The Pale Blue Dot
There are two things the earth has in rather sharp contrast with the other planets:
Undoubtedly the Earth was heavily impacted at the same time the moon was but its surface has been completely reworked since then so there is no evidence for this event.
On average, the current surface of the earth is 500 million years old
The Earth's Surface is kept young by Plate Tectonics:
In the oceans, species don't have to deal with whole changes in the physical characteristics of their ecosystem.
As we will discuss later, the earth currently has significant climate variations on a timescale of 100,000 years. In addition, over the last 200-250 million years the earth is experiencing an era go global tectonic motion which makes the land surface a Dangerous Place to Live:
Summary of Evidence for Plate Tectonics:
Summary of Evidence for Plate Tectonics:
The earth's crust is actually a two-component layer. The lithosphere is a thin layer of rock (average density of 2.7 grams per cc) and "floats" on top of a plastic-like layer called the asthenosphere. Plastic-like materials are weird - they deform under stress but don't really break. A glacier is a good example of a material that moves and flows plastically. The convective heat currents in the mantle impinge on the asthenosphere causing deformation and subsequent movement of the lithospheric plates.
This process can be simulated in your kitchen by putting some jello in a bowl and putting some peebles on top of the jello. As you shake the bottom of the bowl, the jello deforms but doesn't break and the rocks that float on the jello collide. (apologies to real geologists for this analogy).
As a result of plate movements, interesting things occur at plate boundaries. In general you don't want to live near a plate boundary as the earth is active there. About 75% of the world's population does live near these boundaries.
There are three types of plate boundaries:
Local Manifestations of Plate Tectonics:
Some Other Internet Resources on Plate Tectonics:
Another overview of all of this
Imaging the Ocean Floor
And now for something completely different.
Imaging the Earth to detect Intelligence:
Although we may think we are a creative species, we do not manifest that creativity on large scales. Indeed, the largest man-made object which can be seen from space is a linear device known as the Great Wall of China.
As we will discuss later, "intelligent" life on the earth principally manifests itself via escaping electromagnetic radiation principally in the form of Television Broadcasting and Military Radar. An exquisite combination to symbolize the collective intelligence of the planet.
Let's imagine that we live on a distant planet that has intercepted some of this stray radiation (and that we don't work for the NSA ). We decide to send an imaging spacecraft to the Earth to learn more about the source that has produced the signal.
Hypothetical Journey to earth to find intelligent life:
As we get closer to the earth and our picture resolution improves we begin to notice deviations from the natural landscape but not at this resolution scale which is already pretty high. These deviations are clustered on the land surface and have a morphology that is independent of the continental land mass upon which they are located. They appear as grid patterns .
The grid patterns do not respect continental boundaries, they are everywhere the same. This is a large scale manifestation of the erasure of culturual differences through Technology. As we zoom in on the grid we see collections of rectangular plots laid out. Further zooming delineates some boundaries.
Further zooming begins to reveal individual structures which are immobile and embedded in the overall grid pattern. This pattern is consistent from one grid pattern to another. Whatever has built these structures has done so in a uniform manner. But still no motion has been detected. Improved resolution begins to show the transport mechansisms and any observed motion is highly ordered. At the very high resolution image scale we finally observe the objects that move
Now we are done. We have a consistent picture of the nature of intelligence on the earth. It is uniform and rigid, always repeating the same pattern. Small, metallic mobile units function within the larger foundation if well-defined grid. But have we missed anything.
We descend closer and reach a resolution limit of 1-meter. We notice a large rectangular object (okay a bus) become immobile and a bunch of stuff pours out and moves in random and chaotic patterns. We conclude that the intelligent life on the earth must really do something about these parasites!