- 2106 -
Earth is finely tuned for life.
How did it get that way? Are we
here as a result of random collusions and mutations? We only know life that is us. That is a sample size of one. Regardless, Earth's history demonstrates that life can
take root and evolve. Here is what we
haven learned.
-
-
------------------ 2106
- How Did I Get Here??
-
- It is an amazing story. You may find it hard to believe. It all started 13,800,000,000 years ago when
the Universe started expanding. Energy
and matter are two forms of the same thing.
But we needed matter to form stars.
Stars happened about 13,000,000,000 years ago with only about 0.03% of all
the mass/energy in the Universe
-
- Originally
the stars were made up of only hydrogen and helium. Giant stars were crushed by gravity. When atoms themselves got crushed into a
rebound that resulted in a giant explosions, called a supernovae.
-
- It took
billions of years of repeated star formations and star explosions to create
enough heavy elements out of the merging of protons and neutrons and electrons
into the elements. We find all these elements in the Periodic Table of Elements
today. Those elements are what was
needed to form our Sun and planets in our solar system.
-
- Our Sun
happens to be in a perfect zone in our Milky Way Galaxy. It was in the right position to allow the
formation of rocky planets that could orbit
around it. The Earth got lucky because
it orbits the Sun at just the right position to host liquid water at the right
temperature.
-
- The Earth
also lucked out having a metallic core and a powerful magnetic field. That magnetic field protected the surface
from being bombarded by harmful radiation.
The plate tectonics at the surface were active enough to replenish the
Earth's surface with nutrients and to stabilize the temperatures. Our Moon was likely responsible for keeping
Earth's tilt at 23.5 degrees. This allowed the seasons and the changes needed
for the diversity of life on Earth.
-
- 3,400,000,000
years ago these conditions allowed a single celled organism called a
prokaryotes to form. But, it took
another 2 billion years before there was a merging of these cells and another
billion years before multi cellular life formed. These multi cellular life forms proliferated
550,000,000 years ago. It is what is called the Cambrian Era Explosion.
-
- Somehow we
got from multi cellular life to the development of an intelligent species. We somehow advance enough for me to write
this Review. Somehow we humans advanced
far beyond our close animal relatives. Somehow our species escaped extinction
several times in the process.
-
- Astronomers
have found thousands of planets orbiting other stars and they have found billions
of more stars in billions of more galaxies.
Given the sheer numbers could the Earth really be unique among so many
planets?
-
- But the Earth
must be unique with very rare conditions that would allow the evolution of
life. From that aspect we might very
well be irreproducible? We come from a
long chain of implausible coincidences.
-
- We have good
reason to conclude that we are only technological civilization in our own
galaxy.
-
- Our Sun
contains 71 % hydrogen, 27% helium, and only 2% of the rest of the elements in the
Periodic Table of all elements. The
Earth and the other planets formed out of that small 2% of construction
material.
-
- Then there
are these extinction events: We have seen Gamma-Ray Bursts in other galaxies. From these observations astronomers predict
that our Milky Way galaxy would experience such an event every 1 to 100 million
years. A single burst would sterilize
most of the galaxy.
-
- The habitable
zone in our galaxy extends only 23,000 to 30,000 light years from the galactic
center. We just happen to be 24,500
lightyears from that center. At the same
time we just happen to be within the habitable zone of our own solar
system. Liquid water is the basic sign
for habitat and Venus and Mars orbiting on either side of us are missing liquid
water.
-
- Plate
tectonics on Earth's surface brought nutrients to the surface to replenish that
depleted by living cells. These
tectonics were necessary to recycle carbon and to stabilize temperatures over
long time scales. Earth's magnetic core
and rapid rotation shielded the surface from harmful radiation. Without the shield the atmosphere would have
eroded and the surface would have fried.
-
- Scientist
believe the Moon was responsible. The
giant collision that splashed the Moon into orbit also created Earth's metallic
core and its floating crust. The
relatively large moon orbiting Earth was a type of stabilizer allowing Earth's
axis not to wobble in its orbit. T he Earth - Moon partnership is a rare
happening. Without it we would likely
not be here.
-
- Once all this
planetary juggling settled down somehow life started. Single cell organisms in rocks have been dated
to be 3.4 billion years old. The Sun and
Solar System formed 4.5 billion years ago.
That is when life started, but, it remained at the microbe level for the
next 3 billion years. In fact, those same microbes are alive with us today.
-
- These simple
cells are called prokaryotes. They are
merely a bag of jelly containing the molecules of life, we call DNA. The more complex cells are called
eukaryotes. They first came on the scene
1.5 billion years ago.
-
- Somehow after
3 billion years these primordial single cells merged into organisms called
bacteria and archaea. Somehow these guys
started eating each other and using their raw materials to grow and
multiply. Life started from these simple
cells. At this cellular level there is
no difference between your cells and those of a mushroom, or any other life on Earth.
-
- The
eukaryotes forming multi cellular organisms did not happen until 550 million
years ago. This outburst of life forms is known as the Cambrian Era. How it got to humanity is written in our
genes. One conclusion from analysis of
these genes is that chimpanzees living in central Africa differ from one
another genetically no more than humans do living from opposite ends of the
world. This means that both started out
from their same gene pool.
-
- Some 150,000
years ago the human gene pool was reduced to a few thousand, a few hundred
breeding pairs. Some 70,000 years ago our
population on Earth was again reduced to about 1,000. The 7 billion people on Earth today are
descendents of this small group. How
likely is our advancement to the technological society we have today likely to
get repeated.
-
- Could this
really happened somewhere else in our galaxy?
How likely is 4 billion years of a chain of events likely to repeat itself? It all suggests that we are unique on our
planet and even in our own Milky Way Galaxy.
All the more reason to take care of what we have. It will be hard to repeat it.
-
- Are life's
beginning on Earth so convoluted and unlikely that we are alone in the entire
Universe? Yet somehow life began on
Earth as soon as it was possible to begin.
The molten Earth had barely cooled enough. Immediately when asteroids and comets stopped
pummeling Earth 4 billion years ago life got started.
-
- We are here
for a purpose. One purpose is to try and
understand all of this. Our knowledge is
but a few seashore pebbles on the sand with a whole ocean of unknown before us.
Im; working on it. Hope you learned something?
-
- September 24, 2018
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--------------------- Monday, September 24,
2018 -------------------------
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