Transcript 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
 Diatomic Oxygen
 Oxygen reacts with the iron in the geosphere creating iron
oxide (rust)
 Levels of atmospheric diatomic oxygen and dissolved
diatomic oxygen influenced aerobic life.
 Stratospheric ozone protects terrestrial life from UV radiation
allowing life to flourish
(d) and 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 that we will
learn 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
1. What are some of the Earth’s
features within the geosphere?
2. What is the biosphere?
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 ultraviolet light combined with the water vapor to
set the hydrogen off into space and free the oxygen.
2H2O + UV light energy ----> 2H2 (freed into space) + O2
The newly freed oxygen reacted with methane, forming
carbon dioxide and additional water vapor.
CH4 + 2O2 ----> CO2 + 2H2O
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.
3. What is meant by “free oxygen”?
4. Besides water, what other molecules play a
huge role in photochemical dissociation?
5. What happens when freed oxygen combines
with methane?
6. What happens when freed oxygen combines
with ammonia?
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, eliminating the dangerous radiation and setting
up the foundation for a habitable planet.
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/
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.
Thus, the early Earth was likely a
paradise for methanogens
(methane-producing bacteria) that
fed directly on hydrogen and carbon
dioxide, at least until the
atmospheric hydrogen was depleted.
7. What primitive organism uses photosynthesis to
combine CO2 and water in the presence of sunlight
to make sugar and O2?
8. What are methanogens, and why was early Earth a
paradise for them?
9. Where did these methanogens retreat to, when
oxygen started evolving in our atmosphere?
10. Where did the molecular hydrogen of the Earth’s
first atmosphere likely go?
Many anaerobic microbes including methanogens are
easily poisoned by oxygen, and the recent discovery
of banded sediments with rusted iron suggests that
oxygen-producing, photosynthetic microbes called
cyanobacteria were able to gather sunlight for
photosynthesis. These BIFs would not have formed
without O2 present in the atmosphere.
The evolution of O2 in our
atmosphere spelled doom
for the proliferate
methanogens, and other
types of extremophiles that
had evolved during this early
period in Earth’s past.
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 which evolved
3.5-1.5 billion years ago (also known as
blue-green algae), were remarkably
self-sufficient creatures that could
use the sun’s energy to make their
own food, and fix nitrogen, a process
where nitrogen gas is converted into
ammonia or nitrate. (NH3; NO3)
While this may not seem significant, the cycling of nitrogen on Earth is
essential for life. It is found in amino acids, proteins, and genetic material.
Nitrogen is the most abundant element in the atmosphere (~78%).
However, gaseous nitrogen must be 'fixed' into another form so that it can
be used by living organisms.
10. How do are banded iron formations created…and
why can’t they form anymore?
11. What does it mean to “fix” nitrogen?
12. Why is the cycling of nitrogen so important to life on
Earth?
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 simple, uncomfortable answer is
that we don't really know.
???
We already know that over time, the Earth’s
crust cooled. The crust is thin, relatively,
varying from a few tens of kilometers thick
beneath the continents to less than 10 km
thick beneath 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 plastic largely
through heat generated by radioactive decay.
This heat source is relatively small, but
nevertheless, because of the insulating
properties of the Earth's rocks at the surface,
this is sufficient to keep the asthenosphere
plastic in consistency.
13. Why was there a huge 2 billion year gap between
the first origins of life and oxygen in the atmosphere, and
the appearance of more complex life forms?
14. What is the lithosphere composed of, and what does
it sit on top of?
15. What keeps the asthenosphere plastic?
Energy can be transferred in three ways…
com/watch?v=p0d
of space
 Radiation Energy transfer across the vacuum
WF_3PYh4
 Conduction Energy transfer directly from molecule to molecule (solids)
 Convection Energy transfer through fluids (liquids and gases)
http://www.youtube.
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
16. Give an example of how Earth experiences the
transferal of thermal energy in the form of radiation.
17. Give an example of conduction of thermal energy.
18.Give an example of convection of thermal energy.
19. In what media does each type of thermal energy
transfer?
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.
The heat generated by the lower mantle, drives the convection currents upward
against the lithospheric plates. As the currents cool, they move laterally, pushing
and pulling the lithosphere apart. Then, the currents move downward again, where
they begin to heat up once more due to proximity to lower mantle heat.
While seemingly static, the geosphere is in fact a very active
player in the Earth systems, affecting the atmosphere and the
hydrosphere, as well as critical processes such as the
hydrologic cycle and other biogeochemical cycles.
 The types of minerals contained in soils--a factor of
geologic processes--help to determine the vegetative cover
and ecosystems at the surface.
 Carbon – an essential element of life – is bound in organic
matter and is carried to the ocean via wind and water erosion
where eventually it becomes part of the ocean floor.
20. How does the geosphere influence the biosphere?
21. How does the geosphere influence the hydrosphere?
22. Why has the differentiation of the Earth been so
important a factor in tectonic movement?
Tectonic movement carries the ocean deposits into the
Earth's interior. On geologic timescales, volcanic activity can
vent the carbon to the Earth's atmosphere as carbon dioxide.
The carbon cycle is one of
the key cycles linking the
Earth’s subsystems:
geosphere, atmosphere,
hydrosphere, and biosphere.
The outer core of the Earth contains liquid iron. Its motion is
thought to drive the Earth's magnetic field – the
magnetosphere - which extends far beyond the atmosphere
protecting Earth and its biosphere from solar wind and cosmic
radiation.
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.