– Miller and Urey showed that under conditions postulated to have existed on early Earth, it was possible to spontaneously form essential organic molecules.

e. Why do some scientists believe that RNA, rather than DNA, was the first genetic material? Hint: RNA has been shown to catalyze certain reactions (as part of ribosomes, rRNA participates in the catalysis of the peptide bonds that form proteins). RNA could have evolved into DNA.

Adaptations took advantage of the presence of free oxygen in the oceans and atmosphere by the evolution of cellular respiration, which used oxygen to help harvest energy from organic molecules.

The fossils are considered to be an incomplete record of evolution because the fossil record is biased for the organisms that had hard shells and skeletons.

The fossil record, however, is quite incomplete. Here’s one major reason why: Sediment has to cover an organism’s remains in order for the long fossilization process to begin. So like the mineralized bones themselves, the fossil record is an incomplete framework that scientists flesh out through additional methods.

Fossils are physical evidence of preexisting organisms, either plant or animal. Fossils of any kind are useful in “reading the rock record,” meaning they help us decipher the history of the earth. They can help us determine the geologic age and environment (the paleoenvironment) in which they were deposited.

Fossils are the preserved remains or traces of animals, plants, and other organisms from the past. Fossils are important evidence for evolution because they show that life on earth was once different from life found on earth today.

Fossils also show how animals changed over time and how they are related to one another. Fossils can’t tell us everything. While fossils reveal what ancient living things looked like, they keep us guessing about their color, sounds, and most of their behavior. Fossils are very rare.

The most recent fossils can be found in Cenozoic era. because they can found in the uppermost layer of the rocks.

Cenozoic

There were a few extinctions over this period due to the changing climate but plants adapted to the various climates that emerged after the glaciers retreated.

Lasting 43 million years, the Paleogene is most notable as being the time in which mammals evolved from relatively small, simple forms into a large group of diverse animals in the wake of the Cretaceous–Paleogene extinction event that ended the preceding Cretaceous Period.

In North America, the Cenozoic has traditionally been divided only into the Tertiary Period (66 million to 2.6 million years ago) and the Quaternary Period; however, the notion that the Tertiary should be replaced by the designations Paleogene and Neogene is becoming more widespread.

Divisions. The Cenozoic is divided into three periods: the Paleogene, Neogene, and Quaternary; and seven epochs: the Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, and Holocene.

23.03 million years ago

The Neogene Period was a time of big changes for the earth. The climate became cooler and drier. Grasslands replaced forests. The animals had to adapt to these changing conditions or face extinction.

The Neogene Period started with the replacement of vast areas of forest by grasslands and savannahs. New food sources and niches on the grasslands and savannahs fostered further evolution of mammals and birds. Whales diversified in the seas, and sharks reached their largest size during the Miocene.

The end of the Neogene marked the extinction of most of the flightless, predatory “terror birds” of South America and Australia, the last dregs being wiped out in the ensuing Pleistocene. Otherwise, bird evolution continued apace, with most modern orders well represented by the close of the Neogene. Reptiles.

Neogene