BIO 2, Lecture 2BIO 2, Lecture 2BIO 2, Lecture 2BIO 2, Lecture 2

WHAT IS LIFE?WHAT IS LIFE?THE UNIVERSE AND ITS THE UNIVERSE AND ITS

CHEMISTRYCHEMISTRY

I. What is Life?

What do all living things have in common?

How do living things differ from non-living things?

Living Things:

• Can assimilate and use energy• Can respond to the environment• Can maintain a relatively constant

internal environment• Possess an inherited information

base• Can reproduce• Are composed of one or more cells• Are highly organized

-Krogh, -Krogh, Biology: A Guide to the Natural Biology: A Guide to the Natural WorldWorld, 2004, 2004

– Life is a stream of digital information that changes over time

- Living beings are just temporary hosts (survival machines) for the information molecule (DNA)

-Richard Dawkins, -Richard Dawkins, River Out Of EdenRiver Out Of Eden, , 19951995

– Entropy (disorder) in the Universe is always increasing (“arrow of time”)

– Life is highly organized– Living things must direct a stream of

negative entropy upon themselves to create and maintain order

– Life borrows energy from the Sun (either directly or indirectly)

– Overall, however, entropy in the Universe always increases

- Erwin Schroedinger, - Erwin Schroedinger, What is Life?What is Life?, 1944, 1944

SUN’S 10 BILLION YEAR CYCLE

SUNShort wavelength photons radiated into space by the

SunHIGH ENERGY

Earth re-radiates “leftover” photons

at long wavelengthsLOW ENERGY

Photosynthetic organisms on Earth harvest high energy

photons and convert them into chemical energy in the form of

starch

ENTROPYENTROPY

• BUDDHA and the man with 84 problems

• Dr. Seuss and trying to get to Solla Sollew (where there aren’t any problems, or else just a few …)

Living Things:

•Possess an information molecule–DNA (held digitally)

•Separate self from other– Fiercely protect their DNA– Maintain order and homeostasis for their DNA

•Need energy to fight entropy– To protect and promote their DNA

•REPRODUCE “themselves”– But only as vehicles to pass on the DNA they

host

•EVOLVE by natural selection (of the DNA)– Because… replication of the molecule is imperfect

II. The Universe and its Chemistry

What conditions are necessary for life?

How did those conditions arise?

In order to arise from non-living matter, life requires ...

•Space, time, and matter•Certain key elements: hydrogen, oxygen, and carbon•A stable energy source•A relatively stable environment (home)

Space, Time, and MatterThe prevailing scientific theory is that the Universe began with a huge explosion ~ 13.7 billion years ago (The Big Bang Theory)

• Time, space, and matter ALL came into existence with this event

• Since then, time and space have been expanding

• BUT ... the Universe is not expanding into anything! All we can really say is that space and time are both increasing…

~ 300,000 years after the Big Bang, protons captured electrons to form the first simple atoms

– Hydrogen (H) is the simplest element: one proton (and usually no neutrons)

– Helium (He) is the next simplest: 2 protons (and usually two neutrons)

– A small amount of Lithium (Li) and Beryllium (Be) atoms also formed soon after the Big Bang

– All elements with higher molecular weights were created later, due to nuclear fusion in the cores of stars or via supernova explosions of massive stars

A PERIODIC TABLE OF THE ELEMENTS

~ 600 million years after the Big Bang, the ‘first generation’ of hydrogen and helium gas clouds fell together by gravity to form the first stars

– Early stars were comprised entirely of H and He (with traces of Li and Be) and had no rocky planets

– They might have had gaseous planets like our own outer planets (Jupiter, Saturn, Uranus, and Neptune)

Key Elements

Stars congregated into galaxies containing hundreds of billions of stars and stretching hundreds of thousands of light years across

As we’ve seen, stars are nuclear fusion furnaces

– H is being converted to He in the core– 4 H → 1 He, so volume drops with fusion, gravity

squeezes harder, and pressure increases – As pressure increases, temp increases, levels of

radiation increase, and star is pushed outward, maintaining its size

– When all the H is used up, massive stars will begin to convert He to C (carbon) and other elements that are needed for life

Small stars: The smallest stars only convert hydrogen into helium.

Medium-sized stars: Late in their lives, when the hydrogen becomes depleted, will begin to convert helium into carbon and oxygen.

Massive stars (greater than five times the mass of our Sun): Convert helium atoms into carbon and oxygen, followed by the fusion of carbon and oxygen into neon, sodium, magnesium, sulfur and silicon. Later reactions transform these elements into calcium, iron, nickel, chromium, copper and others.

Up to the element iron (Fe), fusion releases energy. After iron, fusion requires energy.

– When the core of a massive star turns to iron, gravity can no longer be “stopped”

– A sudden and massive collapse of the core creates a neutron star or black hole where the core of the star had once been

The implosion is accompanied by a massive explosion that fuses elements heavier than iron and scatters all of the elements into space

~ 5 billion years ago, our star, the Sun, formed out of a cloud of H and He “contaminated” with the heavier elements produced by the supernova of another star

The Sun is a medium-sized star -Has been fusing hydrogen to helium for 5

billion years-Will continue for several more billion years-If our Sun was much larger, it would have

“burned out” before live evolved

A Stable Energy Source

In the Nebular Theory for the formation of the solar system, a slowly rotating cloud of gas and dust collapsed by gravity and began to spin faster because of the conservation of angular momentum

A Home

The collapsing, spinning nebula began to flatten into a rotating pancake

As the nebula collapsed further, local regions began to contract gravitationally on their own because of instabilities in the collapsing, rotating cloud

• The Moon probably formed as a result of an early catastrophic collision between Earth and another planetoid, which also created the tilt in Earth’s axis

• The heat of early bombardments and impacts kept Earth hot and enabled heavier elements (principally iron) to flow to the core, where they remained molten

• Over time, the crust of the Earth cooled and became solid (a home for life)– Importance of the magnetic field for

holding an atmosphere– Water

• Earth’s early atmosphere consisted of:

• Nitrogen and its oxides• Water vapor (huge amounts; later

condensed into oceans• Carbon dioxide and carbon monoxide• Methane• Sulfur dioxide• Hydrogen sulfide and hydrogen

cyanide• Virtually no oxygen

• Lots of volcanic activity

• Comet and asteroid bombardments until about 3.9 billion years ago

“No intelligent life forms here, Captain. Beam

me up!”