Fossils

Big Ideas Fossils give evidence of evolution. Fossils of original preservation Fossils with altered hard parts Index fossils Molds and casts Trace fossils

Evolution The change in populations as a result of an altered environment.

About 12 million years ago, a volcano in southwest Idaho spread a blanket of ash over a very large area. One or two feet of this powdered glass covered the flat savannah-like grasslands of northeastern Nebraska.Most of the animals which lived here survived the actual ashfall, but as they continued to graze on the ash covered grasses, their lungs began to fill up with the abrasive powder. Soon their lungs became severely damaged and they began to die. The smaller animals died first (smaller lung capacities) and finally, after perhaps three to five weeks, the last of the rhinos perished. Their bodies were quickly covered by the blowing and drifting ash.Undisturbed except by an occasional scavenging meat-eater, the skeletons of these animals are preserved in their death positions, complete with evidence of their last meals in their mouths and stomachs and their last steps preserved in the sandstone below.

Original preservation Tar Freezing Amber (tree sap) Oxygen deprivation

When this photograph was taken around 1910, the location depicted was described as "the Salt Creek oilfields, 7 miles west of Los Angeles." Today, this spot is in the middle of downtown Los Angeles.

1907 U.S. Geological Survey drawing shows how oil from underground rock layers migrates upward to fill the La Brea pits.

Don’t cry for me, for I shall live on as a fossil in 2007!

Spider preserved in Amber, or tree sap.

Bog bodies are often inadvertently damaged, as a result of peat mining efforts.

Left: English locations for bog body discoveries. Right: A reconstruction of a bog body discovery. Below: A bog body as it was found.

Another name for permineralization is petrification Another name for permineralization is petrification. The hard parts have been removed and replaced by rock minerals.

Index fossils tell how old the surrounding rocks are, if one knows how old the fossil is. Good index fossils Are very widespread. Existed during a short period of time on Earth. Are of a life form that was very abundant.

A mold is when the organism has died, and left only an impression of itself for us to remember it by.

A CAST is when the MOLD fills in with sediment. This flattened fossil cast of the Sigillaria tree was found in the roof of an underground coal mine-- lodged in the base of a small sandstone channel that marks the boundary of a meandering stream that flowed 300+ million years ago along an ancient delta that existed then.

Trace fossils are just evidence of past life, like casts or molds of footprints or burrows.

Absolute age Relative age, compared to others Absolute age, age in years (bce) Tree rings Varves Half-life

Match up the “bar codes”, and work your way back.

Varves are very similar to tree rings, with the dark being winter floods, and the light being the summer floodings.

KEY POINTS Each living things has the same percentage of C-14 as each other living thing. After death, the C-14 turns into N-14 at a pretty constant rate. About 50% of the existing C-14 turns into N-14, each 5,730 years. All radioactive elements have half lives.

He was found With expensive furs and shoes With bronze points for his arrows With a full belly of food With food in a pack on his back With a probable, fatal arrow wound in his back. The arrow was probably shot from about 20 to 30 feet away He probably died high in the montains Who killed him, and why.