How old is bedrock

Rocks of Mesozoic age in Minnesota tell the story of two major marine trangressions or sea level rises : one during the Jurassic Period roughly million years ago and one during the Cretaceous Period roughly million years ago. The poorly understood Jurassic rocks are known only from drill core samples in the far northwestern corner of the state Fig. They include shale, limestone, dolostone, sandstone and siltstone possibly deposited within streams, lakes, and other marginal-marine environments as a sea over much of North Dakota and other western states slowly advanced eastward.

The Cretaceous rocks form a nearly continuous blanket covering the Paleozoic and Precambrian rocks throughout the western half of Minnesota and numerous, small outliers in the eastern half of the state Fig. These rocks consist primarily of weathered residuum and overlying sedimentary rocks of conglomerate, sandstone, mudstone, shale, marl, and minor limestone.

The residuum, which spans both the western and eastern half of the state, developed during a long period of weathering and erosion from sometime after the Middle Devonian roughly million years ago to the Late Cretaceous roughly million years ago , after which the overlying sedimentary rocks were deposited.

The Cretaceous sedimentary rocks formed within a transitional marine and nonmarine environment along the eastern shoreline of a large inland sea, known as the Western Interior Seaway, that once split North America into two landmasses. Fossilized shark teeth, snails, clams, ammonites, fish bones and even crocodile parts are known from the marine and marginal-marine deposits in southwestern and northeastern Minnesota, while fossilized leaf impressions and pollen have been identified in some of the nonmarine deposits in the southeast Fig.

Click here to open the web map in a new window. It portrays our current geologic understanding of the temporal and geographic distribution of units within major Precambrian terranes and of the Phanerozoic strata Paleozoic and Mesozoic bedrock. The western part of the mapped Precambrian terrane is inferred largely from geophysical maps, anchored locally by drilling.

In many places, contacts are drawn between units of the same or similar apparent rock type and same unit label ; these are recognized as geometrically distinct, though geophysically or lithologically similar. Click here to download the publication version. Breadcrumb Home Bedrock Geology. Bedrock Geology. Learn more about geologic time.

Above the bedrock lies remnants of the million-year-old Caledonian mountain range, which is a distinct belt along the Western Scandinavia. The youngest rocks to be found in Norway, on land, are in the Oslo Rift and provide evidence of volcanic activity million years ago. This knowledge is the basis for understanding how the rocks and landscapes have changed through time and in line with the changes in tectonic conditions continental drift , the climate and the evolution of the Earth's life forms.

In the bedrock lies vital natural resources, in the form of stone building materials, ores and minerals, which are all necessary for the functioning of modern society. The key to understanding how we can best find these valuable resources is to improve our knowledge of the origin and composition of various rock types. The bedrock map of Norway, along geophysical maps, shows the geographic position and depths of rocks of varying age and origin.

Map created by U. Geological Survey. The map above shows the ages of bedrock in North America from yellow youngest to green to blue to red oldest.

It was created by Kate E. Empower your students to learn about the rock cycle with this collection of resources.

Erosion is the process where rocks are broken down by natural forces such as wind or water. There are two main types of erosion: chemical and physical. In physical erosion, the rock breaks down but its chemical composition remains the same, such as during a landslide or bioerosion, when plants take root and crack rocks. Explore the process of erosion with this collection of resources. An abiotic factor is a non-living part of an ecosystem that shapes its environment. In a terrestrial ecosystem, examples might include temperature, light, and water.

In a marine ecosystem, abiotic factors would include salinity and ocean currents. Abiotic and biotic factors work together to create a unique ecosystem.

Learn more about abiotic factors with this curated resource collection. Weathering is the process of the weakening and breakdown of rocks, metals, and manmade objects. There are two main types of weathering: chemical and physical. An example of chemical weathering is acid rain. Caused mostly by the burning of fossil fuels, acid rain is a form of precipitation with high levels of sulfuric acid, which can cause erosion in the materials in which it comes in contact. An example of physical weathering is wind blowing across the desert playas.

This process causes rocks to form a specific pyramid-like shape and they are called ventifacts. Select from these resources to teach about the process of weathering in your classroom. Sedimentary rocks are one of three main types of rocks, along with igneous and metamorphic. Metamorphic rocks start as one type of rock and—with pressure, heat, and time—gradually change into a new type of rock.

Weathering describes the breaking down or dissolving of rocks and minerals on the surface of the Earth. Water, ice, acids, salts, plants, animals, and changes in temperature are all agents of weathering.

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Encyclopedic Entry Vocabulary. Bedrock is the hard, solid rock beneath surface materials such as soil and gravel. Bedrock also underlies sand and other sediment s on the ocean floor. Bedrock is consolidated rock, meaning it is solid and tightly bound.