Download Earth and Space Science

(6) Earth in space and time. The student
knows the evidence for how Earth's
atmospheres, hydrosphere, and geosphere
formed and changed through time. The
student is expected to:
(C) investigate how the formation of
atmospheric oxygen and the ozone layer
impacted the formation of the geosphere and
biosphere; and
(D) evaluate the evidence that Earth's cooling
led to tectonic activity, resulting in continents
and ocean basins.
The geosphere
refers to
everything, from
the core of the
Earth to its surface.
As you can see,
there are many
features within the
Earth, many of
which we already
have learned about.
The biosphere is the
layer of life on Earth. It
exists beneath, upon, and
above the surface in the
atmosphere as well.
Axolotl
Soil Nematodes
Airborne Bacteria
Harvestman
One thing most
geologists agree on is
that the Earth’s first
atmosphere contained
no free oxygen. There
were trace amounts of
Oxygen bound in water
molecules, and Carbon
dioxide…but none of it
was “free”, or
molecular oxygen. (O2)
Photochemical Dissociation Hypothesis states that the Sun’s
energy helped the atmosphere evolve through the following
processes:
•
The UV light combined with water vapor to set the hydrogen off
into space and freeOxygen
the oxygen.
2H2O + UV light energy
2H2 (freed into space) + O2
Oxygen
• The newly freed oxygen
reacted with methane, forming carbon
dioxide and additional
water vapor.
+
+
CH4 + 2O2
CO2 + H2O
Oxygen
• The oxygen also reacted with ammonia, producing nitrogen and
water.
4NH3 + 3O2
2N2 + 6H2O
• After converting the ammonia and methane to carbon dioxide and
nitrogen, free oxygen began to accumulate as further dissociation
of water vapor continued.
This theory states that our atmosphere was
delivered to us from the Earth’s interior through
volcanic eruptions.
In contrast to the Photochemical Dissociation
Hypothesis, the Outgassing Hypothesis argues that
the free oxygen came from the photosynthesis of
primitive organisms which existed 1.5 - 3.5 billion
years ago.
The oxygen took approximately 2 billion years to
become free, but when it did, it formed the ozone
layer, within Earth’s stratosphere, eliminating the
dangerous radiation and setting up the foundation for
a habitable planet. Without ozone, life would not have
been possible.
It is obvious that Earth
contains O2 now, and without
it, aerobic life would not be
possible.
What life could have evolved
all those billions of years ago,
before there was significant
O2 in our atmosphere?
Anaerobic life forms
http://www.teachersdomain.
org/resource/tdc02.sci.life.ce
ll.stetteroxygen/
1. How is the geosphere different from the biosphere?
2. Describe how photochemical dissociation could have freed
oxygen.
3. What other molecules did free O2 interact with to create
water?
4. Oxygen reacts with _______ , a part of volcanic
outgassing, to produce nitrogen gas in our atmosphere.
5. Outgassing hypothesis states our oxygen came from
__________, due to all the CO2 generated by volcanoes.
6. Where does ozone form a protective barrier in our
atmosphere?
7. What type of life evolved first, and is killed in the
presence of O2?
Although the early Earth was mostly
devoid of molecular oxygen, high
volcanic activity released significant
amounts of molecular hydrogen.
With little oxygen available to
convert that hydrogen into water,
hydrogen gas probably accumulated
in the atmosphere and oceans in
concentrations as high as hundreds
to thousands of parts per million.
The evolution of O2 in our
atmosphere spelled doom
Thus, the early Earth was likely a
for the proliferate
paradise for methanogens
methanogens, and other
(methane-producing) that fed
types of extremophiles that
directly on hydrogen and carbon
had evolved during this early
dioxide, at least until the
period in Earth’s past. Once
atmospheric hydrogen was depleted.
again…this was the GOE.
Despite their small stature, one
of the first aerobic organisms
(require the presence of O2)
set in motion a process that
would change everything.
These cyanobacteria (also
known as blue-green algae),
were remarkably selfsufficient creatures that could
use the sun’s energy to make
their own food, and fix
While this may not seem significant, the cycling of nitrogen on
nitrogen, a process where
Earth is essential for life. It is found in amino acids, proteins,
nitrogen gas is converted into
and genetic material. Nitrogen is the most abundant element in
ammonia or nitrate.
the atmosphere (~78%). However, gaseous nitrogen must be
'fixed' into another form so that it can be used by living
organisms. Because cyanobacteria were the first
photosynthetic organisms, they are also responsible for
getting the cycling of carbon and oxygen going too!
And then...nothing else happened. At
least, not for another two billion
years!
It wouldn't be until about 600 million
years ago, that the first multicellular
organisms finally emerged.
So what happened during that
immense, multi-billion year gap? Why
did it take so long for more complex
life to arrive on the scene? For that
matter, why did oxygen suddenly spike
2.5 billion years ago? The spike was
very likely due to photosynthesis, but
as to why complex life took so long…
The simple, uncomfortable answer is
that we don't really know.
???
Formation of Silicates:
BIFs and Red Beds:
Oxygen combines
Without
oxygen inwith
the silicon
atmosphere,
in various
neither of these
would have evertoexisted
configurations
create on
80%
ourofplanet.
the Earth’s
lithosphere…a silicate material.
8. What anaerobic organisms used hydrogen in
chemosynthesis to produce food?
9. What are cyanobacteria?
10. Why were cyanobacteria so important to
the nitrogen cycle?
Carbon and oxygen
cycles?
11. Why did O2 spike in the atmosphere 2.5
billion years ago?
12. How did oxygen influence the geosphere?
We already know that over time, the Earth’s
crust cooled. The crust is thin, varying from a
few tens of kilometers thick beneath the
continents to less than 10 km thick beneath
the many of the oceans.
The crust and upper mantle together constitute
the lithosphere, which is typically 50-100 km
thick and is broken into large plates. These
plates sit on the asthenosphere.
The asthenosphere is kept a plastic fluid
consistency largely through heat generated by
radioactive decay. This heat source is small,
but nevertheless, because of the insulating
properties of the Earth's rocks at the surface,
this is sufficient to keep the asthenosphere
flowing.
Thermal energy can be transferred in three ways…
 Radiation Energy transfer across the vacuum of space
 Conduction Energy transfer directly from molecule to molecule (solids)
 Convection Energy transfer through fluids (liquids and gases)
Very slow convection currents flow in the asthenosphere,
(upper portion of the mantle) and these currents provide
horizontal forces on the plates of the lithosphere much as
convection in a pan of boiling water causes a piece of cork
on the surface of the water to be pushed sideways
Of course, the timescale for
convection in the pan is seconds and
for plate tectonics is 10-100 million
years, but the principles are similar.
Differentiation
within the Earth is
crucial to plate
tectonics, because
it is responsible for
producing an
interior that can
support tectonic
motion.
It is this tectonic motion that is responsible
for the widening Atlantic Ocean, along the
divergent mid-Atlantic ridge, and the
The heat generated byconstricting
the lower mantle,
drives the
convection
currents
Pacific
Ocean,
which
is upward
against the lithospheric plates. As the currents cool, they move laterally, pushing
subducting
beneath
themove
North
and again,
South
and pulling the lithosphere
apart. Then,
the currents
downward
where
they begin to heat up once
more duetectonic
to proximity
to lower mantle heat.
American
plates.
Pangea Ultima
How did
we get
here?
https://youtu.be/C
m5giPd5Uro
Being dynamic, the Earth is still changing. 150 million years in the future,
the continents should look something like this.
In 250 million years, we will have another pangea supercontinent.
13. Where is Earth’s crust thickest?
Thinnest?
14. By what three ways can thermal energy be
transferred, and how
15. What type of energy transfer is at work in
Earth’s mantle, which drives tectonic plate
movement?
16. What is tectonic motion doing to the
Atlantic Ocean?
17. When will the next supercontinent form?