# Biomass Refined: 99% of Organic Carbon in Soils
## 3 Results and Discussion
### Refinement of Soil Carbon Stocks (Terrain, Depth, Gomalin, Saprock)
#### 3.3.1 Soil Depth Considerations--Just Scratching the Surface  
It is becoming increasingly realized that soils are extraordinarily ancient and deep. Ref. [96] questioned _\"How Deep Is Soil?\"_ and, on page 601, noted: _\"The lower boundary of soil is difficult to determine precisely, so the Soil Survey Staff (1992) recommended that, **for convenience**, the lower limit of soil be considered to be at a **depth of 2 m\"_ [my bolding]. Yet most samples are still for only 20-30 cm or, at most, a metre or so.  
This is manifestly inadequate as [97] estimated 56% more SOC storage in the top 3 m of soil than in just the first metre, readily justifying doubling of superficial sample results. Ref. [98], in soils up to 5 m deep, found that layers below 90 cm accounted for approximately 80%, while the 0-30 cm layer represented only 10% of total SOC stored (i.e., \(\times 10\) for >30 cm). As noted in the Introduction, in Western Australia, ref. [21] had SOC values up to five times greater in soils at a depth > 1 m down to 35 m deep. Thus, mere depth doubling is also a modest outcome.  
Although often assumed or repeated that soils are only a metre or two deep, a summary by table 5 in ref. [54] has: _\"The mean absolute DTB_ [Depth to Bedrock, hereafter as DtB] _predicted was 33.6 m\"_ but a Mean and Maximum Absolute DtB shown was 13.1 m, and soil was up to 3.1 km deep in two USA samples, not for Peat nor Pernafrost--this for mineral soils (for details and email exchange with authors, please see--[[https://vermecology.wordpress.com/2024/02/20/dtb-2/](https://vermecology.wordpress.com/2024/02/20/dtb-2/)]([https://vermecology.wordpress.com/2024/02/20/dtb-2/](https://vermecology.wordpress.com/2024/02/20/dtb-2/)), accessed on 11 November 2024).  
For Peat, the deepest currently reported is perhaps in Phillipi, Greece, at 190 m and dating largely from the Pleistocene [99]. Pernafrost is known to extend as much as 1.6 km and also date to the Pleistocene (often referred to as the Ice Age) from 2.5 Ma or the Holocene from about 11,000 years ago. Mineral soils are allegedly much more ancient, some fossilized in rocks from over 4 billion years old [12], but mostly forming since 500 Ma ago. Thus, soils are proven to be both ancient and deep.  
Although [18] had a caveat that their \(\sim\)3300 Gt total SOC estimates could be as much as 700 Gt C smaller due to a revised depth to bedrock (DtB) by [56], this may be a wide underestimation. [PERSON] et al. do not give DtB estimates, but, for China alone, mean DtB was 42.20 m in a study by [100], whereas mean values predicted by [56] and figure 10b in ref. [54] were just 11.81 m and 26.64 m, respectively. This suggests the Pelletier model DtB is about half of [PERSON] et al.'s model, itself about half of the [PERSON] et al. model. Thus, rather than reduced, [PERSON] et al.'s figure may truly be doubled (or possibly quadrupled?), for greater depth, possibly to as much as \(>\)6600 Gt SOC!  
An effective depth of Peat vs. Permafrost peat is discussed further in the Peat section.  
Ref. [101] discovered depth is lacking from about half of the papers they surveyed. Moreover, the depth of the soil studied halved in the past 30 years. They said that, for a more complete understanding of soil processes, soil properties, and microbial communities, soils should be studied to a greater depth. This is attempted herein; hence, extrapolation from superficial results to account for full depth of soil profiles seems entirely appropriate and reasonable, albeit water tables influence deeper soils.  
Since soils are shown to be tens or thousands of metres deep, shallow samples are no longer tenable. Although quite justified, as with terrain, the mere doubling for soil or peat depth may be a most modest outcome, albeit this is routinely applied in the present work.