Transcript BIO 10 Lecture 2

BIO 10
Lecture 2
THE UNIVERSE AND ITS
CHEMISTRY: WHAT IS LIFE?
Setting the Stage for Life
The prevailing scientific theory for how the
Universe came into being (i.e. the theory that
explains the most facts and has the best predictive
power) is that the Universe began with a Big Bang
explosion ~ 13.7 billion years ago.
•Time, space, and matter came into existence
with this event
•Since an act of creation implies space and time,
most scientists do not believe it is even
meaningful to talk about a Creator or Creation
Event
•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 hydrogen
atoms.
• Hydrogen (H) is the simplest element; it has
only one proton and one electron
• The Big Bang also created a small amount of
Helium (He), Lithium (Li) and Beryllium (Be)
• All elements with higher molecular weights
were created later, in the bellies of massive
stars
A PERIODIC TABLE OF THE ELEMENTS
• ~600 million years after the Big Bang, the
‘first generation’ of galaxies and stars fell
together by gravity
• 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)
• Stars are nuclear fusion furnaces
– H is being converted to He in the core
– 4 H → 1 He, so pressure drops with fusion
and gravity squeezes harder
– As gravity increases, temp increases, levels
of radiation increase, and star is pushed
outward, maintains size
– When all the H is used up, the star will begin
to convert He to C (carbon), the most
important element for life
Small stars: The smallest stars only convert
hydrogen into helium.
Medium-sized stars (like our Sun): Late in their
lives, when the hydrogen becomes depleted, will
begin to convert helium into oxygen and carbon.
Massive stars (greater than five times the mass of
ourSun): When their hydrogen becomes depleted,
high mass stars 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 iron (Fe), fusion creates 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 implosion 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 beyond iron
and scatters heavy 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
• ~ 4.5 billion years ago, The Earth formed
from the same spinning disk that formed the
Sun.
• Metals and other heavy elements remained
closer to the sun; gaseous planets like Jupiter
and Saturn formed farther out
• Thus, the solar system, and particularly
the inner planets in the solar system,
were rich in heavier elements
• The chemistry of life relies mostly on
the following elements:
» Hydrogen
» Carbon
» Oxygen
» Nitrogen
» Phosphorous
Created in
supernovas
From Muck to Microbes
• Formation of the Solar System
– The oldest rocks on are just slightly younger than the sun:
4.5 billion years old
• Nebular Hypothesis: The solar system was born
out of a swirling (rotating) cloud of hydrogen and
helium, with a smattering of heavier elements
– Most of the H and He are found in the sun; rocky planets
made of heavier elements (like Earth) are found close to
the sun, while gaseous planets (Jupiter, Saturn, Uranus,
Neptune) are found further out
• Earth formed as an accretion of smaller “asteroidlike” bodies
In the Nebular Hypothesis, a cloud of gas and dust
collapsed by gravity begins to spin faster because
of the conservation of angular momentum
The collapsing, spinning nebula begins to flatten
into a rotating pancake
As the nebula collapses further, local
regions begin to contract gravitationally on
their own because of instabilities in the
collapsing, rotating cloud
• The Moon 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
• The Nebular Hypothesis is considered to be
a good scientific theory because it explains
many facts about the solar system
– All of the planets revolve around the sun in the
same direction
– the axes of most planets are at right angles to
their plane of orbit
– all the planets revolve around the sun in roughly
the same plane
– All evidence to date suggests that the planets
and sun are roughly the same age
Earth’s Early Environment
• Molecules present on early Earth included nitrogen,
water vapor, and carbon dioxide – the same gases
currently produced by volcanoes
• Other minor contributors included methane,
ammonia, carbon monoxide, sulfur dioxide, and
hydrogen cyanide – NO OXYGEN!
• Comet impacts may have contributed large amounts
of water vapor, helping to form the early oceans
• Earth’s age can be estimated from levels of
radioactive 238U versus 206Pb in rocks, and the age
of the Moon can be accurately determined using this
method
What is Life?
• What is Life?
• In-class Exercise:
– How is life distinguished from non-life?
How do we know that something is
ALIVE?
Some Definitions for Life
• Krogh (2004)
– Living things:
• Can assimilate and use energy
• Can respond to the environment
• Can maintain a relatively constant internal
environment
• Possesses an inherited information base
• Can reproduce
• Are composed of one or more cells
• Are highly organized
• Dawkins (1995)
– Living things are the survival machines
for a stream of digital information that
changes over time
– Living beings are just temporary hosts for
the information molecule (DNA) and exist
for the sole purpose of enabling that
molecule to be perpetuated
– DNA is ultimately the only thing that
survives through time
• Schroedinger (1944)
– Life directs a stream of negative entropy
upon itself to create order from chaos
– Entropy (disorder) in the Universe is
always increasing
– Life works against entropy by borrowing
energy from the Sun
– In the end, however, entropy always wins
• 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 …)
Short Review of Lecture 2
• What is the best current scientific theory for
the origin of the Universe?
• Why does the Big Bang theory make the idea
of a "Creator" or "Creation Event" a
meaningless thing to discuss?
• What is space expanding into?
• What elements were formed in the Big Bang?
• How were other (heavier) elements (including
carbon, the basis for life chemistry) formed?
• What are the common characteristics shared
by all living things but not by non-living
things?