Most* living cells have cell membranes (a.k.a. cell walls) - a containing layer which separates the cell's contents from the outside world.

The membranes were discovered shortly after the invention of the microscope in the 17th century, and their structure was the subject of intense debate for more than two centuries. It's now known that the membranes are formed from a lipid layer and membrane proteins.

How the very first membranes evolved - making 'cells' possible - is currently unknown.

Cell membranes are a key element of life because they keep the genetic material and metabolic machinery together. All present cell membranes are made of phospholipids, yet the nature of the first membranes and the origin of phospholipids are still under debate.

Source : PNAS, 2021 118 (22)

The paper cited above notes the discovery of a phospho-lipid precursor known as thanolamine (NH₂CH₂CH₂OH) in a molecular cloud in interstellar space. Raising the question of whether the first lipids suitable for building cell walls may have arrived on Earth from space.

* Note : Some bacteria don't have cell walls - see Cell wall deficient bacteriaplugin-autotooltip__plain plugin-autotooltip_bigCell Wall Deficient Bacteria and Disease

As the name suggests, Cell Wall Deficient Bacteria (CWDB) are a group of bacteria - originally identified in 1935 - which lack a normal cell wall, e.g. Bacillus subtilis.

Some research groups have suggested that CWDB might cause diseases in humans and other animals,

Also see :Life timespanplugin-autotooltip__plain plugin-autotooltip_bigLife on Earth (timespan)

There is currently no scientific agreement as to how long ago life on Earth evolved. Estimates, based on geological evidence, vary by about 200 million years - from between 3.85 billion years ago (Ga), and 3.65 Ga..

To date, the oldest undisputed fossils appear in rocks from 3.2 Ga, but recent carbon-dating techniques applied to rocks from and Primordial Soupplugin-autotooltip__plain plugin-autotooltip_bigPrimordial Soup

"In 1953 an iconic set of experiments showed that some of the chemical building blocks of life, such as amino acids, could form spontaneously in the atmospheric conditions thought to prevail on the primordial Earth. This gave rise to the idea that the early oceans were a "primordial soup" from which life somehow emerged.