Part One - Geology
Basic Composition of the Earth
The earth is made up of several layers. The atmosphere of the earth is primarily studied by the branch of science known as climatology, or meteorology. The layers of the earth's solid matter are studied by geologists. Many geological features are caused by climatology, due to weathering of the rocks of the earth.
The two main regions of the earth's surface are continents and ocean basins. Continents are large landmasses, composed mostly of granite type rocks, but also composed of sedimentary and metamorphic rocks. Ocean basins are the low-lying portion of the earth's surface which lies between the continental landmasses.
The uppermost surface of the earth is called the crust. There are two main types of crust. Continental crust, which forms the exposed land masses of earth, is approximately 10 to 22 miles thick (16 to 35 kilometers). The other type of crust is known as oceanic crust. This type of crust is only 5 to 10 miles thick (8 to 16 kilometers). The primary difference between these crusts is the mineral composition. The density of oceanic crust causes it to sink in relation to continental crusts. This is an important concept that will be discussed later when we consider tectonic forces.
Continents
There are several major features of continents. Typically, continents have three parts. The first part is known as a shield. A shield is a regional area with low relief (little elevation change). The elevation of a shield is typically within a few hundred yards of sea level. For additional study of shields, click here.
Another part of continents is the stable platform. This feature is characterized by a covering of sedimentary rocks. It is called stable because it has largely remained unchanged for many millions of years. The stable platforms have never been subjected to uplifting tectonic forces.
The third part of
continents is known as folded mountain belts. These
mountains normally occur along the margins, although they can also form on
the continents interior. Typically, except for a few volcanoes,
mountains form in belts, or ranges, because of the collision of two tectonic
plates. The image at right shows a picture of the Himalayan Mountains
as seen from the International Space Station (click image for a larger
view). These mountain ranges can be thousands of miles long, and
hundreds of miles wide. Because of their formation from the collision
of tectonic plates, they are great evidence that the earth's crust is in
motion.
The Tectonic System
The tectonic system
has shaped the continents over earth's history. The word
comes from the Greek word for "builder", which is tecton. The earth's
crust is divided into sections, called plates, or tectonic plates.
These plates actually move
about the surface of the earth. Geologists have taken measurements,
and can tell how far each plate moves in a year. For instance, the
Indo-Australian plate fused together from two plates about 50 to 55
million years ago, and its current velocity is about 67 millimeters per year
(about 2.6 inches). The collision of the Indo-Australian plate and the
Eurasian plate caused the uplift known as the Himalayan Mountains. To
see an animation of this collision between two continental plates,
see
Fig. 19.28- Convergence of Plates-Continent-Continent (298.0K).
The plates move
because of the convection currents in the asthenosphere, or
upper mantle. These
currents are illustrated in the graphic at right. As the currents
move, they pull the plates along, a concept known as slab pull.
When an ocean plate collides with a continental plate, the continental plate
overrides the ocean plate, and the point of collision is known as a
subduction zone. The ocean plate dives underneath the margin
of
the continental plate, and enters the upper mantle (see picture at right).
When two ocean plates or continental plates collide, they normally cause
mountain ranges.
Tectonic movement is also responsible for the formation of many volcanoes, and they are also the source of many earthquakes. You will learn more about tectonics in a later chapter. To learn more now, see Plate Tectonics.
Sedimentary Rocks & Stratum
The study of the earth's history centers upon the study of sedimentary rock layers. These rocks contain the fossils that paleontologists study to examine ancient life forms. These fossils are used in Biostratigraphy to date the relative ages of the rock layers.
The rock material that comprises sedimentary rocks starts out as parts of other rocks, before it is weathered away, and carried by some transportation system, either wind or water, to the point where it is deposited, and then it finally solidifies (lithifies) into a sedimentary rock. The deposition environment includes the physical, chemical, and biological conditions that are present at the location of deposition. Each environment produces rocks which are characteristic of that environment. For example, beaches produce sandstones, but so does wind-blown sand, which produces a desert sandstone.
Finally, compaction and cementation presses the grains together, and "glues" them, making them into rocks. Compaction occurs because the layers of rock on top of each other are compressing the bottom layers, squeezing out moisture, and allowing them to cement together. The cement is commonly calcite, quartz, or limonite.
In geology and related fields, a stratum (plural: strata) is a layer of rock or soil with internally consistent characteristics that distinguishes it from contiguous layers. Each layer is generally one of a number of parallel layers that lie one upon another, laid down by natural forces. They may extend over hundreds of thousands of square kilometers of the Earth's surface. Strata are typically seen as bands of different colored or differently structured material exposed in cliffs, road cuts, quarries, and river banks. Individual bands may vary in thickness from a few millimeters to a kilometer or more. Each band represents a specific mode of deposition—river silt, beach sand, coal swamp, sand dune, lava bed, etc.
Geologists study rock strata and categorize them by the material in the beds. Each distinct layer is usually assigned to a "formation" name usually based on a town, river, mountain, or region where the formation is exposed and available for study. For example, the Burgess Shale is a thick exposure of dark, occasionally fossiliferous, shale exposed high in the Canadian Rockies near Burgess Pass. Slight distinctions in material in a formation may be described as "members" or sometimes "beds." Formations are collected into "groups." Groups may be collected into "supergroups."
Sedimentary rocks
are
deposited in layers, one on top of the other. When you look at a photo
of the Grand Canyon, it is easy to see the layers of rock. Even though
a layer may be completely sandstone, it is important to remember that the
other layers are still being deposited at the same time. For example,
at the shoreline, sand is being deposited which will eventually become
sandstone. Farther out to sea, where a river is pumping mud into the
ocean, mud is accumulating that will later become shale. Still further
out to sea, calcium carbonate may be precipitating, and it will later become
limestone. As the sea level fluctuates, the locations of the
deposition zones for these three materials moves back and forth. This
Youtube
video explains the process
known as transgression and regression.
More on Formations
A formation or geological formation is the fundamental unit of lithostratigraphy. A formation consists of a certain number of rock strata that have a comparable lithology, facies or other similar properties. Formations are not defined on the thickness of the rock strata they consist of and the thickness of different formations can therefore vary widely.
The concept of formally defined layers or strata is central to the geologic discipline of stratigraphy. A formation can be divided into members and are themselves grouped together in groups.
Usefulness of formations
Formations allow geologists to correlate geologic strata across wide distances between outcrops and exposures of rock strata. An outcrop is an exposure of rock deposits at the surface of the Earth.
Geologic formations are usually sedimentary rock layers, but may also be metamorphic rocks and volcanic flows. Igneous intrusive rocks are generally not divided into Formations.
Certain formations throughout the world contain the vast majority of the dinosaur fossils we find. Throughout the curriculum, you will see references to many different rock formations.
Part Two - Biology
Most of the biology that you need to know deals with the classification of animals.
Biological classification, or scientific classification in biology, is a method to group and categorize organisms by biological type, such as genus or species. Biological classification is part of scientific taxonomy.
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Please examine the picture at right. It depicts the normal scientific classification system. An immediately higher rank, superorder, may be added directly above order, while suborder would be a lower rank. For example, looking at the classification for Stegosaurus, it belongs to the Superorder Dinosauria.
Most of the dinosaurs in this curriculum are studied at the genus level. For example, there is one Lesson for Stegosaurus. However, there are three species of Stegosaurus, and one further species that is considered dubious. In zoological nomenclature, a nomen dubium (Latin for "doubtful name", plural nomina dubia) is a scientific name that is of unknown or doubtful application. A species may be dubious if there is not enough scientific data to support the individual species.
In order to help you out, many of the hyperlinks for terms you may not be familiar with have been left in the text. Click the links if you need more information. To get you started, here are a few definitions, in no specific order, that you will need to know:
A clade is a group consisting of a species (extinct or extant) and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life"
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior. Some dinosaurs exhibit differences in male vs. female skeletons.
Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs, or legs. For example, raptors, and T-rex, are bipedal.
Quadrupedalism is a form of land animal locomotion using four limbs or legs. An animal or machine that usually moves in a quadrupedal manner is known as a quadruped, meaning "four feet"
In biology, a type is one particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralize the defining features of that particular taxon. The term you will see frequently in this curriculum is "type species, or type specimin."
Ecological Niche - In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food resources and foraging methods. A shorthand definition of niche is how an organism makes a living. The ecological niche describes how an organism or population responds to the distribution of resources and competitors (e.g., by growing when resources are abundant, and when predators, parasites and pathogens are scarce) and how it in turn alters those same factors (e.g., limiting access to resources by other organisms, acting as a food source for predators and a consumer of prey).
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