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~SgtMajH's Geologic Time EarthCache~

A cache by SgtMajH Send Message to Owner Message this owner
Hidden : 10/23/2015
2 out of 5
2 out of 5

Size: Size: other (other)

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Geocache Description:

Geologic Time Scale

Lake Washington Brevard County, Florida

Answers MUST be sent PRIOR to logging your find or your log will be deleted!

It is the 41st largest lake in the state of Florida. It is approximately 4 by 1 mile (6.4 by 1.6 km) and 10 to 15 feet (3.0 to 4.6 m) deep. Located adjacent to the City of Melbourne, it is the single most important source of fresh water for the city and the surrounding areas. It furnishes two-thirds of the water to Melbourne's 150,000 customers.

Lake Types

Periglacial lake: Part of the lake's margin is formed by an ice sheet, ice cap or glacier, the ice having obstructed the natural drainage of the land.

Subglacial lake: A lake which is permanently covered by ice. They can occur under glaciers, ice caps or ice sheets. There are many such lakes, but Lake Vostok in Antarctica is by far the largest. They are kept liquid because the overlying ice acts as a thermal insulator retaining energy introduced to its underside by friction, by water percolating through crevasses, by the pressure from the mass of the ice sheet above or by geothermal heating below.

Glacial lake: a lake with origins in a melted glacier, such as a kettle lake.

Artificial lake: A lake created by flooding land behind a dam, called an impoundment or reservoir, by deliberate human excavation, or by the flooding of an excavation incident to a mineral-extraction operation such as an open pit mine or quarry. Some of the world's largest lakes are reservoirs like Hirakud Dam in India.

Endorheic lake, terminal or closed: A lake which has no significant outflow, either through rivers or underground diffusion. Any water within an endorheic basin leaves the system only through evaporation or seepage. These lakes, such as Lake Eyre in central Australia or the Aral Sea in central Asia, The Great Salt Lake in Western United States, are most common in deserts.

Meromictic lake: A lake which has layers of water which do not intermix. The deepest layer of water in such a lake does not contain any dissolved oxygen. The layers of sediment at the bottom of a meromictic lake remain relatively undisturbed because there are no living aerobic organisms.

Fjord lake: A lake in a glacially eroded valley that has been eroded below sea level.

Oxbow lake: A lake which is formed when a wide meander from a stream or a river is cut off to form a lake. They are called "oxbow" lakes due to the distinctive curved shape that results from this process.

Rift lake or sag pond: A lake which forms as a result of subsidence along a geological fault in the Earth's tectonic plates. Examples include the Rift Valley lakes of eastern Africa and Lake Baikal in Siberia.

Underground lake: A lake which is formed under the surface of the Earth's crust. Such a lake may be associated with caves, aquifers or springs.

Crater lake: A lake which forms in a volcanic caldera or crater after the volcano has been inactive for some time. Water in this type of lake may be fresh or highly acidic, and may contain various dissolved minerals. Some also have geothermal activity, especially if the volcano is merely dormant rather than extinct.

Lava lake: A pool of molten lava contained in a volcanic crater or other depression. Lava lakes that have partly or completely solidified are also referred to as lava lakes.

Former: A lake which is no longer in existence. Such lakes include prehistoric lakes and lakes which have permanently dried up through evaporation or human intervention. Owens Lake in California, USA, is an example of a former lake. Former lakes are a common feature of the Basin and Range area of southwestern North America. Ephemeral lake, intermittent lake, or seasonal lake: A seasonal lake that exists as a body of water during only part of the year.

Shrunken: Closely related to former lakes, a shrunken lake is one which has drastically decreased in size over geological time. Lake Agassiz, which once covered much of central North America, is a good example of a shrunken lake. Two notable remnants of this lake are Lake Winnipeg and Lake Winnipegos.

Eolic lake: A lake which forms in a depression created by the activity of the winds. Vlei, in South Africa, shallow lakes which vary considerably with seasons.

Epishelf lakes, unique lakes which exist on top of a dense saltwater body and are surrounded by ice. These are mostly found in the Antarctica.

Geologic Time

During the 150 years before radiometric dating was used to determine the absolute ages of rocks, geologists began to group rock layers into time groups and assigned each group a name, creating a relative geologic time scale. Each name in the time scale marks a highlight in the historical development of geological science over the past 200+ years. Nearly every name is associated with a significant event or an important place where a rock was identified or important scientific discovery was made. Over the last 100 years, the study of fossils has defined the time scale even further. For example, the Cambrian Period is so named for Cambria, the Latin name for Wales, where these rocks were first studied. The Carboniferous Period is so named because during this time period a large amount of coal-bearing rocks formed, with coal being composed mostly of carbon. The period is further broken down into the Pennsylvanian (named after the state of Pennsylvania) and the Mississippian (named after the upper Mississippi Valley) epochs that contain these coal-bearing formations.

The time scale is divided into the following categories from largest to smallest time

Eon – Era – Period – Epoch – Age

For example:

Phaneozoic – Mesozoic – Jurassic – Middle – Bathonian (Eon) (Era) (Period) (Epoch) (age)

An understanding of the meaning of the eon/era names and events that marked each one is necessary in order for a basic understanding of geologic time.

Precambrian – This eon represents the bulk of the time scale, spanning from about 570 million years ago to the evolution of the Earth at 4.54 billion years ago. Rocks from this time are mainly complex metamorphic and igneous rocks that form a large volume of the continental crust. There are very few fossils from this time period, due to the fact that life was primitive and had not evolved hard body parts. However, in some special circumstances, such as in the Ediacara Hills in South Australia, these primitive soft-bodied life forms can be found well preserved.

Paleozoic – means “ancient life” and the era marks the time (570 million years ago) at which fossils become abundant. In fact, the start of the Paleozoic is referred to as the “Cambrian Explosion” due to the seemingly sudden development of a vast array of life forms that are preserved as fossils. The variety of life that evolved is astounding, including marine organisms, fish, amphibians, land plants, and even huge insects. The Paleozoic era ended about 250 million years with the opposite event, the “Permian Extinction,” during which more than 80% of all of Earth’s life forms disappeared.

Mesozoic – means “middle life”. Fossil reptiles and invertebrates dominate these rocks. Many of the Earth’s major mountain ranges also were formed. The era’s most famous denizen is the dinosaur, and reptiles (as well as flora) thrived in the generally mild climates that dominated most continents. Pangaea, a huge supercontinent that formed during the late Paleozoic, began to break up during the Mesozoic. The era again ended with another mass extinction, whose cause is often attributed to a collision of a comet or meteor. This extinction however caused the destruction of the dinosaurs.

Cenozoic – means “recent life” and is currently still in progress. Most fossils are related to modern forms, including mammals, modern plants, and invertebrates. Mammals are the dominant vertebrate life form. The first fossils of humans and humanlike animals appear about 3 million years ago, with Homo sapiens (modern humans) evolving about 50,000 years ago.

A Relative Time Scale with Absolute Time

The frosting on the geologist’s cake came when the use of radiometric dating, which became widespread in last 50 years, completely confirmed the relative age correlations made by geologist over the past 150 years. Strata in Canada, that were believed to be much older than certain strata in Europe, were found to be exactly that – much older! Rocks that appeared to be only slightly younger than others were only slightly younger! As more and more rocks were analyzed, the geologic time scale became more and more absolute.

Modern geologic time scales contain both absolute ages and the relative age names. Some also contain other information, such as the Earth’s magnetic polarity over time (which will be covered in another unit).

Logging Requirements

1) What type of lake do you believe this is?

2) Using your GPS, what elevation is the GZ?

3) During what time period do you believe this lake formed and why?

4) While not required, please show your view from this location of the lake. (Optional)

5) What age is known as the "Cambrian explosion"?

The purpose of this Earthcache is to both learn a little bit about the geography of this area and hopefully gain some knowledge that you might not have known. More important than logging this cache is the hopes of gaining a little knowledge of this area!

There is no right or wrong answer! So, don't worry about your answers. The one exception is question #5 Which does have a correct answer but don't worry, you will still be able to log the cache and I will provide you with the correct answer! Thank you for visiting my Earthcache.

Please do not post your answers in the log and do not post a smiley without emailing your answers as your log will be deleted.

FTF Congratulations to my dear friends TeamE88!!!! I am thrilled that you were able to FTF this!

Additional Hints (No hints available.)

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