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Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent suns To a destination where all signs tell us It is possible and imperative that we learn A brave and startling truth. — Maya Angelou
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Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Dec 19, 2015

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Page 1: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Chapter 18Life in the Universe

We, this people, on a small and lonely planetTraveling through casual spacePast aloof stars, across the way of indifferent sunsTo a destination where all signs tell usIt is possible and imperative that we learnA brave and startling truth.

— Maya Angelou

Page 2: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

18.1 Life on Earth

Our goals for learning• When did life arise on Earth? • How did life arise on Earth?• What are the necessities of life?

Page 3: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

When did life arise on Earth?

• Probably before 3.85 billion years ago. When was our planet formed?

• Shortly after end of heavy bombardment, 4.2-3.9 billion years ago.

Page 4: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Fossils are relics of organisms that died long ago. They accumulate at the bottom of the seas where they get compressed by the weight of upper layers, into rock.

Erosion or tectonic activity can later expose those fossils…

Fossil evidence…

The rock layers of the Grand Canyon record 2 billion years of Earth’s history…

Page 5: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Fossil evidence for microbes 3.5 billion years ago• Already fairly complex life (photosynthesis), suggesting much earlier origin.• Carbon isotope evidence pushes origin to before 3.85 billion years ago.

Colonies of microbes from Western Australia. Old samples show that microbes were present even 3.5 billion

years ago.

Page 6: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

The Geological Time Scale

Life formed relatively fast!

Page 7: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

How did life arise on Earth?

• All life on Earth shares a common ancestry.

• We may never know exactly how the first organism arose, but laboratory experiments suggest plausible scenarios.

• Life evolves through time.

Page 8: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

The Theory of Evolution

• The fossil record shows that evolution has occurred through time.

• Darwin’s theory tells us HOW evolution occurs: through natural selection.

• Theory supported by discovery of DNA: evolution proceeds through mutations.

Page 9: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

• Mapping genetic relationships has led biologists to discover this new “tree of life.”• Plants and animals are a small part of the tree. • Suggests likely characteristics of common ancestor

Page 10: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

• These genetic studies suggest that the earliest life on Earth may have resembled the bacteria today found near deep ocean volcanic vents (black smokers) and geothermal hot springs .

A volcanic vent on the ocean floor that spews out hot (110C, 230F) mineral rich water.

Aerial photo of a hot spring in Yellowstone. Different colors are from different microbes.

Page 11: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Laboratory experiments allow us to investigate possible pathways to the origin of life.

Miller-Urey experiment (and more recent experiments):• Building blocks of life form easily and

spontaneously under conditions of early Earth (essentially mix chemicals and spark them with energy).

Page 12: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Microscopic, enclosed membranes or “pre-cells” have been created in the lab.Also, long strands of RNA, the code of life which came before DNA, has

been artificially created.

Enclosed membranes that self-assamble in experiments mimicking conditions on the early Earth.

Page 13: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Chemicals to Life?

Maybe this is how it happened…

Page 14: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Could life have migrated to Earth?

• Venus, Earth, Mars have exchanged tons of rock (blasted into orbit by impacts)

• Some microbes can survive years in space...

Page 15: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Brief History of Life

• 4.4 billion years - early oceans form• 3.5 billion years - cyanobacteria start releasing

oxygen.• 2.0 billion years - oxygen begins building up in

atmosphere (before that, all oxygen was pulled out of the atmosphere by chemical reaction with rocks)

• 540-500 million years - Cambrian Explosion• 225-65 million years - dinosaurs and small mammals

(dinosaurs ruled)• Few million years - earliest hominids

Page 16: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

The Geological Time Scale

Life formed relatively fast!

Our atmosphere formed.

Page 17: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Thought QuestionYou have a time machine with a dial that you can spin to send you randomly to any time in Earth’s history. If you spin the dial, travel through time, and walk out, what is most likely to happen to you?

A. You’ll be eaten by dinosaurs.B. You’ll suffocate because you’ll be unable to

breathe the air.C. You’ll be consumed by toxic bacteria.D. Nothing: you’ll probably be just fine.

Page 18: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Thought QuestionYou have a time machine with a dial that you can spin to send you randomly to any time in Earth’s history. If you spin the dial, travel through time, and walk out, what is most likely to happen to you?

A. You’ll be eaten by dinosaurs.B. You’ll suffocate because you’ll be unable to

breathe the air.C. You’ll be consumed by toxic bacteria.D. Nothing: you’ll probably be just fine.

Page 19: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

What are the necessities of life?

• Nutrient source

• Energy (sunlight, chemical reactions, internal heat)

• Liquid water (or possibly some other liquid)

Hardest to find on other planets

Page 20: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

What have we learned?

• When did life arise on Earth?• Fossil evidence puts the origin of life at least 3.5

billion years ago, and carbon isotope evidence pushes this date to more than 3.85 billion years ago. Thus, life arose within a few hundred million years after the last major impact of the heavy bombardment, and possibly in a much shorter time.

Page 21: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

What have we learned?• How did life arise on Earth?• Genetic evidence suggests that all

life on Earth evolved from a common ancestor, and this ancestor was probably similar to microbes that live today in hot water near undersea volcanic vents or hot springs. We do not know how this first organism arose, but laboratory experiments suggest that it may have been the result of natural chemical processes on the early Earth.

Page 22: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

What have we learned?

• What are the necessities of life?

• Life on Earth thrives in a wide range of environments, and in general seems to require only three things: a source of nutrients, a source of energy, and liquid water.

Page 23: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

18.2 Life in the Solar System

Our goals for learning• Could there be life on Mars? • Could there be life on Europa or other jovian

moons?

Page 24: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Could there be life on Mars?• Mars had liquid water in the distant past• Still has subsurface ice; possibly subsurface water near sources of volcanic heat. Is Mars still geologically active?

Page 25: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

In 2004, NASA Spirit and Opportunity Rovers sent home new mineral evidence of past liquid water on Mars.

Page 26: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Close-up view of rock apparently formed in water.

Page 27: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

The Martian Meteorite debate

composition indicates origin on Mars.

• 1984: meteorite ALH84001 found in Antarctica • 13,000 years ago: fell to Earth in Antarctica• 16 million years ago: blasted from surface of Mars• 4.5 billion years ago: rock formed on Mars

Page 28: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

• Does the meteorite contain fossil evidence of life on Mars?

Picture show the meteorite from Mars (left) and rock from the Earth. Structure on Earth was formed by nanobacteria, and resembles the one from Mars. But meteorite was probably contaminated while on Antarctica.

Page 29: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Could there be life on Europa or other jovian moons?

Page 30: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

• Ganymede, Callisto also show some evidence for subsurface oceans.

• Relatively little energy available for life, but still…

• Intriguing prospect of THREE potential homes for life around Jupiter alone…

Ganymede Callisto

Page 31: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Titan

• Surface too cold for liquid water (but deep underground?)• Liquid ethane/methane on surface!• Huygens probe descent, Jan. 2005

Page 32: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

What have we learned?

• Could there be life on Mars?

• Mars once had conditions that may have been conducive to an origin of life. If life arose, it might still survive in pockets of liquid water underground.

Page 33: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

What have we learned?

• Could there be life on Europa or other jovian moons?

• Europa probably has a subsurface ocean of liquid water, and may have undersea volcanoes on its ocean floor. If so, it has conditions much like those in which life on Earth probably arose, making it a good candidate for life beyond Earth. Ganymede and Callisto might have oceans as well. Titan may have other liquids on its surface, though it is too cold for liquid water. Perhaps life can survive in these other liquids, or perhaps Titan has liquid water deep underground.

Page 34: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

18.3 Life Around Other Stars

Our goals for learning• Are habitable planets likely?• Are Earth-like planets rare or common?

Page 35: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Are habitable planets likely?

Caveat: Telescopically we can search only for planets with habitable surfaces — not for worlds with Europa-like subsurface oceans.

Definition:

A habitable world contains the basic necessities for life as we know it, including liquid water.

• It does not necessarily have life.

Page 36: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Constraints on star systems:

1) Old enough to allow time for evolution (rules out high-mass stars - 1%)

2) Need to have stable orbits (might rule out binary/multiple star systems - 50%)

3) Size of “habitable zone”: region in which a planet of the right size could have liquid water on its surface.

Even so… billions of stars in the Milky Way seem at least to offer the possibility of habitable worlds.

Page 37: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

The more massive the star, the larger the habitable zone — higher probability of a planet in this zone.

Page 38: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Finding them will be hard

Recall our scale model solar system:

• Looking for an Earthlike planet around a nearby star is like standing on the East Coast of the United States and looking for a pinhead on the West Coast — with a VERY bright grapefruit nearby.

• But new technologies should soon show the way…

Page 39: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

• Kepler (2007 launch) will monitor 100,000 stars for transit events for 4 years.

Later: SIM (2009?), TPF (2015?): interferometers to obtain spectra and crude images of Earth-size planets.

Page 40: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Spectral signatures of life

oxygen/ozone

Earth

Venus

Mars

Page 41: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Are Earth-like planets rare or common?

• Galactic “habitable zone”: minimum limits on heavy element abundance, distance from galactic center?

• Jupiter protection from frequent impacts?

• Climate stabilized by a large Moon and plate tectonics?

We don’t yet know how important or negligible these concerns are.

Page 42: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

What have we learned?• Are habitable planets likely?• Billions of stars have at least moderatesize habitable

zones in which life bearing planets might exist. We do not yet have the technology to search for habitable planets directly, but several planned missions should be able to begin the search soon.

Page 43: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

What have we learned?

• Are Earth-like planets rare or common?

• We don’t know. Arguments can be made on both sides of the question, and we lack the data to determine their validity at present.

Page 44: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

18.4 The Search for Extraterrestrial Intelligence

Our goals for learning• How many civilizations are out there?• How does SETI work?

Page 45: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

The Drake Equation

Number of civilizations with whom we could potentially communicate

= NHP flife fciv fnow

NHP = total # of habitable planets in galaxy

flife = fraction of habitable planets with life

fciv = fraction of life-bearing planets w/ civilization at some time

fnow = fraction of civilizations around now.

How many civilizations are out there?

Page 46: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

We do not know the values for the Drake Equation

NHP : probably billions.

flife : ??? Hard to say (near 0 or near 1)

fciv : ??? It took 4 billion years on Earth

fnow : ??? Can civilizations survive long-term?

Page 47: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Are we “off the chart” smart?

Page 48: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Current SETI efforts could not detect signals as weak as our own radio/TV broadcasts. For now, at least, we are looking for deliberately broadcast signals..

How does SETI work?

Page 49: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

We’ve even sent a few signals ourselves…

Earth to globular cluster M13: Hoping we’ll hearback in about 42,000 years!

Page 50: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Your computer can help! SETI @ Home: a screensaver with a purpose.

SETI@home is a scientific experiment that uses Internet-connected computers in the Search for Extraterrestrial Intelligence (SETI). You can participate by

running a free program that downloads and analyzes radio telescope data.

Page 51: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

What have we learned?• How many civilizations are out there?• We don’t know, but the Drake equation gives us a

way to organize our thinking about the question. The equation (in a modified form) says that the number of civilizations in the Milky Way Galaxy with whom we could potentially communicate is where is the number of habitable planets in the galaxy, is the fraction of habitable planets that actually have life on them, is the fraction of life-bearing planets upon which a civilization capable of interstellar communication has at some time arisen, and is the fraction of all these civilizations that exist now.

Page 52: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

What have we learned?

• How does SETI work?• SETI, the search for

extraterrestrial intelligence, generally refers to efforts to detect signals—such as radio or laser communications—coming from civilizations on other worlds.

Page 53: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

18.5 Interstellar Travel and Its Implications to Civilization

Our goals for learning• How difficult is interstellar travel?• Where are the aliens?

Page 54: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

How difficult is interstellar travel?

• Very!

• Current spacecraft travel at <1/10,000 c; 100,000 years to the nearest stars.

Pioneer plaque Voyager record

Page 55: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Real interstellar travel faces huge hurdles:

• Far more efficient engines• Incredible energy requirements• Ordinary particles become dangerous cosmic rays• Time dilation affects crew

Page 56: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Where are the aliens?

“Fermi’s Paradox”• Plausible arguments suggest that civilizations should be

common, for example:• Even if only 1 in 1 million stars gets a civilization at some

time 100,000 civilizations• Moreover, most of the stars are older than our Sun, so

other civilizations had several extra billion years to develop. They should have already occupied the Galaxy!

• So why we haven’t we detected them?

Page 57: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Possible solutions to the paradox

1) We are alone: life/civilizations much rarer than we might have guessed.

• Our own planet/civilization looks all the more precious…

Page 58: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Possible solutions to the paradox

2) Civilizations are common but interstellar travel is not. Perhaps because: Interstellar travel more difficult than we think. Desire to explore is rare. Civilizations destroy themselves before achieving

interstellar travel

These are all possibilities, but not very appealing…

Page 59: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Possible solutions to the paradox

3) There IS a galactic civilization…

… and some day we’ll meet them…

Page 60: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

What have we learned?• How difficult is interstellar

travel?• Convenient interstellar travel

remains well beyond our technological capabilities, because of the technological requirements for engines, the enormous energy needed to accelerate spacecraft to speeds near the speed of light, and the difficulties of shielding the crew from radiation. Nevertheless, it seems reasonable to think that we will someday achieve interstellar travel if we survive long enough.

Page 61: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

What have we learned?

• Where are the aliens?• It seems that we should be capable of colonizing the

galaxy in a few million years or less, and the galaxy was around for at least 7 billion years before Earth was even born. Thus, it seems that someone should have colonized the galaxy long ago—yet we have no evidence of other civilizations. Every possible category of explanation for this surprising fact has astonishing implications for our species and our place in the universe.

Page 62: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Which of the following best describes the predominant scientific view of the origin of life on Earth? [Hint]

  A. Life probably migrated to Earth from some other world.

  B. Life arose through a series of extremely unlikely chemical coincidences, making it seem almost miraculous that life ever came to exist at all.

  C. We may never know precisely how life arose on Earth, but current knowledge suggests that life likely arose easily under the conditions that prevailed on the early Earth.

  D. We can describe with great certainty the precise steps by which life arose on Earth.

Page 63: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

When we analyze whether a world is a possible home to life, the key thing we look for is _________. [Hint]

  A. surface coloration changes that could indicate vegetative growth

  B. the presence of organic molecules such as amino acids

  C. evidence of atmospheric oxygen

  D. the past or present existence of liquid water

Page 64: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

We are not yet capable of detecting life on planets around other stars. But as our technology develops, our first real chance of detecting such life will probably come from _________. [Hint]

  A. examining high-resolution images of the planets made by orbiting telescopes

  B. determining the orbital properties of the planets

  C. examining spectral lines from the atmospheres of distant planets

  D. sending spacecraft to study the planets up close

Page 65: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Which of the following describes a major danger of interstellar travel at near-light speed? [Hint]

  A. Asteroid fields floating in interstellar space will present a navigational challenge.

  B. Atoms and ions in interstellar space will hit a fast-moving spacecraft like a flood of dangerous cosmic rays.

  C. Any interstellar journey will take much longer than the lives of the crew members.

  D. Time dilation will slow the heart beats of the crew to a dangerously low rate.

Page 66: Chapter 18 Life in the Universe We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent.

Which of the following is NOT considered a potential solution to the question of why we lack any evidence of a galactic civilization? [Hint]

  A. There is no galactic civilization because we are the first species ever to achieve the ability to study the universe.

  B. The galactic civilization probably is undetectable because they operate under different laws of physics from the ones we know.

  C. There is no galactic civilization because all civilizations destroy themselves before they achieve the ability to colonize the galaxy.

  D. The galactic civilization is deliberately avoiding contact with us.


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