Fossils are the preserved remains of plants or animals. For such remains to be considered fossils, scientists have decided they have to be over 10,000 years old. There are two main types of fossils, body fossils and trace fossils. Body fossils are the preserved remains of a plant or animal’s body. Trace fossils are the remains of the activity of an animal, such as preserved trackways, footprints, fossilized egg shells, and nests.
When asked what a fossil is, most people think of petrified bones or petrified wood. Permineralization is a process. For bone to be permineralized, the body must first be quickly buried. Second, ground water fills up all the empty spaces in body, even the cells get filled with water. Third, the water slowly dissolves the organic material and leaves minerals behind. By the time permineralization is done, what was once bone is now a rock in the shape of a bone. Unlike what you see in cartoons, dogs wouldn’t be interested in these bones.
When an animal or plant dies, it may fall into mud or soft sand and make an impression or mark in the dirt. The body is then covered by another layer of mud or sand. Over time, the body falls apart and is dissolved. The mud or sand can harden into rock preserving the impression of the body, leaving an animal or plant shaped hole in the rock. This hole is called a mold fossil. If the mold becomes filled over time with other minerals the rock is called a cast fossil.
A simple experiment can show you how this works. Take some clay and press a seashell or some other object into the clay. Pull the sea shell out of the clay any you will see a detailed impression of your seashell in the clay. If, over time, the clay hardens into rock the result would be a fossil mold. But really, who has millions of years to wait to make their own fossil? Here’s the quick way. Pour plaster of Paris, dental stone, or other plaster into the mold. Wait for it to harden and you have just made your own cast fossil.
Another type of fossil is a resin fossil. Resin is sometimes called amber. Plants, mostly trees, secrete sticky stuff called resin. Sometimes insects, other small animals, or bits of plants get stuck in the sticky resin. The resin hardens overtime and is preserved in rock making a fossil.
Cacti have many adaptations that allow them to live in dry areas; these adaptations let the plant collect water efficiently, store it for long periods of time, and conserve it (minimizing water loss from evaporation).
Cacti have a thick, hard-walled, succulent stem – when it rains, water is stored in the stem. The stems are photosynthetic, green, and fleshy. The inside of the stem is either spongy or hollow (depending on the cactus). A thick, waxy coating keeps the water inside the cactus from evaporating.
Many cacti have very long, fibrous roots, which absorb moisture from the soil. Some, like ball cacti, have shorter, more compact roots that absorb dew water that falls off the cactus.
Instead of leaves, most cacti have spines or scales (which are modified leaves). These spines and scales do not lose water through evaporation (unlike regular leaves, which lose a lot of water). The spines protect the cactus from predators (animals that would like to eat the cactus to obtain food and/or water). Areoles are circular clusters of spines on a cactus. Flowers bud at an areole and new stems branch from an areole.
Aquatic bird feathers are neatly arranged to repel water, and they use an oil to coat the feathers (similar to wax paper) which makes the water roll right off of them.
Some animals migrate between warm breeding waters and cold feeding waters near Antarctica and in the Arctic. Do you know how whales keep warm when they are in very cold water? They have a thick layer of fat under their skin called blubber. The blubber keeps them warm and also stores nutrients their body can use when they are in waters where there isn’t much food. Other marine mammals like seals and sea lions also have blubber.
Blubber helps keep animals warm because it acts as an insulator. An insulator slows down the transfer of heat, keeping the animal’s body heat from escaping into the water and protecting it from the cold.
The vaseline packs should have allowed you to keep your hands in the icy water much longer than when they are bare. Vaseline acts just like blubber!
Darwin was amazed by the variation in the characteristics of plants and animals he encountered on his journey. In any habitat, food is limited and the types of foods available may vary. Animals that have variations that enable them to take advantage of available foods will be more likely to survive. We call beneficial inherited variations adaptations. Adaptations are inherited characteristics that increase an organism’s chance of survival. Those with the most helpful adaptations will be the most likely to live long enough to pass on their genes to the next generation. This process ensures that beneficial adaptations will continue in future generations, while disadvantageous characteristics will not.