28.1 28.1 Life in the Life in the UniverseUniverse

Are we alone?Are we alone?

Cosmic EvolutionCosmic Evolution

History of the universeHistory of the universe ParticulateParticulate GalacticGalactic StellarStellar PlanetaryPlanetary Chemical Chemical BiologicalBiological culturalcultural

What is life?What is life? Biologists do not agree!Biologists do not agree! General characteristics of life:General characteristics of life:1.1. Can react to its environment (often heal Can react to its environment (often heal

themselves when damaged)themselves when damaged)2.2. Can grow by taking in nourishment and Can grow by taking in nourishment and

process it into energyprocess it into energy3.3. Can reproduce, passing along Can reproduce, passing along

characteristicscharacteristics4.4. Have the capacity for genetic change and Have the capacity for genetic change and

can adapt to a changing environmentcan adapt to a changing environment

Are there exceptions?Are there exceptions?

Stars react to gravity, grow, Stars react to gravity, grow, generate energy and reproduce by generate energy and reproduce by triggering the formation of new starstriggering the formation of new stars

A virus is inert until in a living cell – A virus is inert until in a living cell – here it seizes control and uses the here it seizes control and uses the cell’s genetic makeup to grow and cell’s genetic makeup to grow and reproducereproduce

Assumptions of Assumptions of MediocrityMediocrity

1.1. Because life on Earth depends on Because life on Earth depends on just a few basic molecules andjust a few basic molecules and

2.2. Because the elements that makeup Because the elements that makeup these molecules are common to all these molecules are common to all stars, andstars, and

3.3. If the laws of science we know apply If the laws of science we know apply to the entire universe, THENto the entire universe, THEN

Life must have originated Life must have originated elsewhere in the cosmoselsewhere in the cosmos..

Opposing scientific Opposing scientific viewpointsviewpoints

Life on Earth is the product of a Life on Earth is the product of a series of extremely fortunate series of extremely fortunate accidents, unlikely to have occurred accidents, unlikely to have occurred anywhere else in the universeanywhere else in the universe

Chemical EvolutionChemical Evolution Much of what we happened early on (first Much of what we happened early on (first

billion years of so) is not known. billion years of so) is not known. It has been erased by geologic activity.It has been erased by geologic activity. We believe that the early earth was barren We believe that the early earth was barren

– no like in the seas or on land.– no like in the seas or on land. The atmosphere was rich in hydrogen, The atmosphere was rich in hydrogen,

nitrogen, and carbon compounds – not nitrogen, and carbon compounds – not much oxygen.much oxygen.

Over time and as Earth cooled, ammonia, Over time and as Earth cooled, ammonia, methane, carbon dioxide and water methane, carbon dioxide and water formed.formed.

Surface of early EarthSurface of early Earth

ViolentViolent RadioactivityRadioactivity LightningLightning VolcanismVolcanism Solar UV radiationSolar UV radiation Meteorite impactsMeteorite impacts

All of these things provide early All of these things provide early energyenergy

Formation of Amino Acids Formation of Amino Acids and Nucleotide Basesand Nucleotide Bases

These are organic molecules that are These are organic molecules that are the building blocks of life as we the building blocks of life as we know it.know it.

Amino acids build proteins.Amino acids build proteins. Nucleotide bases build genes that Nucleotide bases build genes that

contain genetic information.contain genetic information.

Urey-Miller ExperimentUrey-Miller Experiment Based on the idea that complex molecules Based on the idea that complex molecules

could have evolved naturally from simpler could have evolved naturally from simpler ingredients found on the primitive Earth.ingredients found on the primitive Earth.

Idea has been around since 1920s.Idea has been around since 1920s. Urey and Miller used water, methane, Urey and Miller used water, methane,

carbon dioxide, and ammonia in an carbon dioxide, and ammonia in an experiment.experiment.

They energized it with an electrical They energized it with an electrical discharge (similar to lightening).discharge (similar to lightening).

They produced amino acids.They produced amino acids.

After Urey-MillerAfter Urey-Miller The experiment has The experiment has

been reproduced been reproduced many times, with many times, with similar results.similar results.

Scientists have also Scientists have also been able to been able to synthetically synthetically produce nucleotide produce nucleotide bases.bases.

They have not been They have not been able to produce able to produce DNADNA..

What their experiment What their experiment shows…shows…

Biological molecules can be made Biological molecules can be made from non-biological molecules.from non-biological molecules.

In more advanced experiments, In more advanced experiments, protein-like microspheres have been protein-like microspheres have been produced.produced.

While they are not living, they are While they are not living, they are similar to microspheres found in the similar to microspheres found in the fossil record.fossil record.

Interstellar OriginInterstellar Origin

Some scientists believe that the organic Some scientists believe that the organic material that combined to form the first material that combined to form the first living cells was produced in interstellar living cells was produced in interstellar space and subsequently arrived on Earth space and subsequently arrived on Earth in the form of comets, interplanetary in the form of comets, interplanetary dust, and meteors.dust, and meteors.

Large amounts of organic material have Large amounts of organic material have been detected on comets, such as Halley been detected on comets, such as Halley and Hale-Bopp.and Hale-Bopp.

They also believe that much of the water They also believe that much of the water on Earth arrived from comet collisions.on Earth arrived from comet collisions.

MeteoritesMeteorites

Many of the meteorites that survive Many of the meteorites that survive to hit the Earth also contain organic to hit the Earth also contain organic compounds, including amino acids.compounds, including amino acids.

Both meteorites and comets show Both meteorites and comets show that amino acids can survive that amino acids can survive interstellar space.interstellar space.

Interesting TimelineInteresting Timeline

Earth is 4.6 billion years old.Earth is 4.6 billion years old. That is too much time to really fathom.That is too much time to really fathom. As an analogy, let’s instead say that the As an analogy, let’s instead say that the

Earth is only 46 years old.Earth is only 46 years old. We have no record at all of the first 10 We have no record at all of the first 10

years.years. Life originated at least 35 years ago.Life originated at least 35 years ago. Only about six years ago did life begin to Only about six years ago did life begin to

flourish. flourish.

Interesting TimelineInteresting Timeline Life came ashore 4 years ago.Life came ashore 4 years ago. Plants and animals began to flourish 2 Plants and animals began to flourish 2

years ago.years ago. Dinosaurs reached their peak only 1 Dinosaurs reached their peak only 1

year ago, only to die four months later.year ago, only to die four months later. Humanlike beings only became Humanlike beings only became

predominant last week. predominant last week. The last ice age was only a few days ago.The last ice age was only a few days ago. Homo sapiens did not emerge until four Homo sapiens did not emerge until four

hours ago.hours ago.

Interesting TimelineInteresting Timeline

Agriculture was invented within the Agriculture was invented within the last hour.last hour.

The Renaissance and modern The Renaissance and modern sciences came about just three sciences came about just three minutes ago!minutes ago!