Welcome to Soldiers Delight Natural Environmental Area. This earthcache will teach you about the type of rocks that predominate here, where they come from, and how that has basically defined the area here. Since this is an earthcache, there is no physical container to find or log to sign. Please read through the description below and answer the logging questions.
Soldiers Delight is a sensitive area. Park staff ask that you PLEASE remain on established trails. The area contains endangered plants and easily-damaged rock, for reasons that you'll discover in the lesson below. (There are also plenty of ticks, for reasons that are not necessarily related to the local geology.)
Due to the nature of the soils in the area (see below), the trails around here will be muddy if is raining or has rained recently, so plan accordingly.
LIKE ONIONS (AND OGRES), EARTH HAS LAYERS
As most folks learn in grade school (but here's a quick primer/refresher just in case), the Earth is made up of layers. While there are actually a few more, for today's purposes, generally think of three layers.
On the surface is the lithosphere, the top layer of which is the crust, the only part of the planet most of us will ever see.
In the center is the core, which fluctuates from about 4,400° Celsius (7,952° Fahrenheit) to about 6,000° C (10,800° F), about the temperature of the surface of the sun.
Between the core and the lithosphere lies the mantle, which is 1800 miles (2900 km) thick. It makes up nearly 90% of the Earth's volume and makes up about 2/3rds of Earth's mass.
The Earth's lithosphere is relatively thick, ranging from 25 miles (40 km) to 170 miles (280 km), so normally we don't see rocks from the mantle that have pushed up to the surface. Geologists have theorized that the mantle rocks at Soldiers Delight and a few other scattered locations near Baltimore were thrust to the surface by continents colliding with each other.
HOW ARE ROCKS FROM THE MANTLE DIFFERENT?
Rocks from the mantle have a very different chemical makeup than typical surface rocks. Rocks from the surface typically contain more quartz, calcium, and aluminum. Rocks from the mantle have higher concentrations of magnesium and chromium. (You can learn more about the chromium mines at GCQV5X nearby.) As these mantle rocks weather away, they form thin, sand- and clay-poor soils that easily erode.
This means that the soil here contains much higher concentrations of magnesium than normal. Typical soils contain equal parts magnesium and calcium, but here, the ratio is closer to 4 parts magnesium to 1 part calcium. This is toxic to many plants. Only plants that have adapted to these conditions can grow here - basically scrub oaks and pines, junipers, and grasses.
European settlers in the area learned over time that their crops did not thrive in the soils here. Because grasses did, the area was more used for range land, grazing cattle and other livestock, and not for farming.
PLANETARY GEOLOGY - THE MARS CONNECTION
Unlike on Earth, where rocks from the mantle are relatively rare on the surface, the surface of Mars is covered with mafic lavas - formerly molten rock from its mantle. So, the rare spots where mantle rocks are visible here on Earth are thought to be relatively comparable to conditions on Mars.
LOGGING THIS EARTHCACHE
To log this earthcache, please send us a message (preferred) or email us, copying and pasting the questions and then including your answers. Group finds are fine, please just let us know who was in the group so we aren't bugging anyone for the answers when they've already been sent for the group.
Please do not post these answers in your found it log.
1. The name of this earthcache: GC9BC35 Planetary Geology on Earth: Hiking the Mantle (if you send us a message, this is already done for you).
2. Observe: Look into the open mining pits. Describe the exposed rock you see along the walls - colors, textures, layers, etc.
3. Observe: Describe the rock you see exposed along the trail - colors, textures, layers, etc. Is it solid or cracked? Is it easy or difficult to chip?
4. Observe and think: Read through the description on soils here at Soldiers Delight, and look around the area. If rocks from its mantle are more common on Mars than on Earth, how do you think this would affect attempts to grow food in Martian soil?
5. Please take a photo of yourself, or a personal item such as your team name or a coin, with the mine pits visible in the background, and add it to your "found it" log. If you prefer privacy, you can include the photo to your message with your answers.
SOURCES
National Geographic, "Rare chunks of Earth’s mantle found exposed in Maryland."
George L. Guice et al., "Suprasubduction zone ophiolite fragments in the central Appalachian orogen: Evidence for mantle and Moho in the Baltimore Mafic Complex (Maryland, USA)."
Maryland Geological Society, "Soldiers Delight, Baltimore County."
Maryland Department of Natural Resources, "Soldiers Delight."
J.G. Blank et al., "An alkaline spring system within the Del Puerto Ophiolite (California, USA): A Mars analog site."
Lunar and Planetary Institute, Universities Space Research Association, "The Mantle of Mars: Insights from Theory, Geophysics, High-Pressure Studies, and Meteorites."
Wikipedia: Mantle, Layers of the earth
This earthcache was placed with the permission of the Maryland Department of Natural Resources - thank you!