AP BIOLOGY

Detailed explanation-1: -The earliest life forms we know of were microscopic organisms (microbes) that left signals of their presence in rocks about 3.7 billion years old. The signals consisted of a type of carbon molecule that is produced by living things.

Detailed explanation-2: -Tribrachidium lived during a period of time called the Ediacaran, which ranged from 635 million to 541 million years ago. This period was characterised by a variety of large, complex organisms, most of which are difficult to link to any modern species.

Detailed explanation-3: -The first large multicellular organisms were the Ediacarans, ocean-dwelling life forms which appeared about 700 million years ago and disappeared around the time of the so-called Cambrian explosion 540 million years ago, when most of the familiar animal forms first evolved.

Detailed explanation-4: -Some variations increased their survival and allowed them to have more offspring. Over generations those advantageous variations would become more common-would, in a word, be “selected.” As new variations emerged and spread, they could gradually tinker with anatomy, producing complex structures.