Fossils, or preserved parts of organisms from the distant past, have shown that species change over time. Radiometric dating can be used to determine the age of fossils by measuring the how much of the radioactive materials in each rock layer have broken down.
Answer:
I think you're referring to the Metaphase...
Explanation:
During Cell Division (or, rather before!) the DNA needs to be replicated. This normally is done by DNA Polymerase, and results in two identical double strands (the "Sister Chromatids".
These chromatids are held together at the Centromere, which will be the heart of the "X"-shape. After that the DNA is packed into Chromosomes by winding it around proteins called Histones. If I remember correctly there are 5 different Histones.
This "Zipping Up" makes the chromosomes more visible.
As the two sister chromatids are still connected, the result is the X-shaped Metaphase Chromosome....
Answer: There are many sources of light, but the initial energy for all light sources comes from the sun. Light travels away from its source in straight lines through space as waves of energy. The waves we can detect with our eyes are called visible light. Patterns in the behavior of light are predictable because light moves in waves through space until it comes in contact with an object or material that changes its direction. Light can pass through or bounce off objects. Additionally, different materials can block or absorb light. If an object blocks light, a shadow of the object forms. If the intensity or direction of the light source changes, the appearance of an object’s shadow can change in size, shape, or darkness. Absorbing light energy can cause changes in matter. A common example includes the color of paper or fabric fading as the matter absorbs light over time. Vibrations cause sounds. We can hear when sound waves travel through the air to our ears and cause our eardrums to vibrate. Sound can also travel through other forms of matter, such as liquids and solids.
Explanation:
