C.位于舌颌沟D.位于上唇及下唇E.无“扳机点”三叉神经痛位于第1支,“扳机点”可能()。
在显存中,表示黑白图像的像素点最少需(1)位。彩色图像可以用(2)三基色表示。
主题数据库是一类重要的数据环境,以下是关于数据环境特点的描述。Ⅰ.简单、容易实现Ⅱ.具有较低的维护成本Ⅲ.提高了应用开发效率Ⅳ.与应用项目对应Ⅴ.独立于应用项目其中属于主题数据库优点的是
John,lookatthetime.______youplaythepianoatsuchalatehour?
最新回复
(
0
)