A mineral is a naturally occurring, inorganic solid with a crystalline structure and a definite chemical composition. Minerals form naturally in the Earth, such as quartz from cooling magma or halite (table salt) from evaporated seas. Being a solid means they have a definite shape and volume. Inorganic means they generally lack carbon and hydrogen bonds. Minerals also have a repeating crystal pattern formed by a basic building block called a unit cell, which determines the mineral’s structure. All minerals can be classified based on their crystal structure.
Rocks are made of one or more minerals (and sometimes organic material), but they do not have the consistent chemical composition or repeating atomic structure that minerals do. There are three main types of rocks:
Igneous rocks form from molten rock (magma inside Earth or lava on the surface).
Metamorphic rocks form when existing rocks change due to heat and pressure. They can be foliated (layered) or non-foliated (not layered).
Sedimentary rocks form from sediments, which are pieces of pre-existing rocks or remains of living organisms that accumulate and harden over time.
In short, minerals are the building blocks of rocks, but rocks are mixtures of minerals and sometimes organic materials.
This video from MooMoo Math and Science explains the rules for working with positive and negative numbers in multiplication, division, addition, and subtraction.
For multiplication and division, the same rules apply:
If the signs are the same, the answer is positive.
If the signs are different, the answer is negative.
For addition:
If the signs are the same, add the numbers and keep the sign.
If the signs are different, subtract the numbers and keep the sign of the number with the larger absolute value.
For subtraction:
Subtract and keep the sign of the larger number.
If subtracting a negative number, change it to addition (subtracting a negative becomes adding a positive).
Alfred Wegener noticed that the continents look like they fit together like puzzle pieces and believed they were once joined as one large landmass. This idea became known as the theory of continental drift, which states that continents slowly move over time.
To support his theory, Wegener gathered several types of evidence. First, the shapes of continents, especially South America and Africa, match closely. Second, glacial evidence shows similar glacial scratch marks in Africa, South America, India, and Australia, suggesting these areas were once connected.
Wegener also used fossil evidence. Fossils of the freshwater reptile Mesosaurus were found in both South America and Africa, making it unlikely the animal crossed an ocean. Other fossils, including Cynognathus, Lystrosaurus, and the plant Glossopteris, were found on continents now far apart, supporting the idea they were once joined.
In addition, Wegener matched mountain ranges across continents, such as the Appalachian Mountains and similar ranges in Europe and Greenland. He also found coal deposits in Antarctica, indicating it was once warmer and closer to the equator.
Although Wegener died before his theory was accepted, later discoveries confirmed that continents move due to plate tectonics, and his ideas became an important part of modern Earth science.
Life science is the study of living things, from large ecosystems down to tiny cells. It begins with biomes, which are large regions with similar climates, plants, and animals, including terrestrial and aquatic biomes. Organisms in each biome have adaptations that help them survive, and energy connects all living things through food chains, food webs, and energy pyramids, starting with producers and moving to consumers.
Life is built from cells, the smallest units of life. Cells contain organelles such as the nucleus, mitochondria, cell membrane, and vacuole, which work together to keep the cell functioning. Cells grow and reproduce through the cell cycle, including interphase and the stages of mitosis. Inside the nucleus is DNA, which carries instructions for life and allows traits to be passed from parents to offspring, a process called heredity, studied in genetics.
Living things are organized in levels—from cells to tissues, organs, organ systems, and organisms. Scientists classify life into six kingdoms. The human body shows this organization through systems that work together to keep us alive. Finally, life on Earth changes over time through evolution by natural selection, explaining the diversity of life as populations adapt across generations.
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